linux-kernel - Re: [PATCH v3 00/17] Cross-architecture definitions of relaxed MMIO accessors

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Message-ID: <20141001152356.GA15818@ulmo>
Date:	Wed, 1 Oct 2014 17:23:58 +0200
From:	Thierry Reding <thierry.reding@...il.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Olof Johansson <olof@...om.net>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Will Deacon <will.deacon@....com>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
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Subject: Re: [PATCH v3 00/17] Cross-architecture definitions of relaxed MMIO
 accessors

On Mon, Sep 29, 2014 at 11:50:13AM +0200, Arnd Bergmann wrote:
> On Monday 29 September 2014 10:23:25 Thierry Reding wrote:
> > 
> > How about if I keep iterating this series? It seems like most failures
> > can be reproduced by doing ARM defconfig and allmodconfig builds, so
> > I'll do those and fix up any issues I find. Hopefully I can squash all
> > these before 3.18-rc1, then we can take it into linux-next early for
> > 3.19? In the meantime perhaps I can work with Olof to get a branch with
> > these patches tested on his builder? And perhaps on the 0-day builder in
> > addition?
> 
> Yes, definitely!
> 
> Note that I saw a lot of problems only in randconfig build tests but
> not in any of the default configurations. I'll send you the fixup patch
> soon so you can integrate that in your series.

One of the things I've seen a lot is warnings about volatile being
ignored. This is caused by my latest series dropping the volatile
keyword for the I/O accessors. The rationale being that use of volatile
should be an implementation detail of the accessors rather than the
function signature.

Unfortunately there seems to be a *lot* of code in the kernel that uses
volatile where it probably doesn't make sense. In fact all the warnings
that I've been getting are from code that uses I/O accessors on the I/O
memory, hence shouldn't have to worry about volatile. See also
Documentation/volatile-considered-harmful.txt.

Given the massive amount of changes needed to remove these warnings, is
it better to just keep the volatile keyword even if it's clearly wrong
in the context of the I/O accessors? Or should we bite the bullet and
remove all the wrong uses while at it?

I suppose if we decide to remove them we can always make that a separate
patch series.

Thierry

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