1 How To Write Linux PCI Drivers
3 by Martin Mares <mj@ucw.cz> on 07-Feb-2000
5 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
6 The world of PCI is vast and it's full of (mostly unpleasant) surprises.
7 Different PCI devices have different requirements and different bugs --
8 because of this, the PCI support layer in Linux kernel is not as trivial
9 as one would wish. This short pamphlet tries to help all potential driver
10 authors to find their way through the deep forests of PCI handling.
13 0. Structure of PCI drivers
14 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
15 There exist two kinds of PCI drivers: new-style ones (which leave most of
16 probing for devices to the PCI layer and support online insertion and removal
17 of devices [thus supporting PCI, hot-pluggable PCI and CardBus in single
18 driver]) and old-style ones which just do all the probing themselves. Unless
19 you have a very good reason to do so, please don't use the old way of probing
20 in any new code. After the driver finds the devices it wishes to operate
21 on (either the old or the new way), it needs to perform the following steps:
24 Access device configuration space
25 Discover resources (addresses and IRQ numbers) provided by the device
26 Allocate these resources
27 Communicate with the device
29 Most of these topics are covered by the following sections, for the rest
30 look at <linux/pci.h>, it's hopefully well commented.
32 If the PCI subsystem is not configured (CONFIG_PCI is not set), most of
33 the functions described below are defined as inline functions either completely
34 empty or just returning an appropriate error codes to avoid lots of ifdefs
40 The new-style drivers just call pci_register_driver during their initialization
41 with a pointer to a structure describing the driver (struct pci_driver) which
44 name Name of the driver
45 id_table Pointer to table of device ID's the driver is
46 interested in. Most drivers should export this
47 table using MODULE_DEVICE_TABLE(pci,...).
48 Set to NULL to call probe() function for every
49 PCI device known to the system.
50 probe Pointer to a probing function which gets called (during
51 execution of pci_register_driver for already existing
52 devices or later if a new device gets inserted) for all
53 PCI devices which match the ID table and are not handled
54 by the other drivers yet. This function gets passed a
55 pointer to the pci_dev structure representing the device
56 and also which entry in the ID table did the device
57 match. It returns zero when the driver has accepted the
58 device or an error code (negative number) otherwise.
59 This function always gets called from process context,
61 remove Pointer to a function which gets called whenever a
62 device being handled by this driver is removed (either
63 during deregistration of the driver or when it's
64 manually pulled out of a hot-pluggable slot). This
65 function always gets called from process context, so it
67 save_state Save a device's state before it's suspend.
68 suspend Put device into low power state.
69 resume Wake device from low power state.
70 enable_wake Enable device to generate wake events from a low power
73 (Please see Documentation/power/pci.txt for descriptions
74 of PCI Power Management and the related functions)
76 The ID table is an array of struct pci_device_id ending with a all-zero entry.
77 Each entry consists of:
79 vendor, device Vendor and device ID to match (or PCI_ANY_ID)
80 subvendor, Subsystem vendor and device ID to match (or PCI_ANY_ID)
82 class, Device class to match. The class_mask tells which bits
83 class_mask of the class are honored during the comparison.
84 driver_data Data private to the driver.
86 When the driver exits, it just calls pci_unregister_driver() and the PCI layer
87 automatically calls the remove hook for all devices handled by the driver.
89 Please mark the initialization and cleanup functions where appropriate
90 (the corresponding macros are defined in <linux/init.h>):
92 __init Initialization code. Thrown away after the driver
94 __exit Exit code. Ignored for non-modular drivers.
95 __devinit Device initialization code. Identical to __init if
96 the kernel is not compiled with CONFIG_HOTPLUG, normal
98 __devexit The same for __exit.
101 The module_init()/module_exit() functions (and all initialization
102 functions called only from these) should be marked __init/exit.
103 The struct pci_driver shouldn't be marked with any of these tags.
104 The ID table array should be marked __devinitdata.
105 The probe() and remove() functions (and all initialization
106 functions called only from these) should be marked __devinit/exit.
107 If you are sure the driver is not a hotplug driver then use only
108 __init/exit __initdata/exitdata.
110 Pointers to functions marked as __devexit must be created using
111 __devexit_p(function_name). That will generate the function
112 name or NULL if the __devexit function will be discarded.
115 2. How to find PCI devices manually (the old style)
116 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
117 PCI drivers not using the pci_register_driver() interface search
118 for PCI devices manually using the following constructs:
120 Searching by vendor and device ID:
122 struct pci_dev *dev = NULL;
123 while (dev = pci_find_device(VENDOR_ID, DEVICE_ID, dev))
124 configure_device(dev);
126 Searching by class ID (iterate in a similar way):
128 pci_find_class(CLASS_ID, dev)
130 Searching by both vendor/device and subsystem vendor/device ID:
132 pci_find_subsys(VENDOR_ID, DEVICE_ID, SUBSYS_VENDOR_ID, SUBSYS_DEVICE_ID, dev).
134 You can use the constant PCI_ANY_ID as a wildcard replacement for
135 VENDOR_ID or DEVICE_ID. This allows searching for any device from a
136 specific vendor, for example.
138 In case you need to decide according to some more complex criteria,
139 you can walk the list of all known PCI devices yourself:
142 pci_for_each_dev(dev) {
143 ... do anything you want with dev ...
146 For compatibility with device ordering in older kernels, you can also
147 use pci_for_each_dev_reverse(dev) for walking the list in the opposite
153 Before you do anything with the device you've found, you need to enable
154 it by calling pci_enable_device() which enables I/O and memory regions of
155 the device, assigns missing resources if needed and wakes up the device
156 if it was in suspended state. Please note that this function can fail.
158 If you want to use the device in bus mastering mode, call pci_set_master()
159 which enables the bus master bit in PCI_COMMAND register and also fixes
160 the latency timer value if it's set to something bogus by the BIOS.
162 If you want to use the PCI Memory-Write-Invalidate transaction,
163 call pci_set_mwi(). This enables bit PCI_COMMAND bit for Mem-Wr-Inval
164 and also ensures that the cache line size register is set correctly.
165 Make sure to check the return value of pci_set_mwi(), not all architectures
166 may support Memory-Write-Invalidate.
168 4. How to access PCI config space
169 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
170 You can use pci_(read|write)_config_(byte|word|dword) to access the config
171 space of a device represented by struct pci_dev *. All these functions return 0
172 when successful or an error code (PCIBIOS_...) which can be translated to a text
173 string by pcibios_strerror. Most drivers expect that accesses to valid PCI
176 If you access fields in the standard portion of the config header, please
177 use symbolic names of locations and bits declared in <linux/pci.h>.
179 If you need to access Extended PCI Capability registers, just call
180 pci_find_capability() for the particular capability and it will find the
181 corresponding register block for you.
184 5. Addresses and interrupts
185 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
186 Memory and port addresses and interrupt numbers should NOT be read from the
187 config space. You should use the values in the pci_dev structure as they might
188 have been remapped by the kernel.
190 See Documentation/IO-mapping.txt for how to access device memory.
192 You still need to call request_region() for I/O regions and
193 request_mem_region() for memory regions to make sure nobody else is using the
196 All interrupt handlers should be registered with SA_SHIRQ and use the devid
197 to map IRQs to devices (remember that all PCI interrupts are shared).
200 6. Other interesting functions
201 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
202 pci_find_slot() Find pci_dev corresponding to given bus and
204 pci_set_power_state() Set PCI Power Management state (0=D0 ... 3=D3)
205 pci_find_capability() Find specified capability in device's capability
207 pci_module_init() Inline helper function for ensuring correct
208 pci_driver initialization and error handling.
209 pci_resource_start() Returns bus start address for a given PCI region
210 pci_resource_end() Returns bus end address for a given PCI region
211 pci_resource_len() Returns the byte length of a PCI region
212 pci_set_drvdata() Set private driver data pointer for a pci_dev
213 pci_get_drvdata() Return private driver data pointer for a pci_dev
214 pci_set_mwi() Enable Memory-Write-Invalidate transactions.
215 pci_clear_mwi() Disable Memory-Write-Invalidate transactions.
218 7. Miscellaneous hints
219 ~~~~~~~~~~~~~~~~~~~~~~
220 When displaying PCI slot names to the user (for example when a driver wants
221 to tell the user what card has it found), please use pci_dev->slot_name
224 Always refer to the PCI devices by a pointer to the pci_dev structure.
225 All PCI layer functions use this identification and it's the only
226 reasonable one. Don't use bus/slot/function numbers except for very
227 special purposes -- on systems with multiple primary buses their semantics
228 can be pretty complex.
230 If you're going to use PCI bus mastering DMA, take a look at
231 Documentation/DMA-mapping.txt.
234 8. Obsolete functions
235 ~~~~~~~~~~~~~~~~~~~~~
236 There are several functions kept only for compatibility with old drivers
237 not updated to the new PCI interface. Please don't use them in new code.
239 pcibios_present() Since ages, you don't need to test presence
240 of PCI subsystem when trying to talk with it.
241 If it's not there, the list of PCI devices
242 is empty and all functions for searching for
243 devices just return NULL.
244 pcibios_(read|write)_* Superseded by their pci_(read|write)_*
246 pcibios_find_* Superseded by their pci_find_* counterparts.