Annotation of wikisrc/tutorials/bus_space_tutorial.mdwn, revision 1.3

1.2       mspo        1: [[!toc ]]
1.1       mspo        2: 
1.3     ! mspo        3: ## Introduction
1.1       mspo        4: 
                      5: ### Why was this tutorial created?
                      6: 
                      7: -   Introductory-level documentation is scarce
                      8: 
                      9: -   Writing device drivers is often considered black magic
                     10: 
                     11: -   Reading the man pages won’t give you the big picture
                     12: 
                     13: -   BSD systems are always in need of new drivers
                     14: 
                     15: -   Device drivers are fun
                     16: 
                     17: ### What won’t be covered here?
                     18: 
                     19: We don’t have much time, so several ~~advanced~~ topics were omitted:
                     20: 
                     21: -   Interrupt handling
                     22: 
                     23: -   Direct Memory Access and the bus\_dma framework
                     24: 
                     25: -   Power management
                     26: 
                     27: -   Driver detachment
                     28: 
                     29: -   Drivers as kernel modules
                     30: 
                     31: -   Examples for buses other than PCI
                     32: 
                     33: -   Pretty much everything else...
                     34: 
                     35: However, once you finish this tutorial, you should be able to pursue
                     36: this knowledge yourself.
                     37: 
                     38: ### What is a driver anyway?
                     39: 
                     40: -   The interface between user space and hardware, implemented as a part
                     41:     of the kernel
                     42: 
                     43: -   The NetBSD drivers are written mostly in C
                     44: 
                     45: -   Sometimes they have machine dependent assembler parts, but this is a
                     46:     rare case
                     47: 
                     48: ### What do you need to write a driver?
                     49: 
                     50: -   C programming skills
                     51: 
                     52: -   Hardware documentation (or the ability to reverse engineer the
                     53:     hardware)
                     54: 
                     55: -   A reference driver implementation will help but is not essential
                     56: 
                     57: -   A NetBSD installation and kernel source, or a cross-build
                     58:     environment (the latter is usually preferred for development of
                     59:     drivers)
                     60: 
                     61: -   A lot of time, coffee and patience
                     62: 
                     63: ### Why is writing the device drivers considered difficult?
                     64: 
                     65: -   It’s not as difficult as you may expect, in fact during this
                     66:     tutorial we’ll prove that it’s quite easy
                     67: 
                     68: -   You need to think on a very low level
                     69: 
                     70:     -   Good understanding of computer architecture is a must
                     71: 
                     72: -   Often documentation is the main problem – writing the driver is not
                     73:     possible if you don’t understand how the device works
                     74: 
                     75:     -   No access to documentation (uncooperative hardware vendors,
                     76:         vendors out of business)
                     77: 
                     78:     -   Documentation is incomplete or plain wrong
                     79: 
                     80:     -   Reverse engineering can solve these problems but it’s a very
                     81:         time consuming process
                     82: 
                     83: The NetBSD driver model
                     84: =======================
                     85: 
                     86: ### The NetBSD kernel basics
                     87: 
                     88: -   NetBSD has a classic monolithic UNIX-like kernel - all drivers are
                     89:     running in the same address space
                     90: 
                     91: -   Thanks to the above, communication between drivers and other kernel
                     92:     layers is simple
                     93: 
                     94: -   However, it also means that one badly written driver can affect the
                     95:     whole kernel
                     96: 
                     97: -   Numerous in-kernel frameworks standardise the way drivers are
                     98:     written (bus\_space, autoconf, etc.)
                     99: 
                    100: ### The NetBSD source directory structure
                    101: 
                    102: -   We’ll only cover parts interesting for a device driver programmer
                    103: 
                    104: -   src/sys/
                    105: 
                    106:     - kernel source directory
                    107: 
                    108: -   src/sys/dev/
                    109: 
                    110:     - machine-independent device drivers
                    111: 
                    112: -   src/sys/arch/
                    113: 
                    114:     - port-specific or architecture-specific parts (such as the
                    115:     low-level system initialisation procedures or machine-dependent
                    116:     drivers)
                    117: 
                    118: -   src/sys/arch/\$PORTNAME/conf/
                    119: 
                    120:     - kernel configuration files for a given port
                    121: 
                    122: ### Kernel autoconfiguration framework - autoconf(9)
                    123: 
                    124: -   Autoconfiguration is the process of matching hardware devices with
                    125:     an appropriate device driver
                    126: 
                    127: -   The kernel message buffer (dmesg) contains information about
                    128:     autoconfiguration of devices
                    129: 
                    130: -   driver0 at bus0: Foo hardware
                    131: 
                    132:     -   Instance 0 of the driver has attached to instance 0 of the
                    133:         particular bus
                    134: 
                    135:     -   Such messages often carry additional bus-specific information
                    136:         about the exact location of the device (like the device and
                    137:         function number on the PCI bus)
                    138: 
                    139: -   driver0: some message
                    140: 
                    141:     -   Additional information about the driver state or device
                    142:         configuration
                    143: 
                    144: ### Autoconfiguration as seen in the dmesg
                    145: 
                    146:     NetBSD 6.99.12 (GENERIC) #7: Fri Oct  5 18:43:21 CEST 2012
                    147:             rkujawa@saiko.local:/Users/rkujawa/netbsd-eurobsdcon2012/src/sys/arch/cobalt/compile/obj/GENERIC
                    148:     Cobalt Qube 2
                    149:     total memory = 32768 KB
                    150:     avail memory = 27380 KB
                    151:     mainbus0 (root)
                    152:     com0 at mainbus0 addr 0x1c800000 level 3: ns16550a, working fifo
                    153:     com0: console
                    154:     cpu0 at mainbus0: QED RM5200 CPU (0x28a0) Rev. 10.0 with built-in FPU Rev. 1.0
                    155:     cpu0: 48 TLB entries, 256MB max page size
                    156:     cpu0: 32KB/32B 2-way set-associative L1 instruction cache
                    157:     cpu0: 32KB/32B 2-way set-associative write-back L1 data cache
                    158:     mcclock0 at mainbus0 addr 0x10000070: mc146818 compatible time-of-day clock
                    159:     panel0 at mainbus0 addr 0x1f000000
                    160:     gt0 at mainbus0 addr 0x14000000
                    161:     pci0 at gt0
                    162:     pchb0 at pci0 dev 0 function 0: Galileo GT-64011 System Controller, rev 1
                    163:     pcib0 at pci0 dev 9 function 0
                    164:     pcib0: VIA Technologies VT82C586 PCI-ISA Bridge, rev 57
                    165:     viaide0 at pci0 dev 9 function 1
                    166:     viaide0: VIA Technologies VT82C586 (Apollo VP) ATA33 controller
                    167:     viaide0: primary channel interrupting at irq 14
                    168:     atabus0 at viaide0 channel 0
                    169:     viaide0: secondary channel interrupting at irq 15
                    170:     atabus1 at viaide0 channel 1
                    171:     wd0 at atabus0 drive 0
                    172:     wd0: <netbsd-cobalt.img>
                    173:     wd0: 750 MB, 1524 cyl, 16 head, 63 sec, 512 bytes/sect x 1536192 sectors
                    174: 
                    175: ### Autoconfiguration as seen in the dmesg
                    176: 
                    177: ![image](img_cobaltdevices.png)
                    178: 
                    179: ### The bus\_space(9) framework
                    180: 
                    181: -   “The goal of the bus\_space functions is to allow a single driver
                    182:     source file to manipulate a set of devices on different system
                    183:     architectures, and to allow a single driver object file to
                    184:     manipulate a set of devices on multiple bus types on a single
                    185:     architecture.”
                    186: 
                    187: -   Provides a set of functions implementing common operations on the
                    188:     bus like mapping, reading, writing, copying, etc.
                    189: 
                    190: -   The bus\_space(9) is implemented at the machine-dependent level
                    191:     (typically it’s a part of architecture-specific code), but all
                    192:     implementations present the same interface[^1]
                    193: 
                    194: ### Machine independent drivers
                    195: 
                    196: -   If possible drivers should work on any hardware platform
                    197: 
                    198: -   High quality, machine-independent (MI) drivers are an important
                    199:     factor that adds to NetBSD portability
                    200: 
                    201: -   Some drivers are completely MI, some have MD or bus dependent
                    202:     attachments and some are completely MD
                    203: 
                    204:     -   A driver for a typical PCI card will be completely MI
                    205: 
                    206:     -   A driver for the components of a SoC will usually be completely
                    207:         MD
                    208: 
                    209: -   The bus\_space abstraction helps to achieve portability,
                    210:     transparently handling endianness issues and hiding bus
                    211:     implementation details from the device driver
                    212: 
                    213: -   Even if we have MI drivers, writing the drivers is always
                    214:     significant part of effort needed to port NetBSD to new hardware
                    215: 
                    216: Example driver from scratch
                    217: ===========================
                    218: 
                    219: ### Development environment
                    220: 
                    221: -   Out of scope of this course, but very well documented
                    222: 
                    223: -   Cross compiling is an easy task with the build.sh script
                    224: 
                    225: -   Described in [Part V of the NetBSD
                    226:     Guide](http://www.netbsd.org/docs/guide/en/part-compile.html)
                    227: 
                    228: -   Check out the NetBSD sources
                    229: 
                    230: -   \$ build.sh -m cobalt tools
                    231: 
                    232:     will build compiler, assembler, linker, etc. for cobalt port
                    233: 
                    234: -   \$ build.sh -m cobalt kernel=GENERIC
                    235: 
                    236:     will build the GENERIC kernel for cobalt
                    237: 
                    238: -   Call build.sh with a -u parameter to update (won’t rebuilding
                    239:     everything)
                    240: 
                    241: -   build.sh
                    242: 
                    243:     is calling nbconfig and nbmake tools, no magic involved
                    244: 
                    245: ### Quick introduction to GXemul
                    246: 
                    247: -   A framework for full-system computer architecture emulation,
                    248:     excellent for educational purposes
                    249: 
                    250: -   Capable of emulating several real machines supported by NetBSD
                    251: 
                    252: -   We’ll emulate a [Cobalt](http://en.wikipedia.org/wiki/Cobalt_Qube),
                    253:     MIPS-based micro server with PCI bus
                    254: 
                    255: -   I’ve modified GXemul and implemented an emulation of an additional
                    256:     PCI device
                    257: 
                    258: -   It will be used to show (almost) a real-life example of the driver
                    259:     development process
                    260: 
                    261: ### Our hardware - functional description
                    262: 
                    263: -   Business applications often use arithmetic operations like addition
                    264: 
                    265: -   Fake Cards Inc. responded to market needs and created a new product,
                    266:     Advanced Addition Accelerator
                    267: 
                    268: -   Pointy Haired Bosses will certainly buy it to accelerate their
                    269:     business applications, so let’s create a driver for NetBSD!
                    270: 
                    271: ### Our hardware - technical details
                    272: 
                    273: -   Overview
                    274: 
                    275:     -   Implemented as a PCI device
                    276: 
                    277:     -   Arithmetic unit capable of addition of two numbers
                    278: 
                    279:     -   Four[^2] registers in the PCI memory space
                    280: 
                    281: -   PCI configuration space
                    282: 
                    283:     -   Identified by the PCI vendor ID 0xfabc and product ID 0x0001
                    284: 
                    285:     -   Base Address Register 0x10 used to configure the engine address
                    286: 
                    287:     -   4 x 32-bit registers = 16 bytes
                    288: 
                    289:     -   Other configuration registers irrelevant
                    290: 
                    291: [faaop]
                    292: 
                    293: ### Our hardware - technical details (memory mapped register set)
                    294: 
                    295: -   Advanced Addition Acceleration registers
                    296: 
                    297:    Register Name   Offset                          Description
                    298:   --------------- -------- -----------------------------------------------------------
                    299:       COMMAND       0x4           Register used to issue commands to the engine
                    300:        DATA         0x8      Register used to load data to internal engine registers
                    301:       RESULT        0xC     Register used to store the result of arithmetic operation
                    302: 
                    303: -   COMMAND register
                    304: 
                    305:    Bit   R/W                                Description
                    306:   ----- ----- -----------------------------------------------------------------------
                    307:     0     W    Execute ADD operation on values loaded into internal register A and B
                    308:     1    R/W        Select internal register A for access through DATA register
                    309:     2    R/W        Select internal register B for access through DATA register
                    310: 
                    311: -   Selecting internal register A and B at the same time will lead to
                    312:     undefined behaviour
                    313: 
                    314: ### Our hardware - technical details (memory mapped register set)
                    315: 
                    316: -   DATA register
                    317: 
                    318:    Bit    R/W                     Description
                    319:   ------ ----- --------------------------------------------------
                    320:    0:31   R/W   Read/write the value in internal engine register
                    321: 
                    322: -   RESULT register
                    323: 
                    324:    Bit    R/W                Description
                    325:   ------ ----- ----------------------------------------
                    326:    0:31    R    Holds the result of last ADD operation
                    327: 
                    328: ### Our hardware - technical details (operation algorithm)
                    329: 
                    330: -   Select the internal register A for access (write 0x2 into COMMAND
                    331:     register)
                    332: 
                    333: -   Write the first number into DATA register
                    334: 
                    335: -   Select the internal register B for access (write 0x4 into COMMAND
                    336:     register)
                    337: 
                    338: -   Write the second number into DATA register
                    339: 
                    340: -   Issue the ADD operation (write 0x1 into COMMAND register)
                    341: 
                    342: -   Read the result from RESULT register
                    343: 
                    344: ### Adding a new driver to the NetBSD kernel
                    345: 
                    346: -   We’ll discuss the steps needed to add a new MI PCI device driver to
                    347:     the NetBSD kernel
                    348: 
                    349:     -   Add the vendor and device ID to the database of PCI IDs
                    350: 
                    351:     -   Create a set of the driver source files in
                    352:         src/sys/dev/\$BUSNAME/
                    353: 
                    354:     -   Add the new driver to src/sys/dev/\$BUSNAME/\$BUSNAME.files file
                    355: 
                    356:     -   Add the new driver to DEVNAMES[^3] file
                    357: 
                    358: ### Modifying the PCI device database
                    359: 
                    360:     unmatched vendor 0xfabc product 0x0001 (Co-processor 
                    361:     processor, revision 0x01) at pci0 dev 12 function 0 
                    362:     not configured
                    363: 
                    364: -   The kernel does not know anything about this vendor and device
                    365: 
                    366: -   Add it to the PCI device database - src/sys/dev/pci/pcidevs
                    367: 
                    368: -   vendor VENDORNAME 0xVENDORID Long Vendor Name
                    369: 
                    370: -   product VENDORNAME PRODUCTNAME 0xPRODUCTID Long Product Name
                    371: 
                    372: -   To regenerate pcidevs\*.h run awk -f devlist2h.awk pcidevs or
                    373:     Makefile.pcidevs if you’re on NetBSD
                    374: 
                    375: ### Modifying the PCI device database - example
                    376: 
                    377:     --- pcidevs 29 Sep 2012 10:26:14 -0000  1.1139
                    378:     +++ pcidevs 5 Oct 2012 08:52:59 -0000
                    379:     @@ -669,6 +669,7 @@
                    380:      vendor CHRYSALIS   0xcafe  Chrysalis-ITS
                    381:      vendor MIDDLE_DIGITAL  0xdeaf  Middle Digital
                    382:      vendor ARC     0xedd8  ARC Logic
                    383:     +vendor FAKECARDS   0xfabc  Fake Cards
                    384:      vendor INVALID     0xffff  INVALID VENDOR ID
                    385:      
                    386:      /*
                    387:     @@ -2120,6 +2121,9 @@
                    388:      /* Eumitcom products */
                    389:      product EUMITCOM WL11000P  0x1100  WL11000P PCI WaveLAN/IEEE 802.11
                    390:      
                    391:     +/* FakeCards products */
                    392:     +product FAKECARDS AAA      0x0001  Advanced Addition Accelerator
                    393:     +
                    394:      /* O2 Micro */
                    395:      product O2MICRO 00F7       0x00f7  Integrated OHCI IEEE 1394 Host Controller
                    396:      product O2MICRO OZ6729     0x6729  OZ6729 PCI-PCMCIA Bridge
                    397: 
                    398: ### Modifying the PCI device database - example
                    399: 
                    400:     Fake Cards Advanced Addition Accelerator (Co-processor 
                    401:     processor, revision 0x01) at pci0 dev 12 function 0 
                    402:     not configured
                    403: 
                    404: -   Now the kernel knows the vendor and product ID
                    405: 
                    406: -   But there’s still no driver for this device
                    407: 
                    408: ### Adding the new PCI driver
                    409: 
                    410: -   Choose a name - short, easy to remember, avoid numbers
                    411: 
                    412:     -   faa
                    413: 
                    414:         looks like a good name, but you can choose any name you like
                    415: 
                    416: -   Create a set of new files in src/sys/dev/pci
                    417: 
                    418:     -   faa.c
                    419: 
                    420:         - main driver code
                    421: 
                    422:     -   faareg.h
                    423: 
                    424:         - register definitions[^4]
                    425: 
                    426:     -   faavar.h
                    427: 
                    428:         - driver structures and functions used in other parts of the
                    429:         kernel[^5]
                    430: 
                    431: -   Modify driver definitions
                    432: 
                    433:     -   src/sys/dev/pci/files.pci
                    434: 
                    435:     -   src/sys/dev/DEVNAMES
                    436: 
                    437: -   Configure the kernel to use the newly added driver -
                    438:     src/sys/arch/\$PORTNAME/conf/GENERIC
                    439: 
                    440: ### Adding the new PCI driver - main driver
                    441: 
                    442: -   Kernel includes are at the beginning, followed by machine-specific
                    443:     and bus-specific includes
                    444: 
                    445: -   Should also include faareg.h and faavar.h files
                    446: 
                    447: -   A minimal driver needs just two functions
                    448: 
                    449:     -   faa\_match
                    450: 
                    451:         (or faa\_probe for some buses)
                    452: 
                    453:     -   faa\_attach
                    454: 
                    455: -   The CFATTACH\_DECL\_NEW macro plugs the above functions into
                    456:     autoconf(9) mechanism
                    457: 
                    458: ### Adding the new PCI driver - main driver
                    459: 
                    460: -   static int faa\_match(device\_t parent, cfdata\_t match, void
                    461:     \*aux);
                    462: 
                    463:     -   Check if the driver should attach to a given device (for example
                    464:         in case of PCI bus, it will be used to check vendor and product
                    465:         ID)
                    466: 
                    467:     -   parent
                    468: 
                    469:         - pointer to parent’s driver device structure
                    470: 
                    471:     -   match
                    472: 
                    473:         - pointer to autoconf(9) details structure
                    474: 
                    475:     -   aux
                    476: 
                    477:         - despite the name the most important argument, usually contains
                    478:         bus-specific structure describing device details
                    479: 
                    480: -   static void faa\_attach(device\_t parent, device\_t self, void
                    481:     \*aux);
                    482: 
                    483:     -   Attach the driver to a given device
                    484: 
                    485:     -   parent
                    486: 
                    487:         - same as with match function
                    488: 
                    489:     -   self
                    490: 
                    491:         - pointer to driver’s device structure
                    492: 
                    493:     -   aux
                    494: 
                    495:         - same as with match function
                    496: 
                    497: -   See definitions of these functions in the
                    498:     [driver(9)](http://netbsd.gw.com/cgi-bin/man-cgi?driver+9+NetBSD-current)
                    499:     man page.
                    500: 
                    501: ### Adding the new PCI driver - main driver cont’d
                    502: 
                    503: -   CFATTACH\_DECL\_NEW(faa, sizeof(struct faa\_softc), faa\_match,
                    504:     faa\_attach, NULL, NULL);
                    505: 
                    506:     -   driver name
                    507: 
                    508:     -   size of softc structure containing state of driver’s instance
                    509: 
                    510:     -   match/probe function
                    511: 
                    512:     -   attach function
                    513: 
                    514:     -   detach function
                    515: 
                    516:     -   activate function
                    517: 
                    518: -   The “\_NEW” name is unfortunate
                    519: 
                    520: -   Pass NULL for unimplemented functions
                    521: 
                    522: -   We won’t cover detach and activate now, as they are not needed for a
                    523:     simple driver
                    524: 
                    525: ### Adding the new PCI driver - main driver example
                    526: 
                    527: -   src/sys/dev/pci/faa.c
                    528: 
                    529: <!-- -->
                    530: 
                    531:     #include <sys/cdefs.h>
1.3     ! mspo      532:     __KERNEL_RCSID(0, "$NetBSD: bus_space_tutorial.mdwn,v 1.2 2013/06/23 14:10:19 mspo Exp $");
1.1       mspo      533:     #include <sys/param.h>
                    534:     #include <sys/device.h>
                    535:     #include <dev/pci/pcivar.h>
                    536:     #include <dev/pci/pcidevs.h>
                    537:     #include <dev/pci/faareg.h>
                    538:     #include <dev/pci/faavar.h>
                    539: 
                    540:     static int      faa_match(device_t, cfdata_t, void *);
                    541:     static void     faa_attach(device_t, device_t, void *);
                    542: 
                    543:     CFATTACH_DECL_NEW(faa, sizeof(struct faa_softc),
                    544:         faa_match, faa_attach, NULL, NULL);
                    545: 
                    546:     static int
                    547:     faa_match(device_t parent, cfdata_t match, void *aux)
                    548:     {
                    549:             return 0;
                    550:     }
                    551: 
                    552:     static void
                    553:     faa_attach(device_t parent, device_t self, void *aux)
                    554:     { 
                    555:     }
                    556: 
                    557: ### Adding the new PCI driver - auxiliary includes
                    558: 
                    559: -   src/sys/dev/pci/faareg.h
                    560: 
                    561: <!-- -->
                    562: 
                    563:     #ifndef FAAREG_H
                    564:     #define FAAREG_H
                    565:     /* 
                    566:      * Registers are defined using preprocessor:
                    567:      * #define FAA_REGNAME  0x0
                    568:      * We'll add them later, let's leave it empty for now.
                    569:      */
                    570:     #endif /* FAAREG_H */
                    571: 
                    572: -   src/sys/dev/pci/faavar.h
                    573: 
                    574: <!-- -->
                    575: 
                    576:     #ifndef FAAVAR_H
                    577:     #define FAAVAR_H
                    578: 
                    579:     /* sc_dev is an absolute minimum, we'll add more later */
                    580:     struct faa_softc {
                    581:             device_t sc_dev;
                    582:     };
                    583:     #endif /* FAAVAR_H */
                    584: 
                    585: ### Adding the new PCI driver - registering the driver (courtesy)
                    586: 
                    587: -   src/sys/dev/DEVNAMES
                    588: 
                    589: <!-- -->
                    590: 
                    591:     --- DEVNAMES    1 Sep 2012 11:19:58 -0000   1.279
                    592:     +++ DEVNAMES    6 Oct 2012 19:59:06 -0000
                    593:     @@ -436,6 +436,7 @@
                    594:      ex         MI
                    595:      exphy          MI
                    596:      ezload         MI      Attribute
                    597:     +faa            MI
                    598:      fb         luna68k
                    599:      fb         news68k
                    600:      fb         newsmips
                    601: 
                    602: ### Adding the new PCI driver - registering the driver
                    603: 
                    604: -   See config(5)
                    605: 
                    606: -   src/sys/dev/pci/files.pci
                    607: 
                    608: <!-- -->
                    609: 
                    610:     --- pci/files.pci   2 Aug 2012 00:17:44 -0000   1.360
                    611:     +++ pci/files.pci   6 Oct 2012 19:59:10 -0000
                    612:     @@ -1122,3 +1122,9 @@
                    613:      device tdvfb: wsemuldisplaydev, rasops8, vcons, videomode
                    614:      attach tdvfb at pci
                    615:      file   dev/pci/tdvfb.c     tdvfb   
                    616:     +
                    617:     +# FakeCards Advanced Addition Accelerator
                    618:     +device faa
                    619:     +attach faa at pci
                    620:     +file   dev/pci/faa.c       faa 
                    621:     +
                    622: 
                    623: ### Adding the new PCI driver to the kernel configuration
                    624: 
                    625: -   src/sys/arch/cobalt/conf/GENERIC
                    626: 
                    627: <!-- -->
                    628: 
                    629:     --- GENERIC 10 Mar 2012 21:51:50 -0000  1.134
                    630:     +++ GENERIC 6 Oct 2012 20:12:37 -0000
                    631:     @@ -302,6 +302,9 @@
                    632:      #fms*      at pci? dev ? function ?    # Forte Media FM801
                    633:      #sv*       at pci? dev ? function ?    # S3 SonicVibes
                    634:      
                    635:     +# Fake Cards Advanced Addition Accelerator
                    636:     +faa*       at pci? dev ? function ?
                    637:     +
                    638:      # Audio support
                    639:      #audio*        at audiobus?
                    640: 
                    641: -   The above definition means that an instance of faa may be attached
                    642:     to any PCI bus, any device, any function
                    643: 
                    644: -   The exact position of the rule in the configuration file is not
                    645:     important in this case
                    646: 
                    647: -   See
                    648:     [config(5)](http://netbsd.gw.com/cgi-bin/man-cgi?config+5+NetBSD-current)
                    649:     for a description of the device definition language
                    650: 
                    651: ### Adding the new PCI driver - example
                    652: 
                    653: -   The driver should compile now
                    654: 
                    655: -   The driver’s match function will check if the driver is able to work
                    656:     with a given device
                    657: 
                    658: -   Since it is not implemented, the kernel will not attach the driver
                    659: 
                    660: ### Matching the PCI device
                    661: 
                    662: -   Modify the faa\_match function to match the specified PCI device
                    663: 
                    664: -   Use PCI\_VENDOR and PCI\_PRODUCT macros to obtain the IDs
                    665: 
                    666: <!-- -->
                    667: 
                    668:     static int
                    669:     faa_match(device_t parent, cfdata_t match, void *aux)
                    670:     {
                    671:             const struct pci_attach_args *pa = (const struct pci_attach_args *)aux;
                    672: 
                    673:             if ((PCI_VENDOR(pa->pa_id) == PCI_VENDOR_FAKECARDS) 
                    674:                 && (PCI_PRODUCT(pa->pa_id) == PCI_PRODUCT_FAKECARDS_AAA))
                    675:                     return 1;
                    676: 
                    677:             return 0;
                    678:     }
                    679: 
                    680: ### Attaching to the PCI device
                    681: 
                    682:     faa0 at pci0 dev 12 function 0
                    683: 
                    684: -   The driver has successfully matched and attached to the PCI device
                    685:     but still is not doing anything useful
                    686: 
                    687: -   Let’s fill the attach function and actually program the hardware
                    688: 
                    689: ### Variable types used with bus\_space
                    690: 
                    691: -   bus\_space\_tag\_t
                    692: 
                    693:     – type used to describe a particular bus, usually passed to the
                    694:     driver from MI bus structures
                    695: 
                    696: -   bus\_space\_handle\_t
                    697: 
                    698:     – used to describe a mapped range of bus space, usually created with
                    699:     the bus\_space\_map() function
                    700: 
                    701: -   bus\_addr\_t
                    702: 
                    703:     – address on the bus
                    704: 
                    705: -   bus\_size\_t
                    706: 
                    707:     – an amount of space on the bus
                    708: 
                    709: -   Contents of these types are MD, so avoid modifying from within the
                    710:     driver[^6]
                    711: 
                    712: ### Why do we need to “map” the resources?
                    713: 
                    714: -   “The bus space must be mapped before it can be used, and should be
                    715:     unmapped when it is no longer needed”
                    716: 
                    717: -   It’s a machine-dependent process but it’s also conveniently hidden
                    718:     from the programmer by the bus\_space framework
                    719: 
                    720: ### Mapping the hardware resources
                    721: 
                    722: -   The generic bus\_space(9) way to map space
                    723: 
                    724: <!-- -->
                    725: 
                    726:     bus_space_map(bus_space_tag_t space, bus_addr_t address, 
                    727:     bus_size_t size, int flags, bus_space_handle_t  *handlep);
                    728: 
                    729: -   bus\_space\_map
                    730: 
                    731:     creates a mapping from the physical address to a kernel virtual
                    732:     address
                    733: 
                    734: -   space
                    735: 
                    736:     – represents the bus on which the mapping will be created
                    737: 
                    738: -   address
                    739: 
                    740:     – typically represents the physical address for which a mapping will
                    741:     be created
                    742: 
                    743: -   size
                    744: 
                    745:     – describes the amount of bus space to be mapped
                    746: 
                    747: -   handlep
                    748: 
                    749:     – pointer to mapped space (filled after successful mapping)
                    750: 
                    751: -   Separate space and address
                    752: 
                    753: ### Mapping the hardware resources
                    754: 
                    755: -   The PCI-specific way to map space
                    756: 
                    757: <!-- -->
                    758: 
                    759:     pci_mapreg_map(const struct pci_attach_args *pa, int reg, pcireg_t type, 
                    760:     int busflags, bus_space_tag_t *tagp, bus_space_handle_t *handlep, 
                    761:     bus_addr_t *basep, bus_size_t *sizep);
                    762: 
                    763: -   pci\_mapreg\_map
                    764: 
                    765:     creates mapping from physical address present in specified BAR
                    766:     register to kernel virtual address
                    767: 
                    768: -   pa
                    769: 
                    770:     – struct describing PCI attachment details (passed through aux)
                    771: 
                    772: -   reg
                    773: 
                    774:     – BAR register number
                    775: 
                    776: -   type
                    777: 
                    778:     – Select mapping type (I/O, memory)
                    779: 
                    780: -   busflags
                    781: 
                    782:     – Passed to bus\_space\_map flags argument
                    783: 
                    784: -   tagp
                    785: 
                    786:     – pointer to bus\_space\_tag
                    787: 
                    788: -   handlep
                    789: 
                    790:     – pointer to a mapped space
                    791: 
                    792: -   basep
                    793: 
                    794:     – address of a mapped space
                    795: 
                    796: -   sizep
                    797: 
                    798:     – size of mapped space (equivalent to BAR size)
                    799: 
                    800: -   The last four parameters are filled after successful mapping
                    801: 
                    802: ### Mapping the registers using BAR - adding auxiliary includes
                    803: 
                    804: -   src/sys/dev/pci/faareg.h
                    805: 
                    806: <!-- -->
                    807: 
                    808:     #define FAA_MMREG_BAR   0x10
                    809: 
                    810: -   src/sys/dev/pci/faavar.h
                    811: 
                    812: <!-- -->
                    813: 
                    814:     struct faa_softc {
                    815:             device_t sc_dev;
                    816: 
                    817:             bus_space_tag_t sc_regt;
                    818:             bus_space_handle_t sc_regh;
                    819:             bus_addr_t sc_reg_pa;
                    820: 
                    821:     };
                    822: 
                    823: ### Mapping the registers using BAR - main driver code
                    824: 
                    825: -   src/sys/dev/pci/faa.c
                    826: 
                    827: <!-- -->
                    828: 
                    829:     static void
                    830:     faa_attach(device_t parent, device_t self, void *aux)
                    831:     {
                    832:             struct faa_softc *sc = device_private(self);
                    833:             const struct pci_attach_args *pa = aux;
                    834: 
                    835:             sc->sc_dev = self;
                    836: 
                    837:             pci_aprint_devinfo(pa, NULL);
                    838: 
                    839:             if (pci_mapreg_map(pa, FAA_MMREG_BAR, PCI_MAPREG_TYPE_MEM, 0, 
                    840:                 &sc->sc_regt, &sc->sc_regh, &sc->sc_reg_pa, 0) != 0 ) {
                    841:                 aprint_error_dev(sc->sc_dev, "can't map the BAR\n");
                    842:                 return;
                    843:             }
                    844: 
                    845:             aprint_normal_dev(sc->sc_dev, "regs at 0x%08x\n", (uint32_t) sc->sc_reg_pa);
                    846:     }
                    847: 
                    848: ### Accessing the hardware registers
                    849: 
                    850: -   The bus\_space\_read\_ and bus\_space\_write\_ functions are basic
                    851:     methods of reading and writing the hardware registers
                    852: 
                    853: -   uintX\_t bus\_space\_read\_X(bus\_space\_tag\_t space,
                    854:     bus\_space\_handle\_t handle, bus\_size\_t offset);
                    855: 
                    856: -   void bus\_space\_write\_X(bus\_space\_tag\_t space,
                    857:     bus\_space\_handle\_t handle, bus\_size\_t offset, uintX\_t value);
                    858: 
                    859:     -   space
                    860: 
                    861:         - tag describing the bus
                    862: 
                    863:     -   handle
                    864: 
                    865:         - describes the exact location on the bus where read/write
                    866:         should occur, this handle is obtained by bus\_space\_map
                    867: 
                    868:     -   offset
                    869: 
                    870:         - offset from handle location
                    871: 
                    872:     -   The read function returns the data read from the specified
                    873:         location, while write has an argument value which should be
                    874:         filled with data to be written
                    875: 
                    876: ### Variants of bus\_space\_read and bus\_space\_write
                    877: 
                    878:     Data       Read function         Write function
                    879:   -------- --------------------- ----------------------
                    880:    8-bit    bus\_space\_read\_1   bus\_space\_write\_1
                    881:    16-bit   bus\_space\_read\_2   bus\_space\_write\_2
                    882:    32-bit   bus\_space\_read\_4   bus\_space\_write\_4
                    883:    64-bit   bus\_space\_read\_8   bus\_space\_write\_8
                    884: 
                    885: -   There are many more variants of read and write functions and they
                    886:     are useful in certain situations, see the
                    887:     [bus\_space(9)](http://netbsd.gw.com/cgi-bin/man-cgi?bus_space++NetBSD-current)
                    888:     man page
                    889: 
                    890: ### Accessing the hardware registers - example
                    891: 
                    892: -   Create a function that will write a value into the DATA register of
                    893:     our device, then read it back and check if the value is the same as
                    894:     written
                    895: 
                    896: -   Define the DATA register in the driver
                    897: 
                    898: -   src/sys/dev/pci/faareg.h
                    899: 
                    900: <!-- -->
                    901: 
                    902:     #define FAA_DATA                0x8
                    903:     #define FAA_COMMAND             0x4
                    904:     #define FAA_COMMAND_STORE_A         __BIT(1)
                    905: 
                    906: -   Define the new function in main driver code
                    907: 
                    908: -   static bool faa\_check(struct faa\_softc \*sc);
                    909: 
                    910: ### Accessing the hardware registers - example
                    911: 
                    912: -   src/sys/dev/pci/faa.c
                    913: 
                    914: <!-- -->
                    915: 
                    916:     static void
                    917:     faa_attach(device_t parent, device_t self, void *aux)
                    918:     {
                    919:        /* ... */
                    920:        if (!faa_check(sc)) {
                    921:             aprint_error_dev(sc->sc_dev, "hardware not responding\n");
                    922:             return;
                    923:        }
                    924:     }
                    925: 
                    926:     static bool
                    927:     faa_check(struct faa_softc *sc)
                    928:     {
                    929:             uint32_t testval = 0xff11ee22; 
                    930:             bus_space_write_4(sc->sc_regt, sc->sc_regh, FAA_COMMAND, FAA_COMMAND_STORE_A);
                    931:             bus_space_write_4(sc->sc_regt, sc->sc_regh, FAA_DATA, testval);
                    932:             if (bus_space_read_4(sc->sc_regt, sc->sc_regh, FAA_DATA) == testval)
                    933:                     return true;
                    934: 
                    935:             return false;
                    936:     }
                    937: 
                    938: ### Accessing the hardware registers - running the example
                    939: 
                    940: -   Update the kernel binary and run it again
                    941: 
                    942: -   Check the GXemul log
                    943: 
                    944: <!-- -->
                    945: 
                    946:     [ faa: COMMAND register (0x4) WRITE value 0x2 ]
                    947:     [ faa: DATA register (0x8) WRITE value 0xff11ee22 ]
                    948:     [ faa: DATA register (0x8) READ value 0xff11ee22 ]
                    949: 
                    950: -   GXemul will conveniently display all accesses to our device
                    951: 
                    952: -   The faa driver still does attach without error, which means that the
                    953:     check function is working properly
                    954: 
                    955: <!-- -->
                    956: 
                    957:     faa0 at pci0 dev 12 function 0: Fake Cards Advanced Addition Accelerator (rev. 0x01)
                    958:     faa0: registers at 0x10110000
                    959: 
                    960: ### Implementing addition using the hardware
                    961: 
                    962: -   The basic principle of device operation should be laid out in the
                    963:     data sheet
                    964: 
                    965: -   We need to implement an algorithm based on this description
                    966: 
                    967: -   Writing such an algorithm is often not needed, since the NetBSD
                    968:     kernel already has frameworks for common device types (such as
                    969:     atabus/wd for IDE and SATA hard disk controllers, wsdisplay/wscons
                    970:     for frame buffers, etc.)
                    971: 
                    972: ### Implementing addition using the hardware
                    973: 
                    974: -   Define all registers
                    975: 
                    976: -   src/sys/dev/pci/faareg.h
                    977: 
                    978: <!-- -->
                    979: 
                    980:     #define FAA_STATUS              0x0
                    981:     #define FAA_COMMAND             0x4
                    982:     #define FAA_COMMAND_ADD             __BIT(0)        
                    983:     #define FAA_COMMAND_STORE_A         __BIT(1)
                    984:     #define FAA_COMMAND_STORE_B         __BIT(2)
                    985:     #define FAA_DATA                0x8
                    986:     #define FAA_RESULT              0xC
                    987: 
                    988: ### Implementing addition using the hardware
                    989: 
                    990: -   Add a new function to the main driver code
                    991: 
                    992: -   src/sys/dev/pci/faa.c
                    993: 
                    994: <!-- -->
                    995: 
                    996:     static void
                    997:     faa_attach(device_t parent, device_t self, void *aux)
                    998:     {
                    999:             /* ... */
                   1000:             aprint_normal_dev(sc->sc_dev, "just checking: 1 + 2 = %d\n", faa_add(sc, 1, 2));
                   1001:     }
                   1002: 
                   1003:     static uint32_t
                   1004:     faa_add(struct faa_softc *sc, uint32_t a, uint32_t b)
                   1005:     {
                   1006:             bus_space_write_4(sc->sc_regt, sc->sc_regh, FAA_COMMAND, FAA_COMMAND_STORE_A);
                   1007:             bus_space_write_4(sc->sc_regt, sc->sc_regh, FAA_DATA, a);
                   1008:             bus_space_write_4(sc->sc_regt, sc->sc_regh, FAA_COMMAND, FAA_COMMAND_STORE_B);
                   1009:             bus_space_write_4(sc->sc_regt, sc->sc_regh, FAA_DATA, b);
                   1010:             bus_space_write_4(sc->sc_regt, sc->sc_regh, FAA_COMMAND, FAA_COMMAND_ADD);
                   1011:             return bus_space_read_4(sc->sc_regt, sc->sc_regh, FAA_RESULT);
                   1012:     }
                   1013: 
                   1014: ### Implementing addition using the hardware - running the example
                   1015: 
                   1016: -   Update the kernel binary and run it again
                   1017: 
                   1018: -   Check GXemul log
                   1019: 
                   1020: <!-- -->
                   1021: 
                   1022:     [ faa: COMMAND register (0x4) WRITE value 0x2 ]
                   1023:     [ faa: DATA register (0x8) WRITE value 0x1 ]
                   1024:     [ faa: COMMAND register (0x4) WRITE value 0x4 ]
                   1025:     [ faa: DATA register (0x8) WRITE value 0x2 ]
                   1026:     [ faa: COMMAND register (0x4) WRITE value 0x1 ]
                   1027:     [ faa: RESULT register (0xC) READ value 0x3 ]
                   1028: 
                   1029: -   Looks like it worked!
                   1030: 
                   1031: <!-- -->
                   1032: 
                   1033:     faa0 at pci0 dev 12 function 0: Fake Cards Advanced Addition Accelerator (rev. 0x01)
                   1034:     faa0: registers at 0x10110000
                   1035:     faa0: just checking: 1 + 2 = 3
                   1036: 
1.3     ! mspo     1037: ## Interacting with userspace
1.1       mspo     1038: 
                   1039: ### The kernel-user space interface
                   1040: 
                   1041: -   Now that the core functionality of the kernel driver is working, it
                   1042:     should be exposed to user space
                   1043: 
                   1044: -   The interface between kernel driver and userspace can be designed in
                   1045:     many different ways
                   1046: 
                   1047: -   The classic UNIX way of interfacing between the kernel and user
                   1048:     space is a device file
                   1049: 
                   1050: -   Even when using device files there is no single interfacing method
                   1051:     that fits all use cases
                   1052: 
                   1053: -   It’s up to the programmer to define the communication protocol
                   1054: 
                   1055: ### Device files
                   1056: 
                   1057: -   crw-r—– 1 root wheel 101, 1 Aug 12 21:53 /dev/file
                   1058: 
                   1059: -   The kernel identifies which driver should service the request to
                   1060:     this file by using major and minor numbers (101 and 1 in the example
                   1061:     above)
                   1062: 
                   1063: -   The major number identifies the driver
                   1064: 
                   1065: -   The minor number usually identifies the driver instance, although
                   1066:     the driver is free to use it in any other way
                   1067: 
                   1068: -   In NetBSD device files are created statically
                   1069: 
                   1070:     -   By the MAKEDEV script during installation or boot
                   1071: 
                   1072:     -   Manually by using the mknod utility
                   1073: 
                   1074: ### Operations on device files
                   1075: 
                   1076: -   [open(2)](http://netbsd.gw.com/cgi-bin/man-cgi?read++NetBSD-current)
                   1077:     and
                   1078:     [close(2)](http://netbsd.gw.com/cgi-bin/man-cgi?read++NetBSD-current)
                   1079: 
                   1080: -   [read(2)](http://netbsd.gw.com/cgi-bin/man-cgi?read++NetBSD-current)
                   1081:     and
                   1082:     [write(2)](http://netbsd.gw.com/cgi-bin/man-cgi?write++NetBSD-current)
                   1083: 
                   1084: -   [ioctl(2)](http://netbsd.gw.com/cgi-bin/man-cgi?write++NetBSD-current)
                   1085: 
                   1086: -   [poll(2)](http://netbsd.gw.com/cgi-bin/man-cgi?poll++NetBSD-current)
                   1087: 
                   1088: -   [mmap(2)](http://netbsd.gw.com/cgi-bin/man-cgi?write++NetBSD-current)
                   1089: 
                   1090: -   and more…
                   1091: 
                   1092: -   Any mix of the above system calls might be used to interface between
                   1093:     the kernel and user space
                   1094: 
                   1095: -   We’ll implement an ioctl(2)-based communication mechanism
                   1096: 
                   1097: ### Adding cdevsw
                   1098: 
                   1099: -   cdevsw
                   1100: 
                   1101:     is used to decide which operation on the character device file calls
                   1102:     which driver function
                   1103: 
                   1104: -   Not all calls have to be implemented, although some device layers
                   1105:     define a set of calls that a driver must implement
                   1106: 
                   1107: -   For example disk drivers must implement open, close, read, write and
                   1108:     ioctl
                   1109: 
                   1110: -   src/sys/dev/pci/faa.c
                   1111: 
                   1112: <!-- -->
                   1113: 
                   1114:     dev_type_open(faaopen);
                   1115:     dev_type_close(faaclose);
                   1116:     dev_type_ioctl(faaioctl);
                   1117: 
                   1118:     const struct cdevsw faa_cdevsw = {
                   1119:             faaopen, faaclose, noread, nowrite, faaioctl,
                   1120:             nostop, notty, nopoll, nommap, nokqfilter, D_OTHER
                   1121:     };
                   1122: 
                   1123: ### Prototyping the cdevsw operations
                   1124: 
                   1125: -   The dev\_type\* macros are used to prototype the functions passed to
                   1126:     cdevsw
                   1127: 
                   1128: -   Pass no followed by a function name to the appropriate cdevsw field
                   1129:     if it is not implemented
                   1130: 
                   1131: -   There’s also bdevsw for block devices, but we won’t use it in this
                   1132:     example
                   1133: 
                   1134: -   The last member of the cdevsw structure defines the device flags,
                   1135:     originally it was used to define the device type (still used for
                   1136:     disks, tape drives and ttys, for other devices pass D\_OTHER)
                   1137: 
                   1138: ### Implemeting the cdevsw operations - open / close
                   1139: 
                   1140: -   src/sys/dev/pci/faa.c
                   1141: 
                   1142: <!-- -->
                   1143: 
                   1144:     int
                   1145:     faaopen(dev_t dev, int flags, int mode, struct lwp *l)
                   1146:     {
                   1147:             struct faa_softc *sc;
                   1148:             sc = device_lookup_private(&faa_cd, minor(dev));
                   1149: 
                   1150:             if (sc == NULL)
                   1151:                     return ENXIO;
                   1152:             if (sc->sc_flags & FAA_OPEN)
                   1153:                     return EBUSY;
                   1154: 
                   1155:             sc->sc_flags |= FAA_OPEN;
                   1156:             return 0;
                   1157:     }
                   1158:     int
                   1159:     faaclose(dev_t dev, int flag, int mode, struct lwp *l)
                   1160:     {
                   1161:             struct faa_softc *sc;
                   1162:             sc = device_lookup_private(&faa_cd, minor(dev));
                   1163: 
                   1164:             if (sc->sc_flags & FAA_OPEN)
                   1165:                     sc->sc_flags =~ FAA_OPEN;
                   1166: 
                   1167:             return 0;
                   1168:     }
                   1169: 
                   1170: ### Defining the ioctls
                   1171: 
                   1172: -   ioctl(2)
                   1173: 
                   1174:     can be used to call kernel-level functions and exchange data between
                   1175:     the kernel and user space
                   1176: 
                   1177: -   The classic way of passing data is by using structures, their
                   1178:     definitions are shared between the kernel and user space code
                   1179: 
                   1180: -   The driver might support more than one ioctl, the \_IO\* macros are
                   1181:     used to define the operation and associated structure used to
                   1182:     exchange data
                   1183: 
                   1184:     -   \_IO
                   1185: 
                   1186:         - just a kernel function call, no data exchange
                   1187: 
                   1188:     -   \_IOR
                   1189: 
                   1190:         - kernel function call and data pass from kernel to user space
                   1191: 
                   1192:     -   \_IOW
                   1193: 
                   1194:         - kernel function call and data pass from user space to kernel
                   1195: 
                   1196:     -   \_IOWR
                   1197: 
                   1198:         - kernel function call and data exchange in both directions
                   1199: 
                   1200:     -   \#define DRIVERIO\_IOCTLNAME \_IOXXX(group, ioctl\_number, data
                   1201:         structure)
                   1202: 
1.3     ! mspo     1203: ## Using ioctls
1.1       mspo     1204: 
                   1205: ### Defining the ioctls
                   1206: 
                   1207: -   src/sys/dev/pci/faaio.h
                   1208: 
                   1209: <!-- -->
                   1210: 
                   1211:     #include <sys/ioccom.h>
                   1212:                          
                   1213:     #define FAAIO_ADD   _IOWR(0, 1, struct faaio_add)
                   1214: 
                   1215:     struct faaio_add {
                   1216:         uint32_t a;
                   1217:         uint32_t b;
                   1218:         uint32_t *result;
                   1219:     };
                   1220: 
                   1221: -   In the above example the ioctl group is not defined (0), but a
                   1222:     single letter identifier could appear as first argument to \_IOWR
                   1223: 
                   1224: ### Implemeting the cdevsw operations - ioctl
                   1225: 
                   1226: -   src/sys/dev/pci/faa.c
                   1227: 
                   1228: <!-- -->
                   1229: 
                   1230:     int
                   1231:     faaioctl(dev_t dev, u_long cmd, void *data, int flag, struct lwp *l)
                   1232:     {
                   1233:             struct faa_softc *sc = device_lookup_private(&faa_cd, minor(dev));
                   1234:             int err;
                   1235: 
                   1236:             switch (cmd) {
                   1237:             case FAAIO_ADD:
                   1238:                     err = faaioctl_add(sc, (struct faaio_add *) data);
                   1239:                     break;
                   1240:             default:
                   1241:                     err = EINVAL;
                   1242:                     break;
                   1243:             }
                   1244:             return(err);
                   1245:     }
                   1246:     static int
                   1247:     faaioctl_add(struct faa_softc *sc, struct faaio_add *data)
                   1248:     {
                   1249:             uint32_t result; int err;
                   1250: 
                   1251:             aprint_normal_dev(sc->sc_dev, "got ioctl with a %d, b %d\n",
                   1252:                 data->a, data->b);
                   1253: 
                   1254:             result = faa_add(sc, data->a, data->b);
                   1255:             err = copyout(&result, data->result, sizeof(uint32_t));
                   1256:             return err;
                   1257:     }
                   1258: 
                   1259: ### Using copyout to pass data to userspace
                   1260: 
                   1261: -   The copy(9) functions are used to copy kernel space data from/to
                   1262:     user space
                   1263: 
                   1264: -   copyout(kernel\_address, user space\_address, size);
                   1265: 
                   1266: -   Actually on Cobalt we could just do data-\>result = faa\_add();
                   1267:     instead of calling the copyout function, but that is a bad idea
                   1268: 
                   1269: -   Some architectures (such as sparc64) have totally separate kernel
                   1270:     and user address spaces $ \implies $ user space addresses are
                   1271:     meaningless in the kernel
                   1272: 
                   1273: ### Defining device major number
                   1274: 
                   1275: -   Device major numbers for hardware drivers are usually defined in a
                   1276:     per-port manner[^7]
                   1277: 
                   1278: -   src/sys/arch/\$PORTNAME/conf/majors.\$PORTNAME
                   1279: 
                   1280: -   src/sys/arch/cobalt/conf/majors.cobalt
                   1281: 
                   1282: -   The following defines a new character device file called /dev/faa\*
                   1283:     with major number 101, but only if the faa driver is included in the
                   1284:     kernel (last argument)
                   1285: 
                   1286: -   device-major faa char 101 faa
                   1287: 
                   1288: ### Creating the device node
                   1289: 
                   1290: -   The mknod utility can be used to create the device file manually
                   1291: 
                   1292: -   The driver name can be specified instead of the major number - it
                   1293:     will be automatically resolved into the correct major number
                   1294: 
                   1295: -   mknod name [b | c] [major | driver] minor
                   1296: 
                   1297: -   mknod /dev/faa0 c faa 0
                   1298: 
                   1299: -   Created successfully
                   1300: 
                   1301: -   crw-r–r– 1 root wheel 101, 0 Oct 8 2012 /dev/faa0
                   1302: 
                   1303: ### An example user space program
                   1304: 
                   1305: -   The example program will open the device file and call ioctl(2) on
                   1306:     it
                   1307: 
                   1308: -   As simple as possible, just to show how communication is done
                   1309: 
                   1310: -   Using ioctls from the user space
                   1311: 
                   1312:     -   Open the device file with O\_RDWR
                   1313: 
                   1314:     -   Call ioctl(2) with the operation number and structure as
                   1315:         parameters
                   1316: 
                   1317: ### An example user space program - source
                   1318: 
                   1319:     void add(int, uint32_t, uint32_t);
                   1320: 
                   1321:     static const char* faa_device = "/dev/faa0";
                   1322: 
                   1323:     int
                   1324:     main(int argc, char *argv[])
                   1325:     {
                   1326:             int devfd;
                   1327: 
                   1328:             if (argc != 3) {
                   1329:                     printf("usage: %s a b\n", argv[0]);
                   1330:                     return 1;
                   1331:             }
                   1332:             if ( (devfd = open(faa_device, O_RDWR)) == -1) {
                   1333:                     perror("can't open device file");
                   1334:                     return 1;
                   1335:             }
                   1336: 
                   1337:             add(devfd, atoi(argv[1]), atoi(argv[2]));
                   1338: 
                   1339:             close(devfd);
                   1340:             return 0;
                   1341:     }
                   1342: 
                   1343: ### An example user space program - source
                   1344: 
                   1345:     void
                   1346:     add(int devfd, uint32_t a, uint32_t b)
                   1347:     {
                   1348:             struct faaio_add faaio;
                   1349:             uint32_t result = 0;
                   1350: 
                   1351:             faaio.result = &result;
                   1352:             faaio.a = a;
                   1353:             faaio.b = b;
                   1354: 
                   1355:             if (ioctl(devfd, FAAIO_ADD, &faaio) == -1) {
                   1356:                     perror("ioctl failed");
                   1357:             }
                   1358:             printf("%d\n", result);
                   1359:     }
                   1360: 
                   1361: ### An example user space program - running it
                   1362: 
                   1363:     # make
                   1364:     cc -o aaa_add aaa_add.c
                   1365:     # ./aaa_add 3 7
                   1366:     faa0: got ioctl with a 3, b 7
                   1367:     10
                   1368: 
                   1369: -   The program is successfully accessing the faa driver through the
                   1370:     ioctl
                   1371: 
                   1372: -   The faa0:... line is a kernel message, normally only seen on the
                   1373:     console terminal
                   1374: 
1.3     ! mspo     1375: ## A few tips
1.1       mspo     1376: 
                   1377: ### Avoiding common pitfalls
                   1378: 
                   1379: -   Always free resources allocated in the match or probe functions
                   1380: 
                   1381: -   Always use bus\_space methods, don’t access the hardware using a
                   1382:     pointer dereference
                   1383: 
                   1384: -   If possible test on more than one hardware architecture, some bugs
                   1385:     may surface
                   1386: 
                   1387: -   Don’t reinvent the wheel, try to use existing kernel frameworks as
                   1388:     much as possible
                   1389: 
                   1390: -   Use copy(9) (or uiomove(9) or store(9)/fetch(9)) to move data
                   1391:     between the kernel and user space
                   1392: 
                   1393: ### Basic driver debugging
                   1394: 
                   1395: -   Use aprint\_debug to print debug-level messages on console and log
                   1396:     them (enabled by passing AB\_DEBUG from the boot loader)
                   1397: 
                   1398: -   Use the built-in DDB debugger
                   1399: 
                   1400:     -   Enabled by the kernel option DDB
                   1401: 
                   1402:     -   A kernel panic will start DDB if the DDB\_ONPANIC=1 kernel
                   1403:         option is specified or the ddb.onpanic sysctl is set to 1.
                   1404: 
                   1405:     -   Run \# sysctl -w kern.panic\_now=1 to trigger a panic manually
                   1406:         (DIAGNOSTIC option)
                   1407: 
                   1408: -   Remote debugging is possible on some ports
                   1409: 
                   1410:     -   With KGDB through the serial port
                   1411: 
                   1412:     -   With IPKDB through the network
                   1413: 
1.3     ! mspo     1414: ## Summary
1.1       mspo     1415: 
                   1416: ### Further reading
                   1417: 
                   1418: -   Documentation, articles:
                   1419: 
                   1420:     -   [A Machine-Independent DMA Framework for NetBSD, Jason R.
                   1421:         Thorpe](http://www.netbsd.org/docs/kernel/bus_dma.pdf)
                   1422: 
                   1423:     -   [Writing Drivers for NetBSD, Jochen
                   1424:         Kunz](ftp://ftp.netbsd.org/pub/NetBSD/misc/ddwg/NetBSD-driver_writing-1.0.1e.pdf)
                   1425: 
                   1426:     -   [NetBSD Documentation: Writing a pseudo
                   1427:         device](http://www.netbsd.org/docs/kernel/pseudo/)
                   1428: 
                   1429:     -   [autoconf(9)](http://netbsd.gw.com/cgi-bin/man-cgi?autoconf+9+NetBSD-current),
                   1430:         [bus\_space(9)](http://netbsd.gw.com/cgi-bin/man-cgi?bus_space+9+NetBSD-current)
                   1431:         [bus\_dma(9)](http://netbsd.gw.com/cgi-bin/man-cgi?bus_dma+9+NetBSD-current)
                   1432:         [driver(9)](http://netbsd.gw.com/cgi-bin/man-cgi?driver+9+NetBSD-current),
                   1433:         [pci(9)](http://netbsd.gw.com/cgi-bin/man-cgi?pci+9+NetBSD-current)
                   1434:         man pages, etc.
                   1435: 
                   1436: -   Example source code of drivers:
                   1437: 
                   1438:     -   tdvfb
                   1439: 
                   1440:         , voodoofb are fairly good frame buffer driver examples with
                   1441:         documentation publicly available.
                   1442: 
                   1443:     -   etsec
                   1444: 
                   1445:         is a nice example of a more complicated network interface driver
                   1446: 
                   1447: ### Get the source code
                   1448: 
                   1449: -   Download the source code and materials for this tutorial
                   1450: 
                   1451: -   <https://github.com/rkujawa/busspace-tutorial>
                   1452: 
                   1453: -   <https://github.com/rkujawa/gxemul-tutorial>
                   1454: 
                   1455: ### Questions?
                   1456: 
                   1457: -   Do you have any questions?
                   1458: 
                   1459: ### The End…
                   1460: 
                   1461: ![image](NetBSD.png)
                   1462: 
                   1463: Thank you!
                   1464: 
                   1465: [^1]: At least they should, some functions are missing on less popular
                   1466:     ports
                   1467: 
                   1468: [^2]: Only three of these registers are of any importance for us at this
                   1469:     moment
                   1470: 
                   1471: [^3]: Required if you are NetBSD developer, optional otherwise.
                   1472: 
                   1473: [^4]: Might not exist if the driver is only a simple passthrough from a
                   1474:     specific bus to another MI driver.
                   1475: 
                   1476: [^5]: Omitted if not needed.
                   1477: 
                   1478: [^6]: although you’ll often have to use bus\_size\_t
                   1479: 
                   1480: [^7]: It’s also possible to define a major in a machine-independent way
                   1481:     in src/sys/conf/majors

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