netdev - Re: [PATCH net-next-2.6 1/2] be2net: Adding an option to use INTx instead of MSI-X

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Message-ID: <20101028053714.GD32200@lackof.org>
Date:	Wed, 27 Oct 2010 23:37:14 -0600
From:	Grant Grundler <grundler@...isc-linux.org>
To:	David Miller <davem@...emloft.net>
Cc:	michael@...erman.id.au, bhutchings@...arflare.com,
	somnath.kotur@...lex.com, netdev@...r.kernel.org,
	linux-pci@...r.kernel.org
Subject: Re: [PATCH net-next-2.6 1/2] be2net: Adding an option to use INTx
	instead of MSI-X

On Wed, Oct 27, 2010 at 08:46:04AM -0700, David Miller wrote:
> From: Michael Ellerman <michael@...erman.id.au>
> Date: Wed, 27 Oct 2010 10:20:35 +1100
> 
> > On Tue, 2010-10-26 at 14:32 +0100, Ben Hutchings wrote:
> >> Michael Ellerman wrote:
> >> > On Mon, 2010-10-25 at 16:25 -0700, David Miller wrote:
> >> > > From: Ben Hutchings <bhutchings@...arflare.com>
> >> > > Date: Mon, 25 Oct 2010 23:38:53 +0100
> > 
> >> > Ethtool would be nice, but only for network drivers. Is there a generic
> >> > solution, quirks are obviously not keeping people happy.
> >>  
> >> Since this is (normally) a property of the system, pci=nomsi is the
> >> generic solution.
> > 
> > Sort of, it's a big hammer. Did all these driver writers not know about
> > pci=nomsi or did they prefer to add a parameter to their driver for some
> > reason?
> 
> Every time I've actually done the work to try and track down the
> true issue, it always turned out to be a PCI chipset problem rather
> than a device specific issue.

I agree with your generalization. I can think of only one exception:
ISTR pre-5705 tg3 chips would send both MSI and assert IRQ line at the same time.

My guess is driver writers just want knob to "work around" any issues
*their* driver might see with chipset. Disabling MSI for all drivers
doesn't leave opportunity for experimenting with individual drivers.

hth,
grant

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