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Diffstat (limited to 'Documentation/filesystems/sysfs-pci.txt')
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diff --git a/Documentation/filesystems/sysfs-pci.txt b/Documentation/filesystems/sysfs-pci.txt new file mode 100644 index 000000000000..e97d024eae77 --- /dev/null +++ b/Documentation/filesystems/sysfs-pci.txt @@ -0,0 +1,88 @@ +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 + | |-- detach_state + | |-- device + | |-- irq + | |-- local_cpus + | |-- resource + | |-- resource0 + | |-- resource1 + | |-- resource2 + | |-- rom + | |-- subsystem_device + | |-- subsystem_vendor + | `-- vendor + `-- detach_state + +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) + detach_state connection status (bool, 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. +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. + +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.
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