linux-kernel - Re: Weirdness in pci_read

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Date:	Mon, 3 Mar 2008 21:29:55 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	benh@...nel.crashing.org
Cc:	Jesse Barnes <jbarnes@...tuousgeek.org>,
	linux-pci@...ey.karlin.mff.cuni.cz,
	Linux Kernel list <linux-kernel@...r.kernel.org>,
	Matthew Wilcox <matthew@....cx>
Subject: Re: Weirdness in pci_read_bases()

> The main question regarding 0 in a BAR is do we know of devices that
> consider it as "disabled" and don't operate/decode 0 ? (That would be
> gross and out of spec but who knows...)

In the PC world it never gets tested so it might be wise to be cautious.

> But that can be solved, using something akin to IORESOURCE_UNSET, like
> we do on powerpc, generalizing it, and having an x86-specific quirk set
> it on anything that comes up with resource->start == 0.

And add pci_resource_unassigned() to wrap it nicely. That would
definitely be a good thing as we have confusion right now and it has
turned up in the real world.

Alan
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