96 lines
3.9 KiB
Plaintext
96 lines
3.9 KiB
Plaintext
Accessing PCI device resources through sysfs
|
|
--------------------------------------------
|
|
|
|
sysfs, usually mounted at /sys, provides access to PCI resources on platforms
|
|
that support it. For example, a given bus might look like this:
|
|
|
|
/sys/devices/pci0000:17
|
|
|-- 0000:17:00.0
|
|
| |-- class
|
|
| |-- config
|
|
| |-- device
|
|
| |-- irq
|
|
| |-- local_cpus
|
|
| |-- resource
|
|
| |-- resource0
|
|
| |-- resource1
|
|
| |-- resource2
|
|
| |-- rom
|
|
| |-- subsystem_device
|
|
| |-- subsystem_vendor
|
|
| `-- vendor
|
|
`-- ...
|
|
|
|
The topmost element describes the PCI domain and bus number. In this case,
|
|
the domain number is 0000 and the bus number is 17 (both values are in hex).
|
|
This bus contains a single function device in slot 0. The domain and bus
|
|
numbers are reproduced for convenience. Under the device directory are several
|
|
files, each with their own function.
|
|
|
|
file function
|
|
---- --------
|
|
class PCI class (ascii, ro)
|
|
config PCI config space (binary, rw)
|
|
device PCI device (ascii, ro)
|
|
irq IRQ number (ascii, ro)
|
|
local_cpus nearby CPU mask (cpumask, ro)
|
|
resource PCI resource host addresses (ascii, ro)
|
|
resource0..N PCI resource N, if present (binary, mmap)
|
|
rom PCI ROM resource, if present (binary, ro)
|
|
subsystem_device PCI subsystem device (ascii, ro)
|
|
subsystem_vendor PCI subsystem vendor (ascii, ro)
|
|
vendor PCI vendor (ascii, ro)
|
|
|
|
ro - read only file
|
|
rw - file is readable and writable
|
|
mmap - file is mmapable
|
|
ascii - file contains ascii text
|
|
binary - file contains binary data
|
|
cpumask - file contains a cpumask type
|
|
|
|
The read only files are informational, writes to them will be ignored, with
|
|
the exception of the 'rom' file. Writable files can be used to perform
|
|
actions on the device (e.g. changing config space, detaching a device).
|
|
mmapable files are available via an mmap of the file at offset 0 and can be
|
|
used to do actual device programming from userspace. Note that some platforms
|
|
don't support mmapping of certain resources, so be sure to check the return
|
|
value from any attempted mmap.
|
|
|
|
The 'rom' file is special in that it provides read-only access to the device's
|
|
ROM file, if available. It's disabled by default, however, so applications
|
|
should write the string "1" to the file to enable it before attempting a read
|
|
call, and disable it following the access by writing "0" to the file.
|
|
|
|
Accessing legacy resources through sysfs
|
|
----------------------------------------
|
|
|
|
Legacy I/O port and ISA memory resources are also provided in sysfs if the
|
|
underlying platform supports them. They're located in the PCI class heirarchy,
|
|
e.g.
|
|
|
|
/sys/class/pci_bus/0000:17/
|
|
|-- bridge -> ../../../devices/pci0000:17
|
|
|-- cpuaffinity
|
|
|-- legacy_io
|
|
`-- legacy_mem
|
|
|
|
The legacy_io file is a read/write file that can be used by applications to
|
|
do legacy port I/O. The application should open the file, seek to the desired
|
|
port (e.g. 0x3e8) and do a read or a write of 1, 2 or 4 bytes. The legacy_mem
|
|
file should be mmapped with an offset corresponding to the memory offset
|
|
desired, e.g. 0xa0000 for the VGA frame buffer. The application can then
|
|
simply dereference the returned pointer (after checking for errors of course)
|
|
to access legacy memory space.
|
|
|
|
Supporting PCI access on new platforms
|
|
--------------------------------------
|
|
|
|
In order to support PCI resource mapping as described above, Linux platform
|
|
code must define HAVE_PCI_MMAP and provide a pci_mmap_page_range function.
|
|
Platforms are free to only support subsets of the mmap functionality, but
|
|
useful return codes should be provided.
|
|
|
|
Legacy resources are protected by the HAVE_PCI_LEGACY define. Platforms
|
|
wishing to support legacy functionality should define it and provide
|
|
pci_legacy_read, pci_legacy_write and pci_mmap_legacy_page_range functions.
|