linux-kernel - Re: [PATCH]PCI:disable resource decode in PCI BAR detection

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Date:	Fri, 14 Sep 2007 19:29:13 +0400
From:	Ivan Kokshaysky <ink@...assic.park.msu.ru>
To:	Robert Hancock <hancockr@...w.ca>
Cc:	Greg KH <gregkh@...e.de>, Matthew Wilcox <matthew@....cx>,
	Shaohua Li <shaohua.li@...el.com>,
	lkml <linux-kernel@...r.kernel.org>,
	linux-pci <linux-pci@...ey.karlin.mff.cuni.cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jesse Barnes <jbarnes@...tuousgeek.org>
Subject: Re: [PATCH]PCI:disable resource decode in PCI BAR detection

On Fri, Sep 14, 2007 at 08:30:59AM -0600, Robert Hancock wrote:
> Do you have an example of specific hardware that exhibits this problem?

Well, first two results of google search for "disable bar when sizing":
 http://lkml.org/lkml/2002/12/21/95
 http://lkml.org/lkml/2002/12/20/110

> So far after a similar patch has been in -mm for months there have been 
> no reports of any such problems.

You cannot compare user base of -mm and release kernels. Also, note
that we're talking about maybe 0.01% of systems running Linux.
And similar patch appeared in various trees several times over the last
decade and every time it had to be reverted.

> This isn't guaranteed to help. I don't think it is only integrated 
> graphics that could cause this problem, I think that an add-on PCI 
> Express card can do this as well. Depending on the chipset memory decode 
> rules, any PCI or PCI Express device with a BAR large enough could cause 
> issues.

No, it's impossible for several reasons. Most obvious one is that a PCI-E
bridge does isolate stuff quite nicely.

Ivan.
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