linux-kernel - Re: [Fwd: Re: [PATCH 0/5]PCI: x86 MMCONFIG]

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Date:	Mon, 24 Dec 2007 11:13:55 -0600
From:	Robert Hancock <hancockr@...w.ca>
To:	Loic Prylli <loic@...i.com>
Cc:	Matthew Wilcox <matthew@....cx>, Tony Camuso <tcamuso@...hat.com>,
	Greg KH <gregkh@...e.de>, linux-kernel@...r.kernel.org,
	linux-pci@...ey.karlin.mff.cuni.cz
Subject: Re: [Fwd: Re: [PATCH 0/5]PCI: x86 MMCONFIG]

Loic Prylli wrote:
> I just realized one thing: the bar sizing code in pci_read_bases() (that
> writes 0xffffffff in the bars) does not seem to disable the
> PCI_COMMAND_MEM/PCI_COMMAND_IO bits in the cmd register before
> manipulating the BARs. And it seems nobody else ensures they are
> disabled at this point either (or am I missing something?).

No you're not missing anything. This problem causes many machines to 
break horribly when MMCONFIG is enabled. There's a patch in -mm to fix 
this. (It special-cases the case of host bridges and doesn't disable the 
  decode bits for those, since some are known to do crazy things if you 
do that.)

http://www.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.24-rc6/2.6.24-rc6-mm1/broken-out/pci-disable-decoding-during-sizing-of-bars.patch

> 
> Touching the bars while they are enabled would be buggy behaviour from
> our part, and something trivial to fix. And it might well fix that
> particular problem (it's fair play from the machine to crash if we
> create a decoding conflict, simply disabling the cmd bits in
> pci_read_bases() should remove that conflict).
> 
> FWIW, to partially answer your last question, Windows does disable
> mem-space and/or IO-space when sizing the bars of a device (I have some
> traces of configuration-space-access taken on a window machine for one
> of the PCI busses).

Good to know. There was some speculation that it did not.

-- 
Robert Hancock      Saskatoon, SK, Canada
To email, remove "nospam" from hancockr@...pamshaw.ca
Home Page: http://www.roberthancock.com/

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