Re: [PATCH v3] arm: remove !CPU_V6 and !GENERIC_ATOMIC64 builddependencies for XEN

[Stefano Stabellini]

On Thu, 9 Jan 2014, Arnd Bergmann wrote:
> On Thursday 09 January 2014, Will Deacon wrote:
> > On Wed, Jan 08, 2014 at 06:00:23PM +0000, Stefano Stabellini wrote:
> > > Remove !GENERIC_ATOMIC64 build dependency:
> > > - rename atomic64_xchg to armv7_atomic64_xchg and define it even ifdef
> > >   GENERIC_ATOMIC64;
> > > - call armv7_atomic64_xchg directly from xen/events.h.
> > > 
> > > Remove !CPU_V6 build dependency:
> > > - introduce __cmpxchg8 and __cmpxchg16, compiled even ifdef
> > >   CONFIG_CPU_V6;
> > > - implement sync_cmpxchg using __cmpxchg8 and __cmpxchg16.
> > > 
> > > Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> > > CC: arnd@xxxxxxxx
> > > CC: linux@xxxxxxxxxxxxxxxx
> > > CC: will.deacon@xxxxxxx
> > > CC: gang.chen@xxxxxxxxxxx
> > > CC: catalin.marinas@xxxxxxx
> > > CC: jaccon.bastiaansen@xxxxxxxxx
> > > CC: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> > > CC: linux-kernel@xxxxxxxxxxxxxxx
> > > 
> > 
> > I'm confused here. It looks like you want to call armv7 code in a v6 kernel.
> > What am I missing?
> 
> This is about being able to build a kernel that runs on ARMv6 and ARMv7
> and also includes Xen. Because of obvious hardware limitations, Xen
> will only run on v7, but currently you cannot even build it once you
> enable (pre-v6K) ARMv6 support, since the combined v6+v7 kernel can't
> do atomic accesses in a generic way on non-32bit variables.

Yep, that's right.
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