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

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Message-Id: <20071022.171318.104036671.davem@davemloft.net>
Date:	Mon, 22 Oct 2007 17:13:18 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	barkalow@...ervon.org
Cc:	jeff@...zik.org, linas@...tin.ibm.com, chunhao.huang@...mail.com,
	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@...i.com
Subject: Re: [patch] PCI: disable MSI on more ATI NorthBridges

From: Daniel Barkalow <barkalow@...ervon.org>
Date: Mon, 22 Oct 2007 17:31:04 -0400 (EDT)

> It's likewise documented (although maybe arguable in wording) that the 
> device shouldn't send legacy interrupts if MSI is in use, regardless of 
> INTX_DISABLE, but this also happens in the field.
> 
> I think that the current Linux behavior with respect to INTX_DISABLE is 
> simply due to which hardware bug was present in the device whose driver 
> first got Linux support, but one or the other or both needs a quirk, since 
> there's no behavior that works with everything. And it's still impossible 
> to tell which bug is more common, since MSI isn't used most of the time, 
> even if the hardware supports it, so it's pretty arbitrary which way Linux 
> goes in the non-quirk case.

I think this pretty much sums up the situation accurately.

My suggestion is:

1) Leave the pci_intx() twiddling code in drivers/pci/msi.c

2) Add quirks for "INTX_DISABLE turns off MSI too", this sets
   a flag in the pci_dev.

3) The pci_intx() calls in drivers/pci/msi.c are skipped if this
   flag from #2 is set.

4) Add quirk entries for drivers/net/tg3.c chips and these SATA
   devices we are learning about here, as well as any others we
   are aware of right now.

5) Remove the pci_intx() workaround code from drivers/net/tg3.c
   and elsewhere.
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