Reading root bridge resources
From: Rajesh Shah (rajesh.shah_at_intel.com)
Date: 03/31/05
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Date: Wed, 30 Mar 2005 16:24:01 -0800 To: gregkh@suse.de
Greg,
A while back I had volunteered to write a patch that stores the
resource ranges being decoded by root bridges for ACPI based
i386 and x86_64 systems. The thread at:
http://sourceforge.net/mailarchive/message.php?msg_id=10604487
has some context regarding this. The basic intent was to allow
hot-plugged devices sitting directly under a root bridge (versus
under a p2p bridge) to claim the correct resources. The current
code in pci_scan_bus_parented() simply assigns ioport_resource
and iomem_resource to each root bridge, even if it decodes a
subset of those resources.
I did such a patch recently, and ran into problems while testing
it. I made the changes in arch/i386, just like Matthew had done
for arch/ia64. I found that ACPI firmware on some systems was
not reporting the correct resources in the _CRS method per the
ACPI specification. On other systems, there were too many resource
ranges to fit in the 4 slots available in the pci_bus structure.
Getting an inaccurate picture of root bridge resources broke 2 of
my test systems, since some devices failed to claim resources at
boot time even though they were otherwise properly configured by
BIOS.
I am therefore inclined to just drop this patch. This may break
hotplug on systems that support hotplug slots directly connected
to the root bridge. If a slot is under a p2p bridge, we already
read bridge bases correctly so this problem does not affect us.
Note however that I was not able to find any such i386 or x86_64
machine anyway. Does somebody have access to such a machine? Any
other suggestions?
Note that a similar patch went into 2.6.11-mm4'ish for ia64. I
haven't heard of any breakage there, so apparently ia64 system
firmware is better behaved.
Rajesh
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