Annotation of wikisrc/tutorials/bus_space_tutorial.mdwn, revision 1.11

1.9       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: -   Writing device drivers is often considered black magic
                      9: -   Reading the man pages won’t give you the big picture
                     10: -   BSD systems are always in need of new drivers
                     11: -   Device drivers are fun
                     12: 
                     13: ### What won’t be covered here?
                     14: 
                     15: We don’t have much time, so several ~~advanced~~ topics were omitted:
                     16: 
                     17: -   Interrupt handling
                     18: -   Direct Memory Access and the bus\_dma framework
                     19: -   Power management
                     20: -   Driver detachment
                     21: -   Drivers as kernel modules
                     22: -   Examples for buses other than PCI
                     23: -   Pretty much everything else...
                     24: 
                     25: However, once you finish this tutorial, you should be able to pursue
                     26: this knowledge yourself.
                     27: 
                     28: ### What is a driver anyway?
                     29: 
                     30: -   The interface between user space and hardware, implemented as a part
                     31:     of the kernel
                     32: -   The NetBSD drivers are written mostly in C
                     33: -   Sometimes they have machine dependent assembler parts, but this is a
                     34:     rare case
                     35: 
                     36: ### What do you need to write a driver?
                     37: 
                     38: -   C programming skills
                     39: -   Hardware documentation (or the ability to reverse engineer the
                     40:     hardware)
                     41: -   A reference driver implementation will help but is not essential
                     42: -   A NetBSD installation and kernel source, or a cross-build
                     43:     environment (the latter is usually preferred for development of
                     44:     drivers)
                     45: -   A lot of time, coffee and patience
                     46: 
                     47: ### Why is writing the device drivers considered difficult?
                     48: 
                     49: -   It’s not as difficult as you may expect, in fact during this
                     50:     tutorial we’ll prove that it’s quite easy
                     51: -   You need to think on a very low level
                     52:     -   Good understanding of computer architecture is a must
                     53: -   Often documentation is the main problem – writing the driver is not
                     54:     possible if you don’t understand how the device works
                     55:     -   No access to documentation (uncooperative hardware vendors,
                     56:         vendors out of business)
                     57:     -   Documentation is incomplete or plain wrong
                     58:     -   Reverse engineering can solve these problems but it’s a very
                     59:         time consuming process
                     60: 
1.4       mspo       61: ## The NetBSD driver model
1.1       mspo       62: 
                     63: ### The NetBSD kernel basics
                     64: 
                     65: -   NetBSD has a classic monolithic UNIX-like kernel - all drivers are
                     66:     running in the same address space
                     67: -   Thanks to the above, communication between drivers and other kernel
                     68:     layers is simple
                     69: -   However, it also means that one badly written driver can affect the
                     70:     whole kernel
                     71: -   Numerous in-kernel frameworks standardise the way drivers are
                     72:     written (bus\_space, autoconf, etc.)
                     73: 
                     74: ### The NetBSD source directory structure
                     75: 
                     76: -   We’ll only cover parts interesting for a device driver programmer
                     77: -   src/sys/
                     78:     - kernel source directory
                     79: -   src/sys/dev/
                     80:     - machine-independent device drivers
                     81: -   src/sys/arch/
                     82:     - port-specific or architecture-specific parts (such as the
                     83:     low-level system initialisation procedures or machine-dependent
                     84:     drivers)
1.6       mspo       85: -   src/sys/arch/$PORTNAME/conf/
1.1       mspo       86:     - kernel configuration files for a given port
                     87: 
                     88: ### Kernel autoconfiguration framework - autoconf(9)
                     89: 
                     90: -   Autoconfiguration is the process of matching hardware devices with
                     91:     an appropriate device driver
                     92: -   The kernel message buffer (dmesg) contains information about
                     93:     autoconfiguration of devices
                     94: -   driver0 at bus0: Foo hardware
                     95:     -   Instance 0 of the driver has attached to instance 0 of the
                     96:         particular bus
                     97:     -   Such messages often carry additional bus-specific information
                     98:         about the exact location of the device (like the device and
                     99:         function number on the PCI bus)
                    100: -   driver0: some message
                    101:     -   Additional information about the driver state or device
                    102:         configuration
                    103: 
                    104: ### Autoconfiguration as seen in the dmesg
                    105: 
                    106:     NetBSD 6.99.12 (GENERIC) #7: Fri Oct  5 18:43:21 CEST 2012
                    107:             rkujawa@saiko.local:/Users/rkujawa/netbsd-eurobsdcon2012/src/sys/arch/cobalt/compile/obj/GENERIC
                    108:     Cobalt Qube 2
                    109:     total memory = 32768 KB
                    110:     avail memory = 27380 KB
                    111:     mainbus0 (root)
                    112:     com0 at mainbus0 addr 0x1c800000 level 3: ns16550a, working fifo
                    113:     com0: console
                    114:     cpu0 at mainbus0: QED RM5200 CPU (0x28a0) Rev. 10.0 with built-in FPU Rev. 1.0
                    115:     cpu0: 48 TLB entries, 256MB max page size
                    116:     cpu0: 32KB/32B 2-way set-associative L1 instruction cache
                    117:     cpu0: 32KB/32B 2-way set-associative write-back L1 data cache
                    118:     mcclock0 at mainbus0 addr 0x10000070: mc146818 compatible time-of-day clock
                    119:     panel0 at mainbus0 addr 0x1f000000
                    120:     gt0 at mainbus0 addr 0x14000000
                    121:     pci0 at gt0
                    122:     pchb0 at pci0 dev 0 function 0: Galileo GT-64011 System Controller, rev 1
                    123:     pcib0 at pci0 dev 9 function 0
                    124:     pcib0: VIA Technologies VT82C586 PCI-ISA Bridge, rev 57
                    125:     viaide0 at pci0 dev 9 function 1
                    126:     viaide0: VIA Technologies VT82C586 (Apollo VP) ATA33 controller
                    127:     viaide0: primary channel interrupting at irq 14
                    128:     atabus0 at viaide0 channel 0
                    129:     viaide0: secondary channel interrupting at irq 15
                    130:     atabus1 at viaide0 channel 1
                    131:     wd0 at atabus0 drive 0
                    132:     wd0: <netbsd-cobalt.img>
                    133:     wd0: 750 MB, 1524 cyl, 16 head, 63 sec, 512 bytes/sect x 1536192 sectors
                    134: 
                    135: ### The bus\_space(9) framework
                    136: 
                    137: -   “The goal of the bus\_space functions is to allow a single driver
                    138:     source file to manipulate a set of devices on different system
                    139:     architectures, and to allow a single driver object file to
                    140:     manipulate a set of devices on multiple bus types on a single
                    141:     architecture.”
                    142: -   Provides a set of functions implementing common operations on the
                    143:     bus like mapping, reading, writing, copying, etc.
                    144: -   The bus\_space(9) is implemented at the machine-dependent level
                    145:     (typically it’s a part of architecture-specific code), but all
1.6       mspo      146:     implementations present the same interface
                    147: > At least they should, some functions are missing on less popular ports
1.1       mspo      148: 
                    149: ### Machine independent drivers
                    150: 
                    151: -   If possible drivers should work on any hardware platform
                    152: -   High quality, machine-independent (MI) drivers are an important
                    153:     factor that adds to NetBSD portability
                    154: -   Some drivers are completely MI, some have MD or bus dependent
                    155:     attachments and some are completely MD
                    156:     -   A driver for a typical PCI card will be completely MI
                    157:     -   A driver for the components of a SoC will usually be completely
                    158:         MD
                    159: -   The bus\_space abstraction helps to achieve portability,
                    160:     transparently handling endianness issues and hiding bus
                    161:     implementation details from the device driver
                    162: -   Even if we have MI drivers, writing the drivers is always
                    163:     significant part of effort needed to port NetBSD to new hardware
                    164: 
1.4       mspo      165: ## Example driver from scratch
1.1       mspo      166: 
                    167: ### Development environment
                    168: 
                    169: -   Out of scope of this course, but very well documented
                    170: -   Cross compiling is an easy task with the build.sh script
                    171: -   Described in [Part V of the NetBSD
                    172:     Guide](http://www.netbsd.org/docs/guide/en/part-compile.html)
                    173: -   Check out the NetBSD sources
1.6       mspo      174: -   $ build.sh -m cobalt tools
1.1       mspo      175:     will build compiler, assembler, linker, etc. for cobalt port
1.6       mspo      176: -   $ build.sh -m cobalt kernel=GENERIC
1.1       mspo      177:     will build the GENERIC kernel for cobalt
                    178: -   Call build.sh with a -u parameter to update (won’t rebuilding
                    179:     everything)
                    180: -   build.sh
                    181:     is calling nbconfig and nbmake tools, no magic involved
                    182: 
                    183: ### Quick introduction to GXemul
                    184: 
                    185: -   A framework for full-system computer architecture emulation,
                    186:     excellent for educational purposes
                    187: -   Capable of emulating several real machines supported by NetBSD
                    188: -   We’ll emulate a [Cobalt](http://en.wikipedia.org/wiki/Cobalt_Qube),
                    189:     MIPS-based micro server with PCI bus
                    190: -   I’ve modified GXemul and implemented an emulation of an additional
                    191:     PCI device
                    192: -   It will be used to show (almost) a real-life example of the driver
                    193:     development process
                    194: 
                    195: ### Our hardware - functional description
                    196: 
                    197: -   Business applications often use arithmetic operations like addition
                    198: -   Fake Cards Inc. responded to market needs and created a new product,
                    199:     Advanced Addition Accelerator
                    200: -   Pointy Haired Bosses will certainly buy it to accelerate their
                    201:     business applications, so let’s create a driver for NetBSD!
                    202: 
                    203: ### Our hardware - technical details
                    204: 
                    205: -   Overview
                    206:     -   Implemented as a PCI device
                    207:     -   Arithmetic unit capable of addition of two numbers
1.6       mspo      208:     -   Four registers in the PCI memory space
                    209: > Only three of these registers are of any importance for us at this moment
1.1       mspo      210: -   PCI configuration space
                    211:     -   Identified by the PCI vendor ID 0xfabc and product ID 0x0001
                    212:     -   Base Address Register 0x10 used to configure the engine address
                    213:     -   4 x 32-bit registers = 16 bytes
                    214:     -   Other configuration registers irrelevant
                    215: 
                    216: ### Our hardware - technical details (memory mapped register set)
                    217: 
                    218: -   Advanced Addition Acceleration registers
                    219: 
1.10      ryoon     220: [[!table data="""
                    221: Register Name  |Offset         |Description
                    222: COMMAND                |0x4            |Register used to issue commands to the engine
                    223: DATA           |0x8            |Register used to load data to internal engine registers
                    224: RESULT         |0xC            |Register used to store the result of arithmetic operation
                    225: """]]
1.1       mspo      226: 
                    227: -   COMMAND register
                    228: 
1.10      ryoon     229: [[!table data="""
                    230: Bit    |R/W    |Description
                    231: 0      |W      |Execute ADD operation on values loaded into internal register A and B
                    232: 1      |R/W    |Select internal register A for access through DATA register
                    233: 2      |R/W    |Select internal register B for access through DATA register
                    234: """]]
1.1       mspo      235: 
                    236: -   Selecting internal register A and B at the same time will lead to
                    237:     undefined behaviour
                    238: 
                    239: ### Our hardware - technical details (memory mapped register set)
                    240: 
                    241: -   DATA register
                    242: 
1.10      ryoon     243: [[!table data="""
                    244: Bit    |R/W    |Description
                    245: 0:31   |R/W    |Read/write the value in internal engine register
                    246: """]]
1.1       mspo      247: 
                    248: -   RESULT register
                    249: 
1.10      ryoon     250: [[!table data="""
                    251: Bit    |R/W    |Description
                    252: 0:31   |R      |Holds the result of last ADD operation
                    253: """]]
1.1       mspo      254: 
                    255: ### Our hardware - technical details (operation algorithm)
                    256: 
                    257: -   Select the internal register A for access (write 0x2 into COMMAND
                    258:     register)
                    259: -   Write the first number into DATA register
                    260: -   Select the internal register B for access (write 0x4 into COMMAND
                    261:     register)
                    262: -   Write the second number into DATA register
                    263: -   Issue the ADD operation (write 0x1 into COMMAND register)
                    264: -   Read the result from RESULT register
                    265: 
                    266: ### Adding a new driver to the NetBSD kernel
                    267: 
                    268: -   We’ll discuss the steps needed to add a new MI PCI device driver to
                    269:     the NetBSD kernel
                    270:     -   Add the vendor and device ID to the database of PCI IDs
                    271:     -   Create a set of the driver source files in
1.6       mspo      272:         src/sys/dev/$BUSNAME/
                    273:     -   Add the new driver to src/sys/dev/$BUSNAME/$BUSNAME.files file
                    274:     -   Add the new driver to DEVNAMES file
                    275: > Required if you are NetBSD developer, optional otherwise.
1.1       mspo      276: 
                    277: ### Modifying the PCI device database
                    278: 
                    279:     unmatched vendor 0xfabc product 0x0001 (Co-processor 
                    280:     processor, revision 0x01) at pci0 dev 12 function 0 
                    281:     not configured
                    282: 
                    283: -   The kernel does not know anything about this vendor and device
                    284: -   Add it to the PCI device database - src/sys/dev/pci/pcidevs
                    285: -   vendor VENDORNAME 0xVENDORID Long Vendor Name
                    286: -   product VENDORNAME PRODUCTNAME 0xPRODUCTID Long Product Name
                    287: -   To regenerate pcidevs\*.h run awk -f devlist2h.awk pcidevs or
                    288:     Makefile.pcidevs if you’re on NetBSD
                    289: 
                    290: ### Modifying the PCI device database - example
                    291: 
                    292:     --- pcidevs 29 Sep 2012 10:26:14 -0000  1.1139
                    293:     +++ pcidevs 5 Oct 2012 08:52:59 -0000
                    294:     @@ -669,6 +669,7 @@
                    295:      vendor CHRYSALIS   0xcafe  Chrysalis-ITS
                    296:      vendor MIDDLE_DIGITAL  0xdeaf  Middle Digital
                    297:      vendor ARC     0xedd8  ARC Logic
                    298:     +vendor FAKECARDS   0xfabc  Fake Cards
                    299:      vendor INVALID     0xffff  INVALID VENDOR ID
                    300:      
                    301:      /*
                    302:     @@ -2120,6 +2121,9 @@
                    303:      /* Eumitcom products */
                    304:      product EUMITCOM WL11000P  0x1100  WL11000P PCI WaveLAN/IEEE 802.11
                    305:      
                    306:     +/* FakeCards products */
                    307:     +product FAKECARDS AAA      0x0001  Advanced Addition Accelerator
                    308:     +
                    309:      /* O2 Micro */
                    310:      product O2MICRO 00F7       0x00f7  Integrated OHCI IEEE 1394 Host Controller
                    311:      product O2MICRO OZ6729     0x6729  OZ6729 PCI-PCMCIA Bridge
                    312: 
                    313: ### Modifying the PCI device database - example
                    314: 
                    315:     Fake Cards Advanced Addition Accelerator (Co-processor 
                    316:     processor, revision 0x01) at pci0 dev 12 function 0 
                    317:     not configured
                    318: 
                    319: -   Now the kernel knows the vendor and product ID
                    320: -   But there’s still no driver for this device
                    321: 
                    322: ### Adding the new PCI driver
                    323: 
                    324: -   Choose a name - short, easy to remember, avoid numbers
1.5       mspo      325:     -   faa looks like a good name, but you can choose any name you like
1.1       mspo      326: -   Create a set of new files in src/sys/dev/pci
                    327:     -   faa.c
                    328:         - main driver code
                    329:     -   faareg.h
1.6       mspo      330:         - register definitions
                    331: > Might not exist if the driver is only a simple passthrough from a specific bus to another MI driver.
1.1       mspo      332:     -   faavar.h
                    333:         - driver structures and functions used in other parts of the
1.6       mspo      334:         kernel
                    335: > Omitted if not needed.
1.1       mspo      336: -   Modify driver definitions
                    337:     -   src/sys/dev/pci/files.pci
                    338:     -   src/sys/dev/DEVNAMES
                    339: -   Configure the kernel to use the newly added driver -
1.6       mspo      340:     src/sys/arch/$PORTNAME/conf/GENERIC
1.1       mspo      341: 
                    342: ### Adding the new PCI driver - main driver
                    343: 
                    344: -   Kernel includes are at the beginning, followed by machine-specific
                    345:     and bus-specific includes
                    346: -   Should also include faareg.h and faavar.h files
                    347: -   A minimal driver needs just two functions
                    348:     -   faa\_match
                    349:         (or faa\_probe for some buses)
                    350:     -   faa\_attach
                    351: -   The CFATTACH\_DECL\_NEW macro plugs the above functions into
                    352:     autoconf(9) mechanism
                    353: 
                    354: ### Adding the new PCI driver - main driver
                    355: 
                    356: -   static int faa\_match(device\_t parent, cfdata\_t match, void
                    357:     \*aux);
                    358:     -   Check if the driver should attach to a given device (for example
                    359:         in case of PCI bus, it will be used to check vendor and product
                    360:         ID)
                    361:     -   parent
                    362:         - pointer to parent’s driver device structure
                    363:     -   match
                    364:         - pointer to autoconf(9) details structure
                    365:     -   aux
                    366:         - despite the name the most important argument, usually contains
                    367:         bus-specific structure describing device details
                    368: 
                    369: -   static void faa\_attach(device\_t parent, device\_t self, void
                    370:     \*aux);
                    371:     -   Attach the driver to a given device
                    372:     -   parent
                    373:         - same as with match function
                    374:     -   self
                    375:         - pointer to driver’s device structure
                    376:     -   aux
                    377:         - same as with match function
                    378: -   See definitions of these functions in the
                    379:     [driver(9)](http://netbsd.gw.com/cgi-bin/man-cgi?driver+9+NetBSD-current)
                    380:     man page.
                    381: 
                    382: ### Adding the new PCI driver - main driver cont’d
                    383: 
                    384: -   CFATTACH\_DECL\_NEW(faa, sizeof(struct faa\_softc), faa\_match,
                    385:     faa\_attach, NULL, NULL);
                    386:     -   driver name
                    387:     -   size of softc structure containing state of driver’s instance
                    388:     -   match/probe function
                    389:     -   attach function
                    390:     -   detach function
                    391:     -   activate function
                    392: -   The “\_NEW” name is unfortunate
                    393: -   Pass NULL for unimplemented functions
                    394: -   We won’t cover detach and activate now, as they are not needed for a
                    395:     simple driver
                    396: 
                    397: ### Adding the new PCI driver - main driver example
                    398: 
                    399: -   src/sys/dev/pci/faa.c
                    400: 
                    401: <!-- -->
                    402: 
                    403:     #include <sys/cdefs.h>
1.11    ! ryoon     404:     __KERNEL_RCSID(0, "$NetBSD: bus_space_tutorial.mdwn,v 1.10 2013/06/29 12:37:00 ryoon Exp $");
1.1       mspo      405:     #include <sys/param.h>
                    406:     #include <sys/device.h>
                    407:     #include <dev/pci/pcivar.h>
                    408:     #include <dev/pci/pcidevs.h>
                    409:     #include <dev/pci/faareg.h>
                    410:     #include <dev/pci/faavar.h>
                    411: 
                    412:     static int      faa_match(device_t, cfdata_t, void *);
                    413:     static void     faa_attach(device_t, device_t, void *);
                    414: 
                    415:     CFATTACH_DECL_NEW(faa, sizeof(struct faa_softc),
                    416:         faa_match, faa_attach, NULL, NULL);
                    417: 
                    418:     static int
                    419:     faa_match(device_t parent, cfdata_t match, void *aux)
                    420:     {
                    421:             return 0;
                    422:     }
                    423: 
                    424:     static void
                    425:     faa_attach(device_t parent, device_t self, void *aux)
                    426:     { 
                    427:     }
                    428: 
                    429: ### Adding the new PCI driver - auxiliary includes
                    430: 
                    431: -   src/sys/dev/pci/faareg.h
                    432: 
                    433: <!-- -->
                    434: 
                    435:     #ifndef FAAREG_H
                    436:     #define FAAREG_H
                    437:     /* 
                    438:      * Registers are defined using preprocessor:
                    439:      * #define FAA_REGNAME  0x0
                    440:      * We'll add them later, let's leave it empty for now.
                    441:      */
                    442:     #endif /* FAAREG_H */
                    443: 
                    444: -   src/sys/dev/pci/faavar.h
                    445: 
                    446: <!-- -->
                    447: 
                    448:     #ifndef FAAVAR_H
                    449:     #define FAAVAR_H
                    450: 
                    451:     /* sc_dev is an absolute minimum, we'll add more later */
                    452:     struct faa_softc {
                    453:             device_t sc_dev;
                    454:     };
                    455:     #endif /* FAAVAR_H */
                    456: 
                    457: ### Adding the new PCI driver - registering the driver (courtesy)
                    458: 
                    459: -   src/sys/dev/DEVNAMES
                    460: 
                    461: <!-- -->
                    462: 
                    463:     --- DEVNAMES    1 Sep 2012 11:19:58 -0000   1.279
                    464:     +++ DEVNAMES    6 Oct 2012 19:59:06 -0000
                    465:     @@ -436,6 +436,7 @@
                    466:      ex         MI
                    467:      exphy          MI
                    468:      ezload         MI      Attribute
                    469:     +faa            MI
                    470:      fb         luna68k
                    471:      fb         news68k
                    472:      fb         newsmips
                    473: 
                    474: ### Adding the new PCI driver - registering the driver
                    475: 
                    476: -   See config(5)
                    477: -   src/sys/dev/pci/files.pci
                    478: 
                    479: <!-- -->
                    480: 
                    481:     --- pci/files.pci   2 Aug 2012 00:17:44 -0000   1.360
                    482:     +++ pci/files.pci   6 Oct 2012 19:59:10 -0000
                    483:     @@ -1122,3 +1122,9 @@
                    484:      device tdvfb: wsemuldisplaydev, rasops8, vcons, videomode
                    485:      attach tdvfb at pci
                    486:      file   dev/pci/tdvfb.c     tdvfb   
                    487:     +
                    488:     +# FakeCards Advanced Addition Accelerator
                    489:     +device faa
                    490:     +attach faa at pci
                    491:     +file   dev/pci/faa.c       faa 
                    492:     +
                    493: 
                    494: ### Adding the new PCI driver to the kernel configuration
                    495: 
                    496: -   src/sys/arch/cobalt/conf/GENERIC
                    497: 
                    498: <!-- -->
                    499: 
                    500:     --- GENERIC 10 Mar 2012 21:51:50 -0000  1.134
                    501:     +++ GENERIC 6 Oct 2012 20:12:37 -0000
                    502:     @@ -302,6 +302,9 @@
                    503:      #fms*      at pci? dev ? function ?    # Forte Media FM801
                    504:      #sv*       at pci? dev ? function ?    # S3 SonicVibes
                    505:      
                    506:     +# Fake Cards Advanced Addition Accelerator
                    507:     +faa*       at pci? dev ? function ?
                    508:     +
                    509:      # Audio support
                    510:      #audio*        at audiobus?
                    511: 
                    512: -   The above definition means that an instance of faa may be attached
                    513:     to any PCI bus, any device, any function
                    514: -   The exact position of the rule in the configuration file is not
                    515:     important in this case
                    516: -   See
                    517:     [config(5)](http://netbsd.gw.com/cgi-bin/man-cgi?config+5+NetBSD-current)
                    518:     for a description of the device definition language
                    519: 
                    520: ### Adding the new PCI driver - example
                    521: 
                    522: -   The driver should compile now
                    523: -   The driver’s match function will check if the driver is able to work
                    524:     with a given device
                    525: -   Since it is not implemented, the kernel will not attach the driver
                    526: 
                    527: ### Matching the PCI device
                    528: 
                    529: -   Modify the faa\_match function to match the specified PCI device
                    530: -   Use PCI\_VENDOR and PCI\_PRODUCT macros to obtain the IDs
                    531: 
                    532: <!-- -->
                    533: 
                    534:     static int
                    535:     faa_match(device_t parent, cfdata_t match, void *aux)
                    536:     {
                    537:             const struct pci_attach_args *pa = (const struct pci_attach_args *)aux;
                    538: 
                    539:             if ((PCI_VENDOR(pa->pa_id) == PCI_VENDOR_FAKECARDS) 
                    540:                 && (PCI_PRODUCT(pa->pa_id) == PCI_PRODUCT_FAKECARDS_AAA))
                    541:                     return 1;
                    542: 
                    543:             return 0;
                    544:     }
                    545: 
                    546: ### Attaching to the PCI device
                    547: 
                    548:     faa0 at pci0 dev 12 function 0
                    549: 
                    550: -   The driver has successfully matched and attached to the PCI device
                    551:     but still is not doing anything useful
                    552: -   Let’s fill the attach function and actually program the hardware
                    553: 
                    554: ### Variable types used with bus\_space
                    555: 
                    556: -   bus\_space\_tag\_t
                    557: 
                    558:     – type used to describe a particular bus, usually passed to the
1.10      ryoon     559:        driver from MI bus structures
1.1       mspo      560: 
                    561: -   bus\_space\_handle\_t
                    562: 
                    563:     – used to describe a mapped range of bus space, usually created with
1.10      ryoon     564:        the bus\_space\_map() function
1.1       mspo      565: 
                    566: -   bus\_addr\_t
                    567: 
                    568:     – address on the bus
                    569: 
                    570: -   bus\_size\_t
                    571: 
                    572:     – an amount of space on the bus
                    573: 
                    574: -   Contents of these types are MD, so avoid modifying from within the
1.6       mspo      575:     driver
                    576: > although you’ll often have to use bus\_size\_t
1.1       mspo      577: 
                    578: ### Why do we need to “map” the resources?
                    579: 
                    580: -   “The bus space must be mapped before it can be used, and should be
                    581:     unmapped when it is no longer needed”
                    582: -   It’s a machine-dependent process but it’s also conveniently hidden
                    583:     from the programmer by the bus\_space framework
                    584: 
                    585: ### Mapping the hardware resources
                    586: 
                    587: -   The generic bus\_space(9) way to map space
                    588: 
                    589: <!-- -->
                    590: 
                    591:     bus_space_map(bus_space_tag_t space, bus_addr_t address, 
                    592:     bus_size_t size, int flags, bus_space_handle_t  *handlep);
                    593: 
                    594: -   bus\_space\_map
                    595: 
1.10      ryoon     596:     – creates a mapping from the physical address to a kernel virtual
1.1       mspo      597:     address
                    598: 
                    599: -   space
                    600: 
                    601:     – represents the bus on which the mapping will be created
                    602: 
                    603: -   address
                    604: 
                    605:     – typically represents the physical address for which a mapping will
1.10      ryoon     606:        be created
1.1       mspo      607: 
                    608: -   size
                    609: 
                    610:     – describes the amount of bus space to be mapped
                    611: 
                    612: -   handlep
                    613: 
                    614:     – pointer to mapped space (filled after successful mapping)
                    615: 
                    616: -   Separate space and address
                    617: 
                    618: ### Mapping the hardware resources
                    619: 
                    620: -   The PCI-specific way to map space
                    621: 
                    622: <!-- -->
                    623: 
                    624:     pci_mapreg_map(const struct pci_attach_args *pa, int reg, pcireg_t type, 
                    625:     int busflags, bus_space_tag_t *tagp, bus_space_handle_t *handlep, 
                    626:     bus_addr_t *basep, bus_size_t *sizep);
                    627: 
                    628: -   pci\_mapreg\_map
                    629: 
1.10      ryoon     630:     – creates mapping from physical address present in specified BAR
1.1       mspo      631:     register to kernel virtual address
                    632: 
                    633: -   pa
                    634: 
                    635:     – struct describing PCI attachment details (passed through aux)
                    636: 
                    637: -   reg
                    638: 
                    639:     – BAR register number
                    640: 
                    641: -   type
                    642: 
                    643:     – Select mapping type (I/O, memory)
                    644: 
                    645: -   busflags
                    646: 
1.10      ryoon     647:     – Passed to bbus_space_map flags argument
1.1       mspo      648: 
                    649: -   tagp
                    650: 
1.11    ! ryoon     651:     – pointer to bus_pace_tag
1.1       mspo      652: 
                    653: -   handlep
                    654: 
                    655:     – pointer to a mapped space
                    656: 
                    657: -   basep
                    658: 
                    659:     – address of a mapped space
                    660: 
                    661: -   sizep
                    662: 
                    663:     – size of mapped space (equivalent to BAR size)
                    664: 
                    665: -   The last four parameters are filled after successful mapping
                    666: 
                    667: ### Mapping the registers using BAR - adding auxiliary includes
                    668: 
                    669: -   src/sys/dev/pci/faareg.h
                    670: 
                    671: <!-- -->
                    672: 
                    673:     #define FAA_MMREG_BAR   0x10
                    674: 
                    675: -   src/sys/dev/pci/faavar.h
                    676: 
                    677: <!-- -->
                    678: 
                    679:     struct faa_softc {
                    680:             device_t sc_dev;
                    681: 
                    682:             bus_space_tag_t sc_regt;
                    683:             bus_space_handle_t sc_regh;
                    684:             bus_addr_t sc_reg_pa;
                    685: 
                    686:     };
                    687: 
                    688: ### Mapping the registers using BAR - main driver code
                    689: 
                    690: -   src/sys/dev/pci/faa.c
                    691: 
                    692: <!-- -->
                    693: 
                    694:     static void
                    695:     faa_attach(device_t parent, device_t self, void *aux)
                    696:     {
                    697:             struct faa_softc *sc = device_private(self);
                    698:             const struct pci_attach_args *pa = aux;
                    699: 
                    700:             sc->sc_dev = self;
                    701: 
                    702:             pci_aprint_devinfo(pa, NULL);
                    703: 
                    704:             if (pci_mapreg_map(pa, FAA_MMREG_BAR, PCI_MAPREG_TYPE_MEM, 0, 
                    705:                 &sc->sc_regt, &sc->sc_regh, &sc->sc_reg_pa, 0) != 0 ) {
                    706:                 aprint_error_dev(sc->sc_dev, "can't map the BAR\n");
                    707:                 return;
                    708:             }
                    709: 
                    710:             aprint_normal_dev(sc->sc_dev, "regs at 0x%08x\n", (uint32_t) sc->sc_reg_pa);
                    711:     }
                    712: 
                    713: ### Accessing the hardware registers
                    714: 
                    715: -   The bus\_space\_read\_ and bus\_space\_write\_ functions are basic
                    716:     methods of reading and writing the hardware registers
                    717: 
                    718: -   uintX\_t bus\_space\_read\_X(bus\_space\_tag\_t space,
                    719:     bus\_space\_handle\_t handle, bus\_size\_t offset);
                    720: 
                    721: -   void bus\_space\_write\_X(bus\_space\_tag\_t space,
                    722:     bus\_space\_handle\_t handle, bus\_size\_t offset, uintX\_t value);
                    723: 
                    724:     -   space
                    725: 
                    726:         - tag describing the bus
                    727: 
                    728:     -   handle
                    729: 
                    730:         - describes the exact location on the bus where read/write
                    731:         should occur, this handle is obtained by bus\_space\_map
                    732: 
                    733:     -   offset
                    734: 
                    735:         - offset from handle location
                    736: 
                    737:     -   The read function returns the data read from the specified
                    738:         location, while write has an argument value which should be
                    739:         filled with data to be written
                    740: 
                    741: ### Variants of bus\_space\_read and bus\_space\_write
                    742: 
1.10      ryoon     743: [[!table data="""
                    744: Data   |Read function          |Write function
                    745: 8-bitb |bus_space_read_1       |bus_space_write_1
                    746: 16-bit |bus_space_read_2       |bus_space_write_2
                    747: 32-bit |bus_space_read_4       |bus_space_write_4
                    748: 64-bit |bus_space_read_8       |bus_space_write_8
                    749: """]]
1.1       mspo      750: 
                    751: -   There are many more variants of read and write functions and they
                    752:     are useful in certain situations, see the
                    753:     [bus\_space(9)](http://netbsd.gw.com/cgi-bin/man-cgi?bus_space++NetBSD-current)
                    754:     man page
                    755: 
                    756: ### Accessing the hardware registers - example
                    757: 
                    758: -   Create a function that will write a value into the DATA register of
                    759:     our device, then read it back and check if the value is the same as
                    760:     written
                    761: 
                    762: -   Define the DATA register in the driver
                    763: 
                    764: -   src/sys/dev/pci/faareg.h
                    765: 
                    766: <!-- -->
                    767: 
                    768:     #define FAA_DATA                0x8
                    769:     #define FAA_COMMAND             0x4
                    770:     #define FAA_COMMAND_STORE_A         __BIT(1)
                    771: 
                    772: -   Define the new function in main driver code
                    773: 
                    774: -   static bool faa\_check(struct faa\_softc \*sc);
                    775: 
                    776: ### Accessing the hardware registers - example
                    777: 
                    778: -   src/sys/dev/pci/faa.c
                    779: 
                    780: <!-- -->
                    781: 
                    782:     static void
                    783:     faa_attach(device_t parent, device_t self, void *aux)
                    784:     {
                    785:        /* ... */
                    786:        if (!faa_check(sc)) {
                    787:             aprint_error_dev(sc->sc_dev, "hardware not responding\n");
                    788:             return;
                    789:        }
                    790:     }
                    791: 
                    792:     static bool
                    793:     faa_check(struct faa_softc *sc)
                    794:     {
                    795:             uint32_t testval = 0xff11ee22; 
                    796:             bus_space_write_4(sc->sc_regt, sc->sc_regh, FAA_COMMAND, FAA_COMMAND_STORE_A);
                    797:             bus_space_write_4(sc->sc_regt, sc->sc_regh, FAA_DATA, testval);
                    798:             if (bus_space_read_4(sc->sc_regt, sc->sc_regh, FAA_DATA) == testval)
                    799:                     return true;
                    800: 
                    801:             return false;
                    802:     }
                    803: 
                    804: ### Accessing the hardware registers - running the example
                    805: 
                    806: -   Update the kernel binary and run it again
                    807: 
                    808: -   Check the GXemul log
                    809: 
                    810: <!-- -->
                    811: 
                    812:     [ faa: COMMAND register (0x4) WRITE value 0x2 ]
                    813:     [ faa: DATA register (0x8) WRITE value 0xff11ee22 ]
                    814:     [ faa: DATA register (0x8) READ value 0xff11ee22 ]
                    815: 
                    816: -   GXemul will conveniently display all accesses to our device
                    817: 
                    818: -   The faa driver still does attach without error, which means that the
                    819:     check function is working properly
                    820: 
                    821: <!-- -->
                    822: 
                    823:     faa0 at pci0 dev 12 function 0: Fake Cards Advanced Addition Accelerator (rev. 0x01)
                    824:     faa0: registers at 0x10110000
                    825: 
                    826: ### Implementing addition using the hardware
                    827: 
                    828: -   The basic principle of device operation should be laid out in the
                    829:     data sheet
                    830: 
                    831: -   We need to implement an algorithm based on this description
                    832: 
                    833: -   Writing such an algorithm is often not needed, since the NetBSD
                    834:     kernel already has frameworks for common device types (such as
                    835:     atabus/wd for IDE and SATA hard disk controllers, wsdisplay/wscons
                    836:     for frame buffers, etc.)
                    837: 
                    838: ### Implementing addition using the hardware
                    839: 
                    840: -   Define all registers
                    841: 
                    842: -   src/sys/dev/pci/faareg.h
                    843: 
                    844: <!-- -->
                    845: 
                    846:     #define FAA_STATUS              0x0
                    847:     #define FAA_COMMAND             0x4
                    848:     #define FAA_COMMAND_ADD             __BIT(0)        
                    849:     #define FAA_COMMAND_STORE_A         __BIT(1)
                    850:     #define FAA_COMMAND_STORE_B         __BIT(2)
                    851:     #define FAA_DATA                0x8
                    852:     #define FAA_RESULT              0xC
                    853: 
                    854: ### Implementing addition using the hardware
                    855: 
                    856: -   Add a new function to the main driver code
                    857: 
                    858: -   src/sys/dev/pci/faa.c
                    859: 
                    860: <!-- -->
                    861: 
                    862:     static void
                    863:     faa_attach(device_t parent, device_t self, void *aux)
                    864:     {
                    865:             /* ... */
                    866:             aprint_normal_dev(sc->sc_dev, "just checking: 1 + 2 = %d\n", faa_add(sc, 1, 2));
                    867:     }
                    868: 
                    869:     static uint32_t
                    870:     faa_add(struct faa_softc *sc, uint32_t a, uint32_t b)
                    871:     {
                    872:             bus_space_write_4(sc->sc_regt, sc->sc_regh, FAA_COMMAND, FAA_COMMAND_STORE_A);
                    873:             bus_space_write_4(sc->sc_regt, sc->sc_regh, FAA_DATA, a);
                    874:             bus_space_write_4(sc->sc_regt, sc->sc_regh, FAA_COMMAND, FAA_COMMAND_STORE_B);
                    875:             bus_space_write_4(sc->sc_regt, sc->sc_regh, FAA_DATA, b);
                    876:             bus_space_write_4(sc->sc_regt, sc->sc_regh, FAA_COMMAND, FAA_COMMAND_ADD);
                    877:             return bus_space_read_4(sc->sc_regt, sc->sc_regh, FAA_RESULT);
                    878:     }
                    879: 
                    880: ### Implementing addition using the hardware - running the example
                    881: 
                    882: -   Update the kernel binary and run it again
                    883: 
                    884: -   Check GXemul log
                    885: 
                    886: <!-- -->
                    887: 
                    888:     [ faa: COMMAND register (0x4) WRITE value 0x2 ]
                    889:     [ faa: DATA register (0x8) WRITE value 0x1 ]
                    890:     [ faa: COMMAND register (0x4) WRITE value 0x4 ]
                    891:     [ faa: DATA register (0x8) WRITE value 0x2 ]
                    892:     [ faa: COMMAND register (0x4) WRITE value 0x1 ]
                    893:     [ faa: RESULT register (0xC) READ value 0x3 ]
                    894: 
                    895: -   Looks like it worked!
                    896: 
                    897: <!-- -->
                    898: 
                    899:     faa0 at pci0 dev 12 function 0: Fake Cards Advanced Addition Accelerator (rev. 0x01)
                    900:     faa0: registers at 0x10110000
                    901:     faa0: just checking: 1 + 2 = 3
                    902: 
1.3       mspo      903: ## Interacting with userspace
1.1       mspo      904: 
                    905: ### The kernel-user space interface
                    906: 
                    907: -   Now that the core functionality of the kernel driver is working, it
                    908:     should be exposed to user space
                    909: -   The interface between kernel driver and userspace can be designed in
                    910:     many different ways
                    911: -   The classic UNIX way of interfacing between the kernel and user
                    912:     space is a device file
                    913: -   Even when using device files there is no single interfacing method
                    914:     that fits all use cases
                    915: -   It’s up to the programmer to define the communication protocol
                    916: 
                    917: ### Device files
                    918: 
                    919: -   crw-r—– 1 root wheel 101, 1 Aug 12 21:53 /dev/file
                    920: -   The kernel identifies which driver should service the request to
                    921:     this file by using major and minor numbers (101 and 1 in the example
                    922:     above)
                    923: -   The major number identifies the driver
                    924: -   The minor number usually identifies the driver instance, although
                    925:     the driver is free to use it in any other way
                    926: -   In NetBSD device files are created statically
                    927:     -   By the MAKEDEV script during installation or boot
                    928:     -   Manually by using the mknod utility
                    929: 
                    930: ### Operations on device files
                    931: 
                    932: -   [open(2)](http://netbsd.gw.com/cgi-bin/man-cgi?read++NetBSD-current)
                    933:     and
                    934:     [close(2)](http://netbsd.gw.com/cgi-bin/man-cgi?read++NetBSD-current)
                    935: -   [read(2)](http://netbsd.gw.com/cgi-bin/man-cgi?read++NetBSD-current)
                    936:     and
                    937:     [write(2)](http://netbsd.gw.com/cgi-bin/man-cgi?write++NetBSD-current)
                    938: -   [ioctl(2)](http://netbsd.gw.com/cgi-bin/man-cgi?write++NetBSD-current)
                    939: -   [poll(2)](http://netbsd.gw.com/cgi-bin/man-cgi?poll++NetBSD-current)
                    940: -   [mmap(2)](http://netbsd.gw.com/cgi-bin/man-cgi?write++NetBSD-current)
                    941: -   and more…
                    942: -   Any mix of the above system calls might be used to interface between
                    943:     the kernel and user space
                    944: -   We’ll implement an ioctl(2)-based communication mechanism
                    945: 
                    946: ### Adding cdevsw
                    947: 
                    948: -   cdevsw
                    949: 
                    950:     is used to decide which operation on the character device file calls
                    951:     which driver function
                    952: 
                    953: -   Not all calls have to be implemented, although some device layers
                    954:     define a set of calls that a driver must implement
                    955: 
                    956: -   For example disk drivers must implement open, close, read, write and
                    957:     ioctl
                    958: 
                    959: -   src/sys/dev/pci/faa.c
                    960: 
                    961: <!-- -->
                    962: 
                    963:     dev_type_open(faaopen);
                    964:     dev_type_close(faaclose);
                    965:     dev_type_ioctl(faaioctl);
                    966: 
                    967:     const struct cdevsw faa_cdevsw = {
                    968:             faaopen, faaclose, noread, nowrite, faaioctl,
                    969:             nostop, notty, nopoll, nommap, nokqfilter, D_OTHER
                    970:     };
                    971: 
                    972: ### Prototyping the cdevsw operations
                    973: 
                    974: -   The dev\_type\* macros are used to prototype the functions passed to
                    975:     cdevsw
                    976: -   Pass no followed by a function name to the appropriate cdevsw field
                    977:     if it is not implemented
                    978: -   There’s also bdevsw for block devices, but we won’t use it in this
                    979:     example
                    980: -   The last member of the cdevsw structure defines the device flags,
                    981:     originally it was used to define the device type (still used for
                    982:     disks, tape drives and ttys, for other devices pass D\_OTHER)
                    983: 
                    984: ### Implemeting the cdevsw operations - open / close
                    985: 
                    986: -   src/sys/dev/pci/faa.c
                    987: 
                    988: <!-- -->
                    989: 
                    990:     int
                    991:     faaopen(dev_t dev, int flags, int mode, struct lwp *l)
                    992:     {
                    993:             struct faa_softc *sc;
                    994:             sc = device_lookup_private(&faa_cd, minor(dev));
                    995: 
                    996:             if (sc == NULL)
                    997:                     return ENXIO;
                    998:             if (sc->sc_flags & FAA_OPEN)
                    999:                     return EBUSY;
                   1000: 
                   1001:             sc->sc_flags |= FAA_OPEN;
                   1002:             return 0;
                   1003:     }
                   1004:     int
                   1005:     faaclose(dev_t dev, int flag, int mode, struct lwp *l)
                   1006:     {
                   1007:             struct faa_softc *sc;
                   1008:             sc = device_lookup_private(&faa_cd, minor(dev));
                   1009: 
                   1010:             if (sc->sc_flags & FAA_OPEN)
                   1011:                     sc->sc_flags =~ FAA_OPEN;
                   1012: 
                   1013:             return 0;
                   1014:     }
                   1015: 
                   1016: ### Defining the ioctls
                   1017: 
                   1018: -   ioctl(2)
                   1019: 
                   1020:     can be used to call kernel-level functions and exchange data between
                   1021:     the kernel and user space
                   1022: 
                   1023: -   The classic way of passing data is by using structures, their
                   1024:     definitions are shared between the kernel and user space code
                   1025: -   The driver might support more than one ioctl, the \_IO\* macros are
                   1026:     used to define the operation and associated structure used to
                   1027:     exchange data
                   1028: 
                   1029:     -   \_IO
                   1030: 
                   1031:         - just a kernel function call, no data exchange
                   1032: 
                   1033:     -   \_IOR
                   1034: 
                   1035:         - kernel function call and data pass from kernel to user space
                   1036: 
                   1037:     -   \_IOW
                   1038: 
                   1039:         - kernel function call and data pass from user space to kernel
                   1040: 
                   1041:     -   \_IOWR
                   1042: 
                   1043:         - kernel function call and data exchange in both directions
                   1044: 
                   1045:     -   \#define DRIVERIO\_IOCTLNAME \_IOXXX(group, ioctl\_number, data
                   1046:         structure)
                   1047: 
1.3       mspo     1048: ## Using ioctls
1.1       mspo     1049: 
                   1050: ### Defining the ioctls
                   1051: 
                   1052: -   src/sys/dev/pci/faaio.h
                   1053: 
                   1054: <!-- -->
                   1055: 
                   1056:     #include <sys/ioccom.h>
                   1057:                          
                   1058:     #define FAAIO_ADD   _IOWR(0, 1, struct faaio_add)
                   1059: 
                   1060:     struct faaio_add {
                   1061:         uint32_t a;
                   1062:         uint32_t b;
                   1063:         uint32_t *result;
                   1064:     };
                   1065: 
                   1066: -   In the above example the ioctl group is not defined (0), but a
                   1067:     single letter identifier could appear as first argument to \_IOWR
                   1068: 
                   1069: ### Implemeting the cdevsw operations - ioctl
                   1070: 
                   1071: -   src/sys/dev/pci/faa.c
                   1072: 
                   1073: <!-- -->
                   1074: 
                   1075:     int
                   1076:     faaioctl(dev_t dev, u_long cmd, void *data, int flag, struct lwp *l)
                   1077:     {
                   1078:             struct faa_softc *sc = device_lookup_private(&faa_cd, minor(dev));
                   1079:             int err;
                   1080: 
                   1081:             switch (cmd) {
                   1082:             case FAAIO_ADD:
                   1083:                     err = faaioctl_add(sc, (struct faaio_add *) data);
                   1084:                     break;
                   1085:             default:
                   1086:                     err = EINVAL;
                   1087:                     break;
                   1088:             }
                   1089:             return(err);
                   1090:     }
                   1091:     static int
                   1092:     faaioctl_add(struct faa_softc *sc, struct faaio_add *data)
                   1093:     {
                   1094:             uint32_t result; int err;
                   1095: 
                   1096:             aprint_normal_dev(sc->sc_dev, "got ioctl with a %d, b %d\n",
                   1097:                 data->a, data->b);
                   1098: 
                   1099:             result = faa_add(sc, data->a, data->b);
                   1100:             err = copyout(&result, data->result, sizeof(uint32_t));
                   1101:             return err;
                   1102:     }
                   1103: 
                   1104: ### Using copyout to pass data to userspace
                   1105: 
                   1106: -   The copy(9) functions are used to copy kernel space data from/to
                   1107:     user space
                   1108: -   copyout(kernel\_address, user space\_address, size);
                   1109: -   Actually on Cobalt we could just do data-\>result = faa\_add();
                   1110:     instead of calling the copyout function, but that is a bad idea
                   1111: -   Some architectures (such as sparc64) have totally separate kernel
                   1112:     and user address spaces $ \implies $ user space addresses are
                   1113:     meaningless in the kernel
                   1114: 
                   1115: ### Defining device major number
                   1116: 
                   1117: -   Device major numbers for hardware drivers are usually defined in a
1.6       mspo     1118:     per-port manner
                   1119: > It’s also possible to define a major in a machine-independent way in src/sys/conf/majors
                   1120: -   src/sys/arch/$PORTNAME/conf/majors.$PORTNAME
1.1       mspo     1121: -   src/sys/arch/cobalt/conf/majors.cobalt
                   1122: -   The following defines a new character device file called /dev/faa\*
                   1123:     with major number 101, but only if the faa driver is included in the
                   1124:     kernel (last argument)
                   1125: -   device-major faa char 101 faa
                   1126: 
                   1127: ### Creating the device node
                   1128: 
                   1129: -   The mknod utility can be used to create the device file manually
                   1130: -   The driver name can be specified instead of the major number - it
                   1131:     will be automatically resolved into the correct major number
                   1132: -   mknod name [b | c] [major | driver] minor
                   1133: -   mknod /dev/faa0 c faa 0
                   1134: -   Created successfully
                   1135: -   crw-r–r– 1 root wheel 101, 0 Oct 8 2012 /dev/faa0
                   1136: 
                   1137: ### An example user space program
                   1138: 
                   1139: -   The example program will open the device file and call ioctl(2) on
                   1140:     it
                   1141: -   As simple as possible, just to show how communication is done
                   1142: -   Using ioctls from the user space
                   1143:     -   Open the device file with O\_RDWR
                   1144:     -   Call ioctl(2) with the operation number and structure as
                   1145:         parameters
                   1146: 
                   1147: ### An example user space program - source
                   1148: 
                   1149:     void add(int, uint32_t, uint32_t);
                   1150: 
                   1151:     static const char* faa_device = "/dev/faa0";
                   1152: 
                   1153:     int
                   1154:     main(int argc, char *argv[])
                   1155:     {
                   1156:             int devfd;
                   1157: 
                   1158:             if (argc != 3) {
                   1159:                     printf("usage: %s a b\n", argv[0]);
                   1160:                     return 1;
                   1161:             }
                   1162:             if ( (devfd = open(faa_device, O_RDWR)) == -1) {
                   1163:                     perror("can't open device file");
                   1164:                     return 1;
                   1165:             }
                   1166: 
                   1167:             add(devfd, atoi(argv[1]), atoi(argv[2]));
                   1168: 
                   1169:             close(devfd);
                   1170:             return 0;
                   1171:     }
                   1172: 
                   1173: ### An example user space program - source
                   1174: 
                   1175:     void
                   1176:     add(int devfd, uint32_t a, uint32_t b)
                   1177:     {
                   1178:             struct faaio_add faaio;
                   1179:             uint32_t result = 0;
                   1180: 
                   1181:             faaio.result = &result;
                   1182:             faaio.a = a;
                   1183:             faaio.b = b;
                   1184: 
                   1185:             if (ioctl(devfd, FAAIO_ADD, &faaio) == -1) {
                   1186:                     perror("ioctl failed");
                   1187:             }
                   1188:             printf("%d\n", result);
                   1189:     }
                   1190: 
                   1191: ### An example user space program - running it
                   1192: 
                   1193:     # make
                   1194:     cc -o aaa_add aaa_add.c
                   1195:     # ./aaa_add 3 7
                   1196:     faa0: got ioctl with a 3, b 7
                   1197:     10
                   1198: 
                   1199: -   The program is successfully accessing the faa driver through the
                   1200:     ioctl
                   1201: -   The faa0:... line is a kernel message, normally only seen on the
                   1202:     console terminal
                   1203: 
1.3       mspo     1204: ## A few tips
1.1       mspo     1205: 
                   1206: ### Avoiding common pitfalls
                   1207: 
                   1208: -   Always free resources allocated in the match or probe functions
                   1209: -   Always use bus\_space methods, don’t access the hardware using a
                   1210:     pointer dereference
                   1211: -   If possible test on more than one hardware architecture, some bugs
                   1212:     may surface
                   1213: -   Don’t reinvent the wheel, try to use existing kernel frameworks as
                   1214:     much as possible
                   1215: -   Use copy(9) (or uiomove(9) or store(9)/fetch(9)) to move data
                   1216:     between the kernel and user space
                   1217: 
                   1218: ### Basic driver debugging
                   1219: 
                   1220: -   Use aprint\_debug to print debug-level messages on console and log
                   1221:     them (enabled by passing AB\_DEBUG from the boot loader)
                   1222: -   Use the built-in DDB debugger
                   1223:     -   Enabled by the kernel option DDB
                   1224:     -   A kernel panic will start DDB if the DDB\_ONPANIC=1 kernel
                   1225:         option is specified or the ddb.onpanic sysctl is set to 1.
                   1226:     -   Run \# sysctl -w kern.panic\_now=1 to trigger a panic manually
                   1227:         (DIAGNOSTIC option)
                   1228: -   Remote debugging is possible on some ports
                   1229:     -   With KGDB through the serial port
                   1230:     -   With IPKDB through the network
                   1231: 
1.3       mspo     1232: ## Summary
1.1       mspo     1233: 
                   1234: ### Further reading
                   1235: 
                   1236: -   Documentation, articles:
                   1237:     -   [A Machine-Independent DMA Framework for NetBSD, Jason R.
                   1238:         Thorpe](http://www.netbsd.org/docs/kernel/bus_dma.pdf)
                   1239:     -   [Writing Drivers for NetBSD, Jochen
                   1240:         Kunz](ftp://ftp.netbsd.org/pub/NetBSD/misc/ddwg/NetBSD-driver_writing-1.0.1e.pdf)
                   1241:     -   [NetBSD Documentation: Writing a pseudo
                   1242:         device](http://www.netbsd.org/docs/kernel/pseudo/)
                   1243:     -   [autoconf(9)](http://netbsd.gw.com/cgi-bin/man-cgi?autoconf+9+NetBSD-current),
                   1244:         [bus\_space(9)](http://netbsd.gw.com/cgi-bin/man-cgi?bus_space+9+NetBSD-current)
                   1245:         [bus\_dma(9)](http://netbsd.gw.com/cgi-bin/man-cgi?bus_dma+9+NetBSD-current)
                   1246:         [driver(9)](http://netbsd.gw.com/cgi-bin/man-cgi?driver+9+NetBSD-current),
                   1247:         [pci(9)](http://netbsd.gw.com/cgi-bin/man-cgi?pci+9+NetBSD-current)
                   1248:         man pages, etc.
                   1249: 
                   1250: -   Example source code of drivers:
                   1251:     -   tdvfb
                   1252: 
1.4       mspo     1253:         voodoofb are fairly good frame buffer driver examples with
1.1       mspo     1254:         documentation publicly available.
                   1255: 
                   1256:     -   etsec
                   1257: 
                   1258:         is a nice example of a more complicated network interface driver
                   1259: 
                   1260: ### Get the source code
                   1261: 
                   1262: -   Download the source code and materials for this tutorial
                   1263: -   <https://github.com/rkujawa/busspace-tutorial>
                   1264: -   <https://github.com/rkujawa/gxemul-tutorial>
                   1265: 
                   1266: 
                   1267: 
                   1268: 
                   1269: 
                   1270: 
                   1271: 

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