+.. SPDX-License-Identifier: GPL-2.0
+
+============================================
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:
+that support it. For example, a given bus might look like this::
/sys/devices/pci0000:17
|-- 0000:17:00.0
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)
local_cpus nearby CPU mask (cpumask, ro)
remove remove device from kernel's list (ascii, wo)
resource PCI resource host addresses (ascii, ro)
- resource0..N PCI resource N, if present (binary, mmap, rw[1])
+ resource0..N PCI resource N, if present (binary, mmap, rw\ [1]_)
resource0_wc..N_wc PCI WC map resource N, if prefetchable (binary, mmap)
revision PCI revision (ascii, ro)
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
binary - file contains binary data
cpumask - file contains a cpumask type
-[1] rw for RESOURCE_IO (I/O port) regions only
+.. [1] rw for RESOURCE_IO (I/O port) regions only
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
value from any attempted mmap. The most notable of these are I/O port
resources, which also provide read/write access.
-The 'enable' file provides a counter that indicates how many times the device
+The 'enable' file provides a counter that indicates how many times the device
has been enabled. If the 'enable' file currently returns '4', and a '1' is
echoed into it, it will then return '5'. Echoing a '0' into it will decrease
the count. Even when it returns to 0, though, some of the initialisation
-may not be reversed.
+may not be reversed.
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
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 hierarchy,
-e.g.
+e.g.::
/sys/class/pci_bus/0000:17/
|-- bridge -> ../../../devices/pci0000:17