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

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Message-Id: <200709031448.42285.ak@suse.de>
Date:	Mon, 3 Sep 2007 14:48:41 +0200
From:	Andi Kleen <ak@...e.de>
To:	"Robert Richter" <robert.richter@....com>
Cc:	"Andreas Herrmann" <andreas.herrmann3@....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 Monday 03 September 2007 13:27, Robert Richter wrote:

> On 03.09.07 12:15:03, Andi Kleen wrote:
> > > But it is needed for some devices for full functionality.
> >
> > Examples? I can only think of PCI express error reporting, which
> > few drivers implement anyways and isn't really a show stopper
> > if it doesn't work. Besides I would be surprised if it even works
> > on the cheap desktop boards which have MCFG less BIOS.
>
> As you say, there are BIOSs that do not support MMCONFIG. Thus, CF8
> access is not only a workaround to boot a system. 

We're talking about accessing the extended part of config spaces. I'm not 
aware of any case where that is required to boot a system.

> Recent (10h) and upcomming CPU families make heavy use of PCI ext cfg
> space for certain CPU features. Setup of the extended interupt local
> vector table for IBS (used with Perfmon2) is one example. CPU
> designers do not take care anymore if a feature is in the base or
> extended config space. So access to PCI ECS is essential.

I don't think it's a big issue if IBS doesn't work on a few buggy BIOS
(which should hopefully become fewer anyways because Vista is out
which actually uses MCFG) 


> > > 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.
> >
> > We only put in workarounds if there is a serious problem otherwise (e.g.
> > not booting etc.). I just don't see this here.
>
> As said above, I do not see CF8 access as a workaround. I expect my
> system to work in the same way also if MMCONFIG is not available.

It should boot sure, but exotic stuff not working is not a major issue

-Andi
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