linux-kernel - Re: [PATCH] pci: increase alignment to make more space for hidden code

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Date:	Mon, 12 Oct 2009 11:59:48 -0700
From:	Yinghai Lu <yinghai@...nel.org>
To:	Bjorn Helgaas <bjorn.helgaas@...com>
CC:	Len Brown <lenb@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jesse Barnes <jesse.barnes@...el.com>,
	Ingo Molnar <mingo@...e.hu>,
	Ricardo Jorge da Fonseca Marques Ferreira 
	<storm@...49152.net>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-acpi@...r.kernel.org,
	Yannick Roehlly <yannick.roehlly@...e.fr>,
	Ivan Kokshaysky <ink@...assic.park.msu.ru>, x86@...nel.org
Subject: Re: [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@...nel.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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