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Commit | Line | Data |
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1da177e4 | 1 | Accessing PCI device resources through sysfs |
5d135dff | 2 | -------------------------------------------- |
1da177e4 LT |
3 | |
4 | sysfs, usually mounted at /sys, provides access to PCI resources on platforms | |
5 | that support it. For example, a given bus might look like this: | |
6 | ||
7 | /sys/devices/pci0000:17 | |
8 | |-- 0000:17:00.0 | |
9 | | |-- class | |
10 | | |-- config | |
1da177e4 LT |
11 | | |-- device |
12 | | |-- irq | |
13 | | |-- local_cpus | |
14 | | |-- resource | |
15 | | |-- resource0 | |
16 | | |-- resource1 | |
17 | | |-- resource2 | |
18 | | |-- rom | |
19 | | |-- subsystem_device | |
20 | | |-- subsystem_vendor | |
21 | | `-- vendor | |
0b405a0f | 22 | `-- ... |
1da177e4 LT |
23 | |
24 | The topmost element describes the PCI domain and bus number. In this case, | |
25 | the domain number is 0000 and the bus number is 17 (both values are in hex). | |
26 | This bus contains a single function device in slot 0. The domain and bus | |
27 | numbers are reproduced for convenience. Under the device directory are several | |
28 | files, each with their own function. | |
29 | ||
30 | file function | |
31 | ---- -------- | |
32 | class PCI class (ascii, ro) | |
33 | config PCI config space (binary, rw) | |
1da177e4 LT |
34 | device PCI device (ascii, ro) |
35 | irq IRQ number (ascii, ro) | |
36 | local_cpus nearby CPU mask (cpumask, ro) | |
37 | resource PCI resource host addresses (ascii, ro) | |
38 | resource0..N PCI resource N, if present (binary, mmap) | |
39 | rom PCI ROM resource, if present (binary, ro) | |
40 | subsystem_device PCI subsystem device (ascii, ro) | |
41 | subsystem_vendor PCI subsystem vendor (ascii, ro) | |
42 | vendor PCI vendor (ascii, ro) | |
43 | ||
44 | ro - read only file | |
45 | rw - file is readable and writable | |
46 | mmap - file is mmapable | |
47 | ascii - file contains ascii text | |
48 | binary - file contains binary data | |
49 | cpumask - file contains a cpumask type | |
50 | ||
5d135dff JB |
51 | The read only files are informational, writes to them will be ignored, with |
52 | the exception of the 'rom' file. Writable files can be used to perform | |
53 | actions on the device (e.g. changing config space, detaching a device). | |
54 | mmapable files are available via an mmap of the file at offset 0 and can be | |
55 | used to do actual device programming from userspace. Note that some platforms | |
56 | don't support mmapping of certain resources, so be sure to check the return | |
57 | value from any attempted mmap. | |
58 | ||
59 | The 'rom' file is special in that it provides read-only access to the device's | |
60 | ROM file, if available. It's disabled by default, however, so applications | |
61 | should write the string "1" to the file to enable it before attempting a read | |
62 | call, and disable it following the access by writing "0" to the file. | |
1da177e4 LT |
63 | |
64 | Accessing legacy resources through sysfs | |
5d135dff | 65 | ---------------------------------------- |
1da177e4 LT |
66 | |
67 | Legacy I/O port and ISA memory resources are also provided in sysfs if the | |
1b3c3714 | 68 | underlying platform supports them. They're located in the PCI class hierarchy, |
1da177e4 LT |
69 | e.g. |
70 | ||
71 | /sys/class/pci_bus/0000:17/ | |
72 | |-- bridge -> ../../../devices/pci0000:17 | |
73 | |-- cpuaffinity | |
74 | |-- legacy_io | |
75 | `-- legacy_mem | |
76 | ||
77 | The legacy_io file is a read/write file that can be used by applications to | |
78 | do legacy port I/O. The application should open the file, seek to the desired | |
79 | port (e.g. 0x3e8) and do a read or a write of 1, 2 or 4 bytes. The legacy_mem | |
80 | file should be mmapped with an offset corresponding to the memory offset | |
81 | desired, e.g. 0xa0000 for the VGA frame buffer. The application can then | |
82 | simply dereference the returned pointer (after checking for errors of course) | |
83 | to access legacy memory space. | |
84 | ||
85 | Supporting PCI access on new platforms | |
5d135dff | 86 | -------------------------------------- |
1da177e4 LT |
87 | |
88 | In order to support PCI resource mapping as described above, Linux platform | |
89 | code must define HAVE_PCI_MMAP and provide a pci_mmap_page_range function. | |
90 | Platforms are free to only support subsets of the mmap functionality, but | |
91 | useful return codes should be provided. | |
92 | ||
93 | Legacy resources are protected by the HAVE_PCI_LEGACY define. Platforms | |
94 | wishing to support legacy functionality should define it and provide | |
0b405a0f | 95 | pci_legacy_read, pci_legacy_write and pci_mmap_legacy_page_range functions. |