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

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Message-Id: <1160996576.24237.21.camel@localhost.localdomain>
Date:	Mon, 16 Oct 2006 12:02:56 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Andrew Morton <akpm@...l.org>
Cc:	David Brownell <david-b@...bell.net>, matthew@....cx,
	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: [PATCH 1/2] [PCI] Check that MWI bit really did get set

Ar Sul, 2006-10-15 am 16:44 -0700, ysgrifennodd Andrew Morton:
> Let me restore the words from my earlier email which you removed so that
> you could say that:
> 
>   For you the driver author to make assumptions about what's happening
>   inside pci_set_mwi() is a layering violation.  Maybe the bridge got
>   hot-unplugged.  Maybe the attempt to set MWI caused some synchronous PCI
>   error.  For example, take a look at the various implementations of
>   pci_ops.read() around the place - various of them can fail for various
>   reasons.  

Let me repeat what I said before. As a driver author I do not care. It
doesn't matter if it failed because it is not supported or because a
pink elephant went for a dance on the PCI bus.

>   Now it could be that an appropriate solution is to make pci_set_mwi()
>   return only 0 or 1, and to generate a warning from within pci_set_mwi()
>   if some unexpected error happens.  In which case it is legitimate for
>   callers to not check for errors.

That would be my belief, and ditto for a lot of these other functions -
even the correctly __must_check ones like pci_set_master should do the
error reporting in the set_master() function etc not in every driver.
That gives us a single consistent printk and avoids missing them out or
bloat.

Alan

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