linux-kernel - Re: [patch -mm] Make check_signature() depend on CONFIG_HAS

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Date:	Thu, 28 Jun 2007 16:01:52 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Jeff Dike <jdike@...toit.com>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	linux-kernel@...r.kernel.org,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Roman Zippel <zippel@...ux-m68k.org>
Subject: Re: [patch -mm] Make check_signature() depend on CONFIG_HAS_IOMEM

On Thu, 28 Jun 2007 18:45:11 -0400
Jeff Dike <jdike@...toit.com> wrote:

> On Thu, Jun 28, 2007 at 11:25:37PM +0100, Alan Cox wrote:
> > This completely bogus. readb() should be present on M68K, fix the
> > platform to implement readb() for MMIO, even if your MMIO readb is a
> > moveb instruction.
> > 
> > check_signature is relevant for anything with MMIO space (for example you
> > can legitimately want to check_signature a MAC68K Nubus ROM).
> > 
> > S/390 is a bit of a special case as no S/390 usage of check_signature
> > appears sane but equally it isn't used so you can stub it out.
> 
> This is a problem for UML too.
> 
> I have a patch in my tree, which basically stubs readb, waiting to see
> how this is fixed for the other arches.
> 

What a mess.

I guess we could add an empty readb() implementation to lib/lib.a so the
arch will pick that up if all else fails.  But it's pretty stinky.  And
it won't work either because we don't know at compile-time to declare
the prototype for that thing appropriately.

So... what's the proper fix here?  "The arch must implement readb"?  That's
bad: if the arch really cannot implement readb(), we want builds to fail
if someone tries to use it.

I think I'll go shopping instead.
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