[PATCH] ARM support single byte cmpxchg and cmpxchg_local on ARMv6

[mathieu.desnoyers@polymtl.ca (Mathieu Desnoyers)]

* Russell King - ARM Linux (linux at arm.linux.org.uk) wrote:
> On Wed, Mar 10, 2010 at 03:02:36PM -0500, Mathieu Desnoyers wrote:
> > * Russell King - ARM Linux (linux at arm.linux.org.uk) wrote:
> > > On Wed, Mar 10, 2010 at 06:22:21PM +0200, Imre Deak wrote:
> > > > recently you've added support for __cmpxchg for ARMv6+. There the assumption
> > > > is that ldrex[bh]/strex[bh] is only supported on platforms with the 32v6K
> > > > extension.
> > > > 
> > > > Currently the __xchg code uses these even without the extension. Should this
> > > > be fixed?
> > > 
> > > From what I remember, the half-word versions definitely aren't supported
> > > on anything without V6K extensions.  I think that the byte and word
> > > versions are supported on V6 and up though.
> > > 
> > > That'd make both __cmpxchg and __xchg slightly buggy, in different ways.
> > > 
> > > What it does mean is that atomic operations on unsigned shorts using
> > > ldrex/strex will only be possible on V6K and up.
> > 
> > Does the following help (addressing the single byte cmpxchg part of the
> > problem) ?
> 
> First I'd need to look up what the real conditions are on the ldrex
> instructions - which I'm not doing at the moment on account of being
> down with the lurgy this week...

No problem, the patch can wait.

Take care,

Mathieu



-- 
Mathieu Desnoyers
Operating System Efficiency Consultant
EfficiOS Inc.
http://www.efficios.com