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SubjectRe: [PATCH] pci: increase alignment to make more space for hidden code
Bjorn Helgaas wrote:
> On Sunday 11 October 2009 03:17:16 pm Yinghai Lu wrote:
>> for
>>
>> http://bugzilla.kernel.org/show_bug.cgi?id=13940
>>
>> some system when acpi are enabled, acpi clears some BAR for some devices without
>> reason, and kernel will need to allocate devices for them.
>
> "ACPI clears some BARs"? I'm dubious. The handoff state is the same
> whether we boot with "acpi=off" or not, so the BIOS can't be clearing
> them. I really don't think the ACPI code in Linux clears BARs. The
> Linux PCI code might be clearing BARs, but it sure would be nice to
> know exactly why. Did you ever figure that out?

please check the mail is reponsed to Ingo.

>
>> try to increase alignment to get more safe range for unassigned devices.
>>
>> Signed-off-by: Yinghai Lu <yinghai@kernel.org>
>>
>> ---
>> arch/x86/kernel/e820.c | 4 ++--
>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> Index: linux-2.6/arch/x86/kernel/e820.c
>> ===================================================================
>> --- linux-2.6.orig/arch/x86/kernel/e820.c
>> +++ linux-2.6/arch/x86/kernel/e820.c
>> @@ -1378,8 +1378,8 @@ static unsigned long ram_alignment(resou
>> if (mb < 16)
>> return 1024*1024;
>>
>> - /* To 32MB for anything above that */
>> - return 32*1024*1024;
>> + /* To 64MB for anything above that */
>> + return 64*1024*1024;
>
> How do we know 64MB is the correct alignment?
>
> This feels like a hack that accidentally covers up the problem. I
> don't think we understand what's happening well enough.

yes, we need to figure out why when acpi=on, those BAR are cleared, before pci code try to scan and read BAR.
(node early pic print out untouched, but after APCI subsystem is enabled, those BAR got clearred)

YH


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