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Linus Torvalds1da177e2005-04-16 15:20:36 -07001
Grant Grundler74da15e2006-12-25 01:06:35 -07002 How To Write Linux PCI Drivers
3
4 by Martin Mares <mj@ucw.cz> on 07-Feb-2000
5 updated by Grant Grundler <grundler@parisc-linux.org> on 23-Dec-2006
Linus Torvalds1da177e2005-04-16 15:20:36 -07006
7~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Grant Grundler74da15e2006-12-25 01:06:35 -07008The world of PCI is vast and full of (mostly unpleasant) surprises.
9Since each CPU architecture implements different chip-sets and PCI devices
10have different requirements (erm, "features"), the result is the PCI support
11in the Linux kernel is not as trivial as one would wish. This short paper
12tries to introduce all potential driver authors to Linux APIs for
13PCI device drivers.
14
15A more complete resource is the third edition of "Linux Device Drivers"
16by Jonathan Corbet, Alessandro Rubini, and Greg Kroah-Hartman.
17LDD3 is available for free (under Creative Commons License) from:
18
19 http://lwn.net/Kernel/LDD3/
20
21However, keep in mind that all documents are subject to "bit rot".
22Refer to the source code if things are not working as described here.
23
24Please send questions/comments/patches about Linux PCI API to the
25"Linux PCI" <linux-pci@atrey.karlin.mff.cuni.cz> mailing list.
26
Linus Torvalds1da177e2005-04-16 15:20:36 -070027
28
290. Structure of PCI drivers
30~~~~~~~~~~~~~~~~~~~~~~~~~~~
Grant Grundler74da15e2006-12-25 01:06:35 -070031PCI drivers "discover" PCI devices in a system via pci_register_driver().
32Actually, it's the other way around. When the PCI generic code discovers
33a new device, the driver with a matching "description" will be notified.
34Details on this below.
35
36pci_register_driver() leaves most of the probing for devices to
37the PCI layer and supports online insertion/removal of devices [thus
38supporting hot-pluggable PCI, CardBus, and Express-Card in a single driver].
39pci_register_driver() call requires passing in a table of function
40pointers and thus dictates the high level structure of a driver.
41
42Once the driver knows about a PCI device and takes ownership, the
43driver generally needs to perform the following initialization:
Linus Torvalds1da177e2005-04-16 15:20:36 -070044
45 Enable the device
Grant Grundler74da15e2006-12-25 01:06:35 -070046 Request MMIO/IOP resources
47 Set the DMA mask size (for both coherent and streaming DMA)
48 Allocate and initialize shared control data (pci_allocate_coherent())
49 Access device configuration space (if needed)
50 Register IRQ handler (request_irq())
51 Initialize non-PCI (i.e. LAN/SCSI/etc parts of the chip)
52 Enable DMA/processing engines
53
54When done using the device, and perhaps the module needs to be unloaded,
55the driver needs to take the follow steps:
56 Disable the device from generating IRQs
57 Release the IRQ (free_irq())
58 Stop all DMA activity
59 Release DMA buffers (both streaming and coherent)
60 Unregister from other subsystems (e.g. scsi or netdev)
61 Release MMIO/IOP resources
Linus Torvalds1da177e2005-04-16 15:20:36 -070062 Disable the device
63
Grant Grundler74da15e2006-12-25 01:06:35 -070064Most of these topics are covered in the following sections.
65For the rest look at LDD3 or <linux/pci.h> .
Linus Torvalds1da177e2005-04-16 15:20:36 -070066
67If the PCI subsystem is not configured (CONFIG_PCI is not set), most of
Grant Grundler74da15e2006-12-25 01:06:35 -070068the PCI functions described below are defined as inline functions either
69completely empty or just returning an appropriate error codes to avoid
70lots of ifdefs in the drivers.
Linus Torvalds1da177e2005-04-16 15:20:36 -070071
72
Linus Torvalds1da177e2005-04-16 15:20:36 -070073
Grant Grundler74da15e2006-12-25 01:06:35 -0700741. pci_register_driver() call
75~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
76
77PCI device drivers call pci_register_driver() during their
78initialization with a pointer to a structure describing the driver
79(struct pci_driver):
80
81 field name Description
82 ---------- ------------------------------------------------------
Linus Torvalds1da177e2005-04-16 15:20:36 -070083 id_table Pointer to table of device ID's the driver is
84 interested in. Most drivers should export this
85 table using MODULE_DEVICE_TABLE(pci,...).
Grant Grundler74da15e2006-12-25 01:06:35 -070086
87 probe This probing function gets called (during execution
88 of pci_register_driver() for already existing
89 devices or later if a new device gets inserted) for
90 all PCI devices which match the ID table and are not
91 "owned" by the other drivers yet. This function gets
92 passed a "struct pci_dev *" for each device whose
93 entry in the ID table matches the device. The probe
94 function returns zero when the driver chooses to
95 take "ownership" of the device or an error code
96 (negative number) otherwise.
97 The probe function always gets called from process
98 context, so it can sleep.
99
100 remove The remove() function gets called whenever a device
101 being handled by this driver is removed (either during
102 deregistration of the driver or when it's manually
103 pulled out of a hot-pluggable slot).
104 The remove function always gets called from process
105 context, so it can sleep.
106
Linus Torvalds1da177e2005-04-16 15:20:36 -0700107 suspend Put device into low power state.
Grant Grundler74da15e2006-12-25 01:06:35 -0700108 suspend_late Put device into low power state.
109
110 resume_early Wake device from low power state.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700111 resume Wake device from low power state.
Grant Grundler74da15e2006-12-25 01:06:35 -0700112
113 (Please see Documentation/power/pci.txt for descriptions
114 of PCI Power Management and the related functions.)
115
Linus Torvalds1da177e2005-04-16 15:20:36 -0700116 enable_wake Enable device to generate wake events from a low power
117 state.
118
Grant Grundler74da15e2006-12-25 01:06:35 -0700119 shutdown Hook into reboot_notifier_list (kernel/sys.c).
120 Intended to stop any idling DMA operations.
121 Useful for enabling wake-on-lan (NIC) or changing
122 the power state of a device before reboot.
123 e.g. drivers/net/e100.c.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700124
Grant Grundler74da15e2006-12-25 01:06:35 -0700125 err_handler See Documentation/pci-error-recovery.txt
Linus Torvalds1da177e2005-04-16 15:20:36 -0700126
Grant Grundler74da15e2006-12-25 01:06:35 -0700127
128The ID table is an array of struct pci_device_id entries ending with an
129all-zero entry. Each entry consists of:
130
131 vendor,device Vendor and device ID to match (or PCI_ANY_ID)
132
Linus Torvalds1da177e2005-04-16 15:20:36 -0700133 subvendor, Subsystem vendor and device ID to match (or PCI_ANY_ID)
Grant Grundler74da15e2006-12-25 01:06:35 -0700134 subdevice,
135
136 class Device class, subclass, and "interface" to match.
137 See Appendix D of the PCI Local Bus Spec or
138 include/linux/pci_ids.h for a full list of classes.
139 Most drivers do not need to specify class/class_mask
140 as vendor/device is normally sufficient.
141
142 class_mask limit which sub-fields of the class field are compared.
143 See drivers/scsi/sym53c8xx_2/ for example of usage.
144
Linus Torvalds1da177e2005-04-16 15:20:36 -0700145 driver_data Data private to the driver.
Grant Grundler74da15e2006-12-25 01:06:35 -0700146 Most drivers don't need to use driver_data field.
147 Best practice is to use driver_data as an index
148 into a static list of equivalent device types,
149 instead of using it as a pointer.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700150
Linus Torvalds1da177e2005-04-16 15:20:36 -0700151
Grant Grundler74da15e2006-12-25 01:06:35 -0700152Most drivers only need PCI_DEVICE() or PCI_DEVICE_CLASS() to set up
153a pci_device_id table.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700154
Grant Grundler74da15e2006-12-25 01:06:35 -0700155New PCI IDs may be added to a device driver pci_ids table at runtime
156as shown below:
Linus Torvalds1da177e2005-04-16 15:20:36 -0700157
158echo "vendor device subvendor subdevice class class_mask driver_data" > \
Grant Grundler74da15e2006-12-25 01:06:35 -0700159/sys/bus/pci/drivers/{driver}/new_id
160
161All fields are passed in as hexadecimal values (no leading 0x).
Jean Delvare6ba18632007-04-07 17:21:28 +0200162The vendor and device fields are mandatory, the others are optional. Users
163need pass only as many optional fields as necessary:
164 o subvendor and subdevice fields default to PCI_ANY_ID (FFFFFFFF)
Grant Grundler74da15e2006-12-25 01:06:35 -0700165 o class and classmask fields default to 0
166 o driver_data defaults to 0UL.
167
168Once added, the driver probe routine will be invoked for any unclaimed
169PCI devices listed in its (newly updated) pci_ids list.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700170
171When the driver exits, it just calls pci_unregister_driver() and the PCI layer
172automatically calls the remove hook for all devices handled by the driver.
173
Grant Grundler74da15e2006-12-25 01:06:35 -0700174
1751.1 "Attributes" for driver functions/data
176
Linus Torvalds1da177e2005-04-16 15:20:36 -0700177Please mark the initialization and cleanup functions where appropriate
178(the corresponding macros are defined in <linux/init.h>):
179
180 __init Initialization code. Thrown away after the driver
181 initializes.
182 __exit Exit code. Ignored for non-modular drivers.
Grant Grundler74da15e2006-12-25 01:06:35 -0700183
184
185 __devinit Device initialization code.
186 Identical to __init if the kernel is not compiled
187 with CONFIG_HOTPLUG, normal function otherwise.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700188 __devexit The same for __exit.
189
Grant Grundler74da15e2006-12-25 01:06:35 -0700190Tips on when/where to use the above attributes:
191 o The module_init()/module_exit() functions (and all
192 initialization functions called _only_ from these)
193 should be marked __init/__exit.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700194
Grant Grundler74da15e2006-12-25 01:06:35 -0700195 o Do not mark the struct pci_driver.
196
197 o The ID table array should be marked __devinitdata.
198
199 o The probe() and remove() functions should be marked __devinit
200 and __devexit respectively. All initialization functions
201 exclusively called by the probe() routine, can be marked __devinit.
202 Ditto for remove() and __devexit.
203
Grant Grundler26ba05e2007-02-11 00:04:04 -0700204 o If mydriver_remove() is marked with __devexit(), then all address
205 references to mydriver_remove must use __devexit_p(mydriver_remove)
Grant Grundler74da15e2006-12-25 01:06:35 -0700206 (in the struct pci_driver declaration for example).
207 __devexit_p() will generate the function name _or_ NULL if the
208 function will be discarded. For an example, see drivers/net/tg3.c.
209
210 o Do NOT mark a function if you are not sure which mark to use.
211 Better to not mark the function than mark the function wrong.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700212
213
Grant Grundler74da15e2006-12-25 01:06:35 -0700214
2152. How to find PCI devices manually
216~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
217
218PCI drivers should have a really good reason for not using the
219pci_register_driver() interface to search for PCI devices.
220The main reason PCI devices are controlled by multiple drivers
221is because one PCI device implements several different HW services.
222E.g. combined serial/parallel port/floppy controller.
223
224A manual search may be performed using the following constructs:
Linus Torvalds1da177e2005-04-16 15:20:36 -0700225
226Searching by vendor and device ID:
227
228 struct pci_dev *dev = NULL;
229 while (dev = pci_get_device(VENDOR_ID, DEVICE_ID, dev))
230 configure_device(dev);
231
232Searching by class ID (iterate in a similar way):
233
234 pci_get_class(CLASS_ID, dev)
235
236Searching by both vendor/device and subsystem vendor/device ID:
237
Grant Grundler74da15e2006-12-25 01:06:35 -0700238 pci_get_subsys(VENDOR_ID,DEVICE_ID, SUBSYS_VENDOR_ID, SUBSYS_DEVICE_ID, dev).
Linus Torvalds1da177e2005-04-16 15:20:36 -0700239
Grant Grundler74da15e2006-12-25 01:06:35 -0700240You can use the constant PCI_ANY_ID as a wildcard replacement for
Linus Torvalds1da177e2005-04-16 15:20:36 -0700241VENDOR_ID or DEVICE_ID. This allows searching for any device from a
242specific vendor, for example.
243
Grant Grundler74da15e2006-12-25 01:06:35 -0700244These functions are hotplug-safe. They increment the reference count on
Linus Torvalds1da177e2005-04-16 15:20:36 -0700245the pci_dev that they return. You must eventually (possibly at module unload)
246decrement the reference count on these devices by calling pci_dev_put().
247
248
Linus Torvalds1da177e2005-04-16 15:20:36 -0700249
Grant Grundler74da15e2006-12-25 01:06:35 -07002503. Device Initialization Steps
251~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Linus Torvalds1da177e2005-04-16 15:20:36 -0700252
Grant Grundler74da15e2006-12-25 01:06:35 -0700253As noted in the introduction, most PCI drivers need the following steps
254for device initialization:
255
256 Enable the device
257 Request MMIO/IOP resources
258 Set the DMA mask size (for both coherent and streaming DMA)
259 Allocate and initialize shared control data (pci_allocate_coherent())
260 Access device configuration space (if needed)
261 Register IRQ handler (request_irq())
262 Initialize non-PCI (i.e. LAN/SCSI/etc parts of the chip)
263 Enable DMA/processing engines.
264
265The driver can access PCI config space registers at any time.
266(Well, almost. When running BIST, config space can go away...but
267that will just result in a PCI Bus Master Abort and config reads
268will return garbage).
269
270
2713.1 Enable the PCI device
272~~~~~~~~~~~~~~~~~~~~~~~~~
273Before touching any device registers, the driver needs to enable
274the PCI device by calling pci_enable_device(). This will:
275 o wake up the device if it was in suspended state,
276 o allocate I/O and memory regions of the device (if BIOS did not),
277 o allocate an IRQ (if BIOS did not).
278
279NOTE: pci_enable_device() can fail! Check the return value.
280NOTE2: Also see pci_enable_device_bars() below. Drivers can
281 attempt to enable only a subset of BARs they need.
282
283[ OS BUG: we don't check resource allocations before enabling those
284 resources. The sequence would make more sense if we called
285 pci_request_resources() before calling pci_enable_device().
286 Currently, the device drivers can't detect the bug when when two
287 devices have been allocated the same range. This is not a common
288 problem and unlikely to get fixed soon.
289
290 This has been discussed before but not changed as of 2.6.19:
291 http://lkml.org/lkml/2006/3/2/194
292]
293
294pci_set_master() will enable DMA by setting the bus master bit
295in the PCI_COMMAND register. It also fixes the latency timer value if
296it's set to something bogus by the BIOS.
297
298If the PCI device can use the PCI Memory-Write-Invalidate transaction,
Linus Torvalds1da177e2005-04-16 15:20:36 -0700299call pci_set_mwi(). This enables the PCI_COMMAND bit for Mem-Wr-Inval
300and also ensures that the cache line size register is set correctly.
Grant Grundler74da15e2006-12-25 01:06:35 -0700301Check the return value of pci_set_mwi() as not all architectures
302or chip-sets may support Memory-Write-Invalidate.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700303
Grant Grundler74da15e2006-12-25 01:06:35 -0700304
3053.2 Request MMIO/IOP resources
306~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
307Memory (MMIO), and I/O port addresses should NOT be read directly
308from the PCI device config space. Use the values in the pci_dev structure
309as the PCI "bus address" might have been remapped to a "host physical"
310address by the arch/chip-set specific kernel support.
311
312See Documentation/IO-mapping.txt for how to access device registers
313or device memory.
314
315The device driver needs to call pci_request_region() to verify
316no other device is already using the same address resource.
317Conversely, drivers should call pci_release_region() AFTER
Linus Torvalds1da177e2005-04-16 15:20:36 -0700318calling pci_disable_device().
Grant Grundler74da15e2006-12-25 01:06:35 -0700319The idea is to prevent two devices colliding on the same address range.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700320
Grant Grundler74da15e2006-12-25 01:06:35 -0700321[ See OS BUG comment above. Currently (2.6.19), The driver can only
322 determine MMIO and IO Port resource availability _after_ calling
323 pci_enable_device(). ]
324
325Generic flavors of pci_request_region() are request_mem_region()
326(for MMIO ranges) and request_region() (for IO Port ranges).
327Use these for address resources that are not described by "normal" PCI
328BARs.
329
330Also see pci_request_selected_regions() below.
331
332
3333.3 Set the DMA mask size
334~~~~~~~~~~~~~~~~~~~~~~~~~
335[ If anything below doesn't make sense, please refer to
336 Documentation/DMA-API.txt. This section is just a reminder that
337 drivers need to indicate DMA capabilities of the device and is not
338 an authoritative source for DMA interfaces. ]
339
340While all drivers should explicitly indicate the DMA capability
341(e.g. 32 or 64 bit) of the PCI bus master, devices with more than
34232-bit bus master capability for streaming data need the driver
343to "register" this capability by calling pci_set_dma_mask() with
344appropriate parameters. In general this allows more efficient DMA
345on systems where System RAM exists above 4G _physical_ address.
346
347Drivers for all PCI-X and PCIe compliant devices must call
348pci_set_dma_mask() as they are 64-bit DMA devices.
349
350Similarly, drivers must also "register" this capability if the device
351can directly address "consistent memory" in System RAM above 4G physical
352address by calling pci_set_consistent_dma_mask().
353Again, this includes drivers for all PCI-X and PCIe compliant devices.
354Many 64-bit "PCI" devices (before PCI-X) and some PCI-X devices are
35564-bit DMA capable for payload ("streaming") data but not control
356("consistent") data.
357
358
3593.4 Setup shared control data
360~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
361Once the DMA masks are set, the driver can allocate "consistent" (a.k.a. shared)
362memory. See Documentation/DMA-API.txt for a full description of
363the DMA APIs. This section is just a reminder that it needs to be done
364before enabling DMA on the device.
365
366
3673.5 Initialize device registers
368~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
369Some drivers will need specific "capability" fields programmed
370or other "vendor specific" register initialized or reset.
371E.g. clearing pending interrupts.
372
373
3743.6 Register IRQ handler
375~~~~~~~~~~~~~~~~~~~~~~~~
Michael Opdenacker59c51592007-05-09 08:57:56 +0200376While calling request_irq() is the last step described here,
Grant Grundler74da15e2006-12-25 01:06:35 -0700377this is often just another intermediate step to initialize a device.
378This step can often be deferred until the device is opened for use.
379
380All interrupt handlers for IRQ lines should be registered with IRQF_SHARED
381and use the devid to map IRQs to devices (remember that all PCI IRQ lines
382can be shared).
383
384request_irq() will associate an interrupt handler and device handle
385with an interrupt number. Historically interrupt numbers represent
386IRQ lines which run from the PCI device to the Interrupt controller.
387With MSI and MSI-X (more below) the interrupt number is a CPU "vector".
388
389request_irq() also enables the interrupt. Make sure the device is
390quiesced and does not have any interrupts pending before registering
391the interrupt handler.
392
393MSI and MSI-X are PCI capabilities. Both are "Message Signaled Interrupts"
394which deliver interrupts to the CPU via a DMA write to a Local APIC.
395The fundamental difference between MSI and MSI-X is how multiple
396"vectors" get allocated. MSI requires contiguous blocks of vectors
397while MSI-X can allocate several individual ones.
398
399MSI capability can be enabled by calling pci_enable_msi() or
400pci_enable_msix() before calling request_irq(). This causes
401the PCI support to program CPU vector data into the PCI device
402capability registers.
403
404If your PCI device supports both, try to enable MSI-X first.
405Only one can be enabled at a time. Many architectures, chip-sets,
406or BIOSes do NOT support MSI or MSI-X and the call to pci_enable_msi/msix
407will fail. This is important to note since many drivers have
408two (or more) interrupt handlers: one for MSI/MSI-X and another for IRQs.
409They choose which handler to register with request_irq() based on the
410return value from pci_enable_msi/msix().
411
412There are (at least) two really good reasons for using MSI:
4131) MSI is an exclusive interrupt vector by definition.
414 This means the interrupt handler doesn't have to verify
415 its device caused the interrupt.
416
4172) MSI avoids DMA/IRQ race conditions. DMA to host memory is guaranteed
418 to be visible to the host CPU(s) when the MSI is delivered. This
419 is important for both data coherency and avoiding stale control data.
420 This guarantee allows the driver to omit MMIO reads to flush
421 the DMA stream.
422
423See drivers/infiniband/hw/mthca/ or drivers/net/tg3.c for examples
424of MSI/MSI-X usage.
425
426
427
4284. PCI device shutdown
429~~~~~~~~~~~~~~~~~~~~~~~
430
431When a PCI device driver is being unloaded, most of the following
432steps need to be performed:
433
434 Disable the device from generating IRQs
435 Release the IRQ (free_irq())
436 Stop all DMA activity
437 Release DMA buffers (both streaming and consistent)
438 Unregister from other subsystems (e.g. scsi or netdev)
439 Disable device from responding to MMIO/IO Port addresses
440 Release MMIO/IO Port resource(s)
441
442
4434.1 Stop IRQs on the device
444~~~~~~~~~~~~~~~~~~~~~~~~~~~
445How to do this is chip/device specific. If it's not done, it opens
446the possibility of a "screaming interrupt" if (and only if)
447the IRQ is shared with another device.
448
449When the shared IRQ handler is "unhooked", the remaining devices
450using the same IRQ line will still need the IRQ enabled. Thus if the
451"unhooked" device asserts IRQ line, the system will respond assuming
452it was one of the remaining devices asserted the IRQ line. Since none
453of the other devices will handle the IRQ, the system will "hang" until
454it decides the IRQ isn't going to get handled and masks the IRQ (100,000
455iterations later). Once the shared IRQ is masked, the remaining devices
456will stop functioning properly. Not a nice situation.
457
458This is another reason to use MSI or MSI-X if it's available.
459MSI and MSI-X are defined to be exclusive interrupts and thus
460are not susceptible to the "screaming interrupt" problem.
461
462
4634.2 Release the IRQ
464~~~~~~~~~~~~~~~~~~~
465Once the device is quiesced (no more IRQs), one can call free_irq().
466This function will return control once any pending IRQs are handled,
467"unhook" the drivers IRQ handler from that IRQ, and finally release
468the IRQ if no one else is using it.
469
470
4714.3 Stop all DMA activity
472~~~~~~~~~~~~~~~~~~~~~~~~~
473It's extremely important to stop all DMA operations BEFORE attempting
474to deallocate DMA control data. Failure to do so can result in memory
475corruption, hangs, and on some chip-sets a hard crash.
476
477Stopping DMA after stopping the IRQs can avoid races where the
478IRQ handler might restart DMA engines.
479
480While this step sounds obvious and trivial, several "mature" drivers
481didn't get this step right in the past.
482
483
4844.4 Release DMA buffers
485~~~~~~~~~~~~~~~~~~~~~~~
486Once DMA is stopped, clean up streaming DMA first.
487I.e. unmap data buffers and return buffers to "upstream"
488owners if there is one.
489
490Then clean up "consistent" buffers which contain the control data.
491
492See Documentation/DMA-API.txt for details on unmapping interfaces.
493
494
4954.5 Unregister from other subsystems
496~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
497Most low level PCI device drivers support some other subsystem
498like USB, ALSA, SCSI, NetDev, Infiniband, etc. Make sure your
499driver isn't losing resources from that other subsystem.
500If this happens, typically the symptom is an Oops (panic) when
501the subsystem attempts to call into a driver that has been unloaded.
502
503
5044.6 Disable Device from responding to MMIO/IO Port addresses
505~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
506io_unmap() MMIO or IO Port resources and then call pci_disable_device().
507This is the symmetric opposite of pci_enable_device().
508Do not access device registers after calling pci_disable_device().
509
510
5114.7 Release MMIO/IO Port Resource(s)
512~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
513Call pci_release_region() to mark the MMIO or IO Port range as available.
514Failure to do so usually results in the inability to reload the driver.
515
516
517
5185. How to access PCI config space
Linus Torvalds1da177e2005-04-16 15:20:36 -0700519~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Grant Grundler74da15e2006-12-25 01:06:35 -0700520
521You can use pci_(read|write)_config_(byte|word|dword) to access the config
Linus Torvalds1da177e2005-04-16 15:20:36 -0700522space of a device represented by struct pci_dev *. All these functions return 0
523when successful or an error code (PCIBIOS_...) which can be translated to a text
524string by pcibios_strerror. Most drivers expect that accesses to valid PCI
525devices don't fail.
526
Grant Grundler74da15e2006-12-25 01:06:35 -0700527If you don't have a struct pci_dev available, you can call
Linus Torvalds1da177e2005-04-16 15:20:36 -0700528pci_bus_(read|write)_config_(byte|word|dword) to access a given device
529and function on that bus.
530
Grant Grundler74da15e2006-12-25 01:06:35 -0700531If you access fields in the standard portion of the config header, please
Linus Torvalds1da177e2005-04-16 15:20:36 -0700532use symbolic names of locations and bits declared in <linux/pci.h>.
533
Grant Grundler74da15e2006-12-25 01:06:35 -0700534If you need to access Extended PCI Capability registers, just call
Linus Torvalds1da177e2005-04-16 15:20:36 -0700535pci_find_capability() for the particular capability and it will find the
536corresponding register block for you.
537
538
Linus Torvalds1da177e2005-04-16 15:20:36 -0700539
5406. Other interesting functions
541~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Grant Grundler74da15e2006-12-25 01:06:35 -0700542
Linus Torvalds1da177e2005-04-16 15:20:36 -0700543pci_find_slot() Find pci_dev corresponding to given bus and
544 slot numbers.
545pci_set_power_state() Set PCI Power Management state (0=D0 ... 3=D3)
546pci_find_capability() Find specified capability in device's capability
547 list.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700548pci_resource_start() Returns bus start address for a given PCI region
549pci_resource_end() Returns bus end address for a given PCI region
550pci_resource_len() Returns the byte length of a PCI region
551pci_set_drvdata() Set private driver data pointer for a pci_dev
552pci_get_drvdata() Return private driver data pointer for a pci_dev
553pci_set_mwi() Enable Memory-Write-Invalidate transactions.
554pci_clear_mwi() Disable Memory-Write-Invalidate transactions.
555
556
Grant Grundler74da15e2006-12-25 01:06:35 -0700557
Linus Torvalds1da177e2005-04-16 15:20:36 -07005587. Miscellaneous hints
559~~~~~~~~~~~~~~~~~~~~~~
Grant Grundler74da15e2006-12-25 01:06:35 -0700560
561When displaying PCI device names to the user (for example when a driver wants
562to tell the user what card has it found), please use pci_name(pci_dev).
Linus Torvalds1da177e2005-04-16 15:20:36 -0700563
564Always refer to the PCI devices by a pointer to the pci_dev structure.
565All PCI layer functions use this identification and it's the only
566reasonable one. Don't use bus/slot/function numbers except for very
567special purposes -- on systems with multiple primary buses their semantics
568can be pretty complex.
569
Linus Torvalds1da177e2005-04-16 15:20:36 -0700570Don't try to turn on Fast Back to Back writes in your driver. All devices
571on the bus need to be capable of doing it, so this is something which needs
572to be handled by platform and generic code, not individual drivers.
573
574
Grant Grundler74da15e2006-12-25 01:06:35 -0700575
Ingo Oeser9b860b82006-04-18 11:20:55 +02005768. Vendor and device identifications
577~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Ingo Oeser9b860b82006-04-18 11:20:55 +0200578
Grant Grundler74da15e2006-12-25 01:06:35 -0700579One is not not required to add new device ids to include/linux/pci_ids.h.
580Please add PCI_VENDOR_ID_xxx for vendors and a hex constant for device ids.
Ingo Oeser9b860b82006-04-18 11:20:55 +0200581
Grant Grundler74da15e2006-12-25 01:06:35 -0700582PCI_VENDOR_ID_xxx constants are re-used. The device ids are arbitrary
583hex numbers (vendor controlled) and normally used only in a single
584location, the pci_device_id table.
585
586Please DO submit new vendor/device ids to pciids.sourceforge.net project.
587
588
Ingo Oeser9b860b82006-04-18 11:20:55 +0200589
5909. Obsolete functions
Linus Torvalds1da177e2005-04-16 15:20:36 -0700591~~~~~~~~~~~~~~~~~~~~~
Grant Grundler74da15e2006-12-25 01:06:35 -0700592
Linus Torvalds1da177e2005-04-16 15:20:36 -0700593There are several functions which you might come across when trying to
594port an old driver to the new PCI interface. They are no longer present
595in the kernel as they aren't compatible with hotplug or PCI domains or
596having sane locking.
597
Grant Grundler74da15e2006-12-25 01:06:35 -0700598pci_find_device() Superseded by pci_get_device()
599pci_find_subsys() Superseded by pci_get_subsys()
600pci_find_slot() Superseded by pci_get_slot()
601
602
603The alternative is the traditional PCI device driver that walks PCI
604device lists. This is still possible but discouraged.
605
606
607
60810. pci_enable_device_bars() and Legacy I/O Port space
609~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
610
611Large servers may not be able to provide I/O port resources to all PCI
612devices. I/O Port space is only 64KB on Intel Architecture[1] and is
613likely also fragmented since the I/O base register of PCI-to-PCI
614bridge will usually be aligned to a 4KB boundary[2]. On such systems,
615pci_enable_device() and pci_request_region() will fail when
616attempting to enable I/O Port regions that don't have I/O Port
617resources assigned.
618
619Fortunately, many PCI devices which request I/O Port resources also
620provide access to the same registers via MMIO BARs. These devices can
621be handled without using I/O port space and the drivers typically
622offer a CONFIG_ option to only use MMIO regions
623(e.g. CONFIG_TULIP_MMIO). PCI devices typically provide I/O port
624interface for legacy OSes and will work when I/O port resources are not
625assigned. The "PCI Local Bus Specification Revision 3.0" discusses
626this on p.44, "IMPLEMENTATION NOTE".
627
628If your PCI device driver doesn't need I/O port resources assigned to
629I/O Port BARs, you should use pci_enable_device_bars() instead of
630pci_enable_device() in order not to enable I/O port regions for the
631corresponding devices. In addition, you should use
632pci_request_selected_regions() and pci_release_selected_regions()
633instead of pci_request_regions()/pci_release_regions() in order not to
634request/release I/O port regions for the corresponding devices.
635
636[1] Some systems support 64KB I/O port space per PCI segment.
637[2] Some PCI-to-PCI bridges support optional 1KB aligned I/O base.
638
639
640
64111. MMIO Space and "Write Posting"
642~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
643
644Converting a driver from using I/O Port space to using MMIO space
645often requires some additional changes. Specifically, "write posting"
646needs to be handled. Many drivers (e.g. tg3, acenic, sym53c8xx_2)
647already do this. I/O Port space guarantees write transactions reach the PCI
648device before the CPU can continue. Writes to MMIO space allow the CPU
649to continue before the transaction reaches the PCI device. HW weenies
650call this "Write Posting" because the write completion is "posted" to
651the CPU before the transaction has reached its destination.
652
653Thus, timing sensitive code should add readl() where the CPU is
654expected to wait before doing other work. The classic "bit banging"
655sequence works fine for I/O Port space:
656
657 for (i = 8; --i; val >>= 1) {
658 outb(val & 1, ioport_reg); /* write bit */
659 udelay(10);
660 }
661
662The same sequence for MMIO space should be:
663
664 for (i = 8; --i; val >>= 1) {
665 writeb(val & 1, mmio_reg); /* write bit */
666 readb(safe_mmio_reg); /* flush posted write */
667 udelay(10);
668 }
669
670It is important that "safe_mmio_reg" not have any side effects that
671interferes with the correct operation of the device.
672
673Another case to watch out for is when resetting a PCI device. Use PCI
674Configuration space reads to flush the writel(). This will gracefully
675handle the PCI master abort on all platforms if the PCI device is
676expected to not respond to a readl(). Most x86 platforms will allow
677MMIO reads to master abort (a.k.a. "Soft Fail") and return garbage
678(e.g. ~0). But many RISC platforms will crash (a.k.a."Hard Fail").
679