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SubjectRe: [Patch v2] Make PCI extended config space (MMCONFIG) a driver opt-in
On Fri, 11 Jan 2008 11:02:29 -0800
Greg KH <> wrote:

> On Tue, Dec 25, 2007 at 03:26:05AM -0800, Arjan van de Ven wrote:
> >
> > This patch also adds a sysfs property for each device into which
> > root can write a '1' to enable extended configuration space. The
> > kernel will print a notice into dmesg when this happens (including
> > the name of the app) so that if the system crashes as a result of
> > this action, the user can know what action/tool caused it.
> Can you send me a follow-on patch that documents this in
> Documentation/ABI please.

Documentation/ABI/testing/sysfs-pci-extended-config | 39 ++++++++++++++++++++
1 file changed, 39 insertions(+)

Index: linux-2.6.24-rc7/Documentation/ABI/testing/sysfs-pci-extended-config
--- /dev/null
+++ linux-2.6.24-rc7/Documentation/ABI/testing/sysfs-pci-extended-config
@@ -0,0 +1,39 @@
+What: /sys/devices/pci<bus>/<device>/extended_config_space
+Date: January 11, 2008
+Contact: Arjan van de Ven <>
+ This attribute is for use for system-diagnostic software
+ only.
+ The kernel may decide to restrict PCI configuration space
+ access for userspace to the first 64 or 256 bytes by
+ default, for stability reasons. This attribute, when
+ present, can be used to request access to the full
+ 4Kb from the kernel.
+ Request to get access to the full 4Kb can be done by
+ writing a '1' into this attribute file. All other values
+ are reserved for future use and should not be used by
+ software at this point.
+ The kernel may log the request to the various kernel
+ logging services. The kernel may decide to ignore the
+ request if the kernel deems extended configuration space
+ access not reliable enough for the system or the device.
+ The kernel may decide to not present this attribute
+ if the kernel decides extended config space is reliable
+ and made available by default, or if the kernel decides
+ that extended configuration space will never be
+ accessible.
+ Software needs to gracefully deal with getting the
+ access not granted. Software also needs to gracefully deal
+ with this attribute not being present.
+ Due to the fragility of extended configuratio space,
+ system diagnostic software should only set this attribute
+ on explicit user request, or in the case of GUI like tools,
+ at least with explicit user permission.

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