[PATCH] PCI: add legacy resources to sysfs for pci busses

This patch adds legacy_io and legacy_mem files to the pci_bus class hierarchy
in sysfs.  The files can be used (if the platform supports them) to access
legacy I/O port space and legacy ISA memory space--useful for things like x86
emulators or VGA card POSTing.  The interfaces are documented in
Documentation/filesystems/sysfs-pci.txt.

Signed-off-by: Jesse Barnes <jbarnes@sgi.com>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>

1 files changed, 25 insertions, 1 deletions

diff --git a/Documentation/filesystems/sysfs-pci.txt b/Documentation/filesystems/sysfs-pci.txt
index 4cabfed6a77d33..e97d024eae77e5 100644
--- a/Documentation/filesystems/sysfs-pci.txt
+++ b/Documentation/filesystems/sysfs-pci.txt
@@ -3,7 +3,7 @@ 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:
 
-     pci0000:17
+     /sys/devices/pci0000:17
      |-- 0000:17:00.0
      |   |-- class
      |   |-- config
@@ -56,9 +56,33 @@ 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.
\ No newline at end of file