linux-kernel - Re: [Patch v2] Make PCI extended config space (MMCONFIG) a driver opt-in

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Date:	Fri, 11 Jan 2008 11:54:56 -0800
From:	Arjan van de Ven <arjan@...radead.org>
To:	Greg KH <greg@...ah.com>
Cc:	linux-kernel@...r.kernel.org, Jeff Garzik <jeff@...zik.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>, gregkh@...e.de,
	inux-pci@...ey.karlin.mff.cuni.cz,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Martin Mares <mj@....cz>, Matthew Wilcox <matthew@....cx>
Subject: Re: [Patch v2] Make PCI extended config space (MMCONFIG) a driver
 opt-in

On Fri, 11 Jan 2008 11:02:29 -0800
Greg KH <greg@...ah.com> 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 <arjan@...ux.intel.com>
+Description:
+		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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