linux-kernel - Re: [PATCH-RFC 1/2] tile: don't panic on iomap

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Date:	Wed, 30 Nov 2011 18:32:11 +0000
From:	Arnd Bergmann <arnd@...db.de>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	Chris Metcalf <cmetcalf@...era.com>,
	Lucas De Marchi <lucas.demarchi@...fusion.mobi>,
	Paul Mundt <lethal@...ux-sh.org>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	"David S. Miller" <davem@...emloft.net>,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
	linux-arch@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH-RFC 1/2] tile: don't panic on iomap

On Wednesday 30 November 2011, Michael S. Tsirkin wrote:
> On Wed, Nov 30, 2011 at 03:49:57PM +0000, Arnd Bergmann wrote:
> > On Wednesday 30 November 2011, Michael S. Tsirkin wrote:
> > > On Wed, Nov 30, 2011 at 02:04:41PM +0000, Arnd Bergmann wrote:
> > >
> > > > Ah, right. I didn't realize that the generic pci_iomap still attempts
> > > > to call ioport_map(). It would probably make sense to enclose
> > > > the ioport_map() call in pci_iomap() inside of #ifdef CONFIG_HAS_IOPORT.
> > > > It's not exactly beautiful, but probably the most correct solution
> > > > so that we can make any call to ioport_map() a build-time error on
> > > > architectures that set CONFIG_NO_IOPORT.
> > > 
> > > I'm not sure why do you want to do that.
> > > 
> > 
> > The problem is that any definition of ioport_map on architectures
> > that can't do it is potentially harmful. Calling panic() is
> > bad style as you pointed out, but simply returning NULL can
> > also be harmful because it's likely that some drivers are written
> > under the (false) assumption that ioport_map can never fail.
> > Getting a build-time error would be more helpful here IMHO.
> 
> Yes but uglifying these users is also bad, ifdefs in code are incredibly
> fragile. Isn't it enough to declare ioport_map __must_check?

I guess we already wasted too many electrons over this triviality,
I don't actually care all that much, and will probably have to
touch the same code again when I get to submit my patch to make
inb/outb optional for architectures. Just pick any solution (including
your original one). I'll revisit this when I'm bothered by the
presence of the ioport_map function and will keep you in the loop
on those patches.

	Arnd
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