diff options
Diffstat (limited to 'Documentation/filesystems/sysfs-pci.txt')
| -rw-r--r-- | Documentation/filesystems/sysfs-pci.txt | 50 |
1 files changed, 42 insertions, 8 deletions
diff --git a/Documentation/filesystems/sysfs-pci.txt b/Documentation/filesystems/sysfs-pci.txt index 988a62fae11..74eaac26f8b 100644 --- a/Documentation/filesystems/sysfs-pci.txt +++ b/Documentation/filesystems/sysfs-pci.txt @@ -1,4 +1,5 @@ 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: @@ -8,8 +9,10 @@ that support it. For example, a given bus might look like this: | |-- class | |-- config | |-- device + | |-- enable | |-- irq | |-- local_cpus + | |-- remove | |-- resource | |-- resource0 | |-- resource1 @@ -31,10 +34,13 @@ files, each with their own function. class PCI class (ascii, ro) config PCI config space (binary, rw) device PCI device (ascii, ro) + enable Whether the device is enabled (ascii, rw) irq IRQ number (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) + resource0..N PCI resource N, if present (binary, mmap, rw[1]) + resource0_wc..N_wc PCI WC map resource N, if prefetchable (binary, mmap) rom PCI ROM resource, if present (binary, ro) subsystem_device PCI subsystem device (ascii, ro) subsystem_vendor PCI subsystem vendor (ascii, ro) @@ -42,22 +48,49 @@ files, each with their own function. ro - read only file rw - file is readable and writable + wo - write only file 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. -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. +[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 +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 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 +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. + +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. Note +that the device must be enabled for a rom read to return data successfully. +In the event a driver is not bound to the device, it can be enabled using the +'enable' file, documented above. + +The 'remove' file is used to remove the PCI device, by writing a non-zero +integer to the file. This does not involve any kind of hot-plug functionality, +e.g. powering off the device. The device is removed from the kernel's list of +PCI devices, the sysfs directory for it is removed, and the device will be +removed from any drivers attached to it. Removal of PCI root buses is +disallowed. 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, +underlying platform supports them. They're located in the PCI class hierarchy, e.g. /sys/class/pci_bus/0000:17/ @@ -75,6 +108,7 @@ 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. |