linux-kernel - Re: [PATCH] Fix coalescing host bridge windows in arch/x86/pci/acpi.c

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Date:	Tue, 24 Sep 2013 11:47:21 +0800
From:	Yijing Wang <wangyijing@...wei.com>
To:	Alexey Neyman <stilor@....net>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Feng Tang <feng.tang@...el.com>, <x86@...nel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Fix coalescing host bridge windows in arch/x86/pci/acpi.c

On 2013/9/23 14:15, Alexey Neyman wrote:
> [Resending due to no response to the original message in a week]
> 
> Hi all,
> 
> I have a board with a BIOS bug that reports the following I/O port regions in 
> _CRS on one of the host bridges:
> 
> 0x0000-0x03af // #0
> 0x03e0-0x0cf7 // #1
> 0x03b0-0x03bb // #2
> 0x03c0-0x03df // #3
> 0x0000-0xdfff // #4
> 0xf000-0xffff // #5
> 
> Obviously, region number #4 is erroneous as it overlaps with regions #0..3. 
> The code in coalesce_windows() in arch/x86/pci/acpi.c attempts to recover from 
> such kind of BIOS bugs by merging the overlapping regions. Current code 
> expands region #0 to 0x0000-0xdffff and makes region #4 ignored. As a result, 
> overlap of the expanded region #0 with regions #1..3 remains undetected (as 
> the inner loop already compared them with region #0). As a result, regions 
> #1..3 are inserted into the resource tree even though they overlap with 
> adjusted region #0 - which later results in resource conflicts for PCI devices 
> with IO ports in one of those regions (e.g., for an PCI IDE controller in 
> legacy mode - which has port 0x3f6). The kernel then refuses to initialize 
> these devices.
> 
> The fix: instead of expanding res1 and ignoring res2, do the opposite. The 
> res2 window is yet to be compared against all windows between res1 and res2 
> (regions #1..3 in the above example), so the resulting resource map will 
> include just the expanded region - and will ignore any overlapping ones.
> 
> Signed-off-by: Alexey Neyman <stilor@....net>
> 

It looks fine to me, but I have no platform to test it. :)


-- 
Thanks!
Yijing

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