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

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Date:	Sun, 15 Oct 2006 22:52:15 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Andrew Morton <akpm@...l.org>
Cc:	Matthew Wilcox <matthew@....cx>,
	David Brownell <david-b@...bell.net>,
	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: [Bulk] Re: [PATCH 1/2] [PCI] Check that MWI bit really did get
	set

Ar Sul, 2006-10-15 am 10:45 -0700, ysgrifennodd Andrew Morton:
> If the drivers doesn't care and if it makes no difference to performance
> then just delete the call to pci_set_mwi().
> 
> But if MWI _does_ make a difference to performance then we should tell
> someone that it isn't working rather than silently misbehaving?

It isn't misbehaving it just isn't available. MWI is rather different to
say pci_set_master() in that it makes a lot of sense for many drivers to
ask for it but not care about the results. Something like pci_set_master
failing is a big problem and has to be handled (although as we often
don't use BIOS PCI services we see fake success in some cases).

MWI is an "extra cheese" option not a "no pizza" case

Alan

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