linux-kernel - Re: Possible issue with dangling PCI BARs

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Message-Id: <1197587368.15741.187.camel@pasglop>
Date:	Fri, 14 Dec 2007 10:09:28 +1100
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Ivan Kokshaysky <ink@...assic.park.msu.ru>
Cc:	Jesse Barnes <jesse.barnes@...el.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Robert Hancock <hancockr@...w.ca>,
	linux-pci@...ey.karlin.mff.cuni.cz,
	Linux Kernel list <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: Possible issue with dangling PCI BARs


On Fri, 2007-12-14 at 00:12 +0300, Ivan Kokshaysky wrote:
> On Fri, Dec 14, 2007 at 07:51:06AM +1100, Benjamin Herrenschmidt wrote:
> > If the device is behind a P2P bridge and the BIOS has set the windows of
> > that bridge so tightly that there is no room to allocate the MMIO BAR,
> > then a full disable/full enable would fail on a device that would
> > otherwise work using only PIO.
> 
> It won't be a problem with separate io/mmio enable.
> 
> > However, I'd be curious to see that happening in practice :-)
> > 
> > But I think it's fair enough to do an IO only / MEM only approach. I've
> > seen cases where IO is just not useable because of other constraints and
> > so I expect the MEM-only case to be more common, especially on non-x86.
> 
> Everybody wants MEM if it's available - it's just faster :-)
> So I guess a common case will be

 .../...

Right, I'm going to cook up some patch as time permit, maybe not before
next week tho.

Cheers,
Ben.


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