linux-kernel - Re: [patch] PCI: disable MSI on more ATI NorthBridges

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Message-ID: <Pine.LNX.4.64.0710221555190.32497@iabervon.org>
Date:	Mon, 22 Oct 2007 16:26:32 -0400 (EDT)
From:	Daniel Barkalow <barkalow@...ervon.org>
To:	Jeff Garzik <jeff@...zik.org>
cc:	Linas Vepstas <linas@...tin.ibm.com>,
	Shane Huang <chunhao.huang@...mail.com>, davem@...emloft.net,
	gregkh@...e.de, htejun@...il.com, brice.goglin@...il.com,
	david.gaarenstroom@...il.com, linux-kernel@...r.kernel.org,
	linux-pci@...ey.karlin.mff.cuni.cz, shane.huang@....com,
	linux-ide@...r.kernel.org, Brice Goglin <brice@...i.com>
Subject: Re: [patch] PCI: disable MSI on more ATI NorthBridges

On Fri, 19 Oct 2007, Jeff Garzik wrote:

> Linas Vepstas wrote:
> > On Fri, Oct 19, 2007 at 09:17:23PM +0800, Shane Huang wrote:
> > > Since we have little experience on PCI and MSI here, we had to try to
> > 
> > As someone else pointed out, AMD should have *lots* of people with
> > pci and msi experience on the payroll.  (Folks here buy AMD-designed pci
> > chips ...)
> > 
> > > ONLY
> > > comment out the pci_intx() call in drivers/ata/ahci.c
> > > My system can boot up too with MSI enabled!
> > >
> > > So does it mean that the root cause is our SB700 SATA controller
> > > has a hardware bug where setting INTX_DISABLE in the PCI COMMAND
> > > register masks MSI interrupts too? 
> > 
> > That's what it sounds like, to me.
> > 
> > > And what is the software solution or workaround?
> > 
> > Not sure. Sounds like the device driver needs a quirk for this part.
> 
> 
> Take a look at tg3.c net driver change
> 2fbe43f6f631dd7ce19fb1499d6164a5bdb34568 which is a similar situation.
> 
> However, it may turn out that removing the pci_intx() stuff as a general rule
> is easier than quirking these devices, if enough of them turn out to have this
> hardware bug.

At a first approximation, ATI/AMD devices don't send any interrupts if 
intx is disabled, nVidia devices send legacy interrupts in addition to MSI 
ones if intx isn't disabled, and Intel devices actually work correctly. So 
we need at least one kind of device quirk for intx and msi. (And doing it 
in the drivers doesn't work, since everybody is making things driven by 
snd_hda_intel and would like msi, afaict)

	-Daniel
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