linux-kernel - Re: [patches] [patch 3/5] x86: Add PCI extended config space access for AMD Barcelona

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Message-ID: <20070903083242.GA22144@alberich.amd.com>
Date:	Mon, 3 Sep 2007 10:32:42 +0200
From:	"Andreas Herrmann" <andreas.herrmann3@....com>
To:	"Andi Kleen" <ak@...e.de>
cc:	"Robert Richter" <robert.richter@....com>, patches@...-64.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patches] [patch 3/5] x86: Add PCI extended config space
 access for AMD Barcelona

On Sat, Sep 01, 2007 at 12:11:52PM +0200, Andi Kleen wrote:
> On Thursday 30 August 2007 19:43:14 Robert Richter wrote:
> > This patch implements PCI extended configuration space access for
> > AMD's Barcelona CPUs. It extends the method using CF8/CFC IO
> > addresses. An x86 capability bit has been introduced that is set for
> > CPUs supporting PCI extended config space accesses.
> 
> We shouldn't need this because extended config space should work
> here and Linux should use it 
> (especially after we added the ugly Barcelona workaround into  that code) 

This patch is needed for all buggy BIOSes that don't correctly set up MCFG.

> The only exception would be if the user disables MMCONFIG in CONFIG, but that's
> their own fault then.

No, as you stated yourself there are two exceptions. And the more serious one is the
BIOS issue.

> Ok there might be buggy BIOS around with no or no usable MCFG table, but since
> extended config space is not really a critical feature that's not a big issue.

Not sure why you assume extended config space (ECS) is not critical.
Ok, for a lot of stuff it does not matter.
But it is needed for some devices for full functionality.
E.g. for perfmon (family 0x10/extended inerrupts) extended config space access
is a prerequisite.

> So I don't think we want this special case code at all and should
> just rely on MMCONFIG.

Rely on something unreliable (due to buggy/incomplete BIOS)?
I don't think we should do this.

IMHO it is best to try to use MMCONFIG if it's working and to use
a fallback (e.g. CF8 ECS access for family 0x10) if available.


Regards,

Andreas

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