linux-kernel - Re: pci-disable-decode-of-io-memory-during-bar-sizing.patch

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Date:	Tue, 30 Oct 2007 10:28:20 -0700
From:	Arjan van de Ven <arjan@...radead.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Robert Hancock <hancockr@...w.ca>, Greg KH <greg@...ah.com>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	akpm@...ux-foundation.org, ak@...e.de, rajesh.shah@...el.com,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: pci-disable-decode-of-io-memory-during-bar-sizing.patch

On Tue, 30 Oct 2007 10:07:48 -0700 (PDT)
Linus Torvalds <torvalds@...ux-foundation.org> wrote:
> 
> > > The fact is, CONF1 style accesses are just safer, and *work*. 
> > 
> > I would suggest a slight twist then: use CONF1 *until* you're using
> > something above 256, and then and only then switch to MMCONFIG from
> > then on for all accesses.
> 
> No.
> 
> Maybe if you do it per-device, and only *after* probing (ie we have
> seen multiple, and successful, accesses), but globally, absolutely
> not. That would be useless. The bugs we have had in this area have
> been exactly the kinds of things like "we don't know the real size of
> the MMCONFIG areas" etc.

sorry I wasn't very clear, I meant "per device".

> 
> I could easily see device driver writers probing to see if something 
> works, and I absolutely don't think we should just automatically
> enable MMCONFIG from then on.
> 
> But maybe we could have a per-device flag that a driver *can* set. Ie
> have the logic be:
> 
>  - use MMCONFIG if we have to (reg >= 256)
> 
> OR
> 
>  - use MMCONFIG if the driver specifically asked us to

something like
int pci_enable_mmconfig(struct pci_dev *pdev) ?
sounds like a very solid plan to me...


> Maybe somebody inside Intel could just clarify the documentation, and 
> change it from "you're not supposed to mix" to "mix all you want". 

I'll see what I can do ;)


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