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

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Date:	Fri, 14 Dec 2007 00:12:39 +0300
From:	Ivan Kokshaysky <ink@...assic.park.msu.ru>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
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, 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

	if (pci_enable_device_mmio(dev)) {
		/* failed, fallback to IO */
		if (pci_enable_device_io(dev))
			return -ENODEV;
		...
	}

Ivan.
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