linux-kernel - Re: Re: [PATCH 1/2] [PCI] Check that MWI bit really did get set

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Date:	Sun, 15 Oct 2006 12:16:31 -0700
From:	David Brownell <david-b@...bell.net>
To:	alan@...rguk.ukuu.org.uk, matthew@....cx, akpm@...l.org
Cc:	val_henson@...ux.intel.com, netdev@...r.kernel.org,
	linux-pci@...ey.karlin.mff.cuni.cz, linux-kernel@...r.kernel.org,
	gregkh@...e.de
Subject: Re: Re: [PATCH 1/2] [PCI] Check that MWI bit really did get set

(From Alan Cox:)
> The underlying bug is that someone marked pci_set_mwi must-check, that's
> wrong for most of the drivers that use it. If you remove the must check
> annotation from it then the problem and a thousand other spurious
> warnings go away.

Yes, there seems to be abuse of this new "must_check" feature.

(From Andrew Morton:)
> But if MWI _does_ make a difference to performance then we should tell
> someone that it isn't working rather than silently misbehaving?

Thing is, a "difference to performance (alone)" != "misbehavior".

If it affected correctness, then a warning would be appropriate.

Most drivers should be able to say "enable MWI if possible, but
don't worry if it's not possible".  Only a few controllers need
additional setup to make MWI actually work ... if they couldn't
do that setup, that'd be worth a warning before they backed off
to run in a non-MWI mode.

- Dave

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