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

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Message-ID: <20070903091718.GB22144@alberich.amd.com>
Date:	Mon, 3 Sep 2007 11:17:18 +0200
From:	"Andreas Herrmann" <andreas.herrmann3@....com>
To:	"Arjan van de Ven" <arjan@...radead.org>
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 Mon, Sep 03, 2007 at 01:31:57AM -0700, Arjan van de Ven wrote:
> On Mon, 03 Sep 2007 10:17:39 +0200
> "Robert Richter" <robert.richter@....com> 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.
> > 
> 
> 
> No offence but this feels a bit wrong to me.
> 
> PCI is sort of more a chipset property than a cpu property (I realize
> that this boundary is changing of course).
> 
> I'd like to ask you to at least rename some of the feature bits to
> indicate that the extended config space is for the IO access method;
> after all Linux already supports the MMIO method for accessing extended
> config space since a really long time; not marking the feature bit to
> indicate it's the IO method is going to be extremely confusing and
> cause bugs I bet.

Hmm, yes the naming  of the CPU capability bit seems wrong.
Guess, Robert will fix it.

> (we probably need a global function that drivers can use to find out of
> extended config space is accessible; however that for sure isn't a CPU
> capability bit.

IMHO this is already available. Just check pci_dev->cfg_size which
is 256 if PCI ECS access is not possible (see pci_cfg_space_size()).

> However the current naming etc sort of makes me fear
> drivers will abuse this thing while thinking it's the right API)

Do you see any other issues besides the naming of the bit?


Regards,

Andreas

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