Based on kernel version 2.6.26. Page generated on 2008-07-16 21:12 EST.
1 Accessing PCI device resources through sysfs 2 -------------------------------------------- 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 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 22 `-- ... 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) 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 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. 63 64 Accessing legacy resources through sysfs 65 ---------------------------------------- 66 67 Legacy I/O port and ISA memory resources are also provided in sysfs if the 68 underlying platform supports them. They're located in the PCI class hierarchy, 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 86 -------------------------------------- 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 95 pci_legacy_read, pci_legacy_write and pci_mmap_legacy_page_range functions.