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

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Date:	Thu, 13 Dec 2007 10:24:24 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Ivan Kokshaysky <ink@...assic.park.msu.ru>
Cc:	Robert Hancock <hancockr@...w.ca>, benh@...nel.crashing.org,
	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

> So disabling memory or IO decode in a command register seems to be
> the only safe option. This depends on architecture, though.

You are assuming a degree of sanity that seems unwise (at least for PC
class hardware).

Whether a given BAR is decoded depends not only on the contents of the
BAR but also the hardware configuration *specific* to the device.

The SIL680 for example has an MMIO BAR at BAR5. Control for that BAR is
via MMIO_EN which is a bit in PCI config register 0x8A.

So if we disable the device because of a dangling BAR the users root file
system goes away. If we leave it as is we have to know the
firmware/hardware came up with that BAR disabled or how to control it at
a per device level.

Supporting pci_enable_device_io / pci_enable_device_mmio / pci_iomap_io /
pci_iomap_mmio seems to cover pretty much all the use cases we have. 

The users we have right now that are:

	- pata_cs5520   (can be dealt with easily)
	- old IDE	(with the new resource handling for legacy IDE
can use pci_enable_device_io I think, ditto pci/cs5520)
	- scx200_acb	(looks like a simple substitution works)
	- lpfc		pci_enable_device_mmio
	- qla2xxx	pci_enable_device ? (enables IO and MMIO)

Alan
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