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

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Message-ID: <20071224080922.GE3758@colo.lackof.org>
Date:	Mon, 24 Dec 2007 01:09:22 -0700
From:	Grant Grundler <grundler@...isc-linux.org>
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]

On Sun, Dec 23, 2007 at 03:16:24PM -0500, 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?).

You are missing some history... I posted such a patch in 2002:
    http://lkml.org/lkml/2002/12/19/145

> 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).

ISTR willy or Ivan recently posted a patch that was suggested in 2002
as well (don't disable MMIO on bridge devices when sizing BARs)...so the
main objections might be resolved to this "obvious fix". *sigh*

> 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).

Thanks for posting the traces...it's past midnight here and I'll try to
look at those tomorrow. (Sorry - sounds like a lame excuse but I'm likely
to read the trace incorrectly at the moment.)

cheers,
grant
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