[RFC PATCH] implement read_cpuid_ext for v7-M (Was: Re: [PATCHv2 2/3] ARM: Detect support for SDIV/UDIV from ISAR0) register

[Will Deacon]

On Tue, May 07, 2013 at 10:35:08AM +0100, Uwe Kleine-König wrote:
> Hello Will,

Hello,

> On Tue, May 07, 2013 at 10:22:09AM +0100, Will Deacon wrote:
> > On Mon, May 06, 2013 at 10:30:59AM +0100, Uwe Kleine-König wrote:
> > > +#elif defined(CONFIG_CPU_V7M)
> > > +
> > > +#include <asm/io.h>
> > > +#include <asm/v7m.h>
> > > +
> > > +#define read_cpuid(reg)							\
> > > +	({								\
> > > +		WARN_ON_ONCE(1);					\
> > > +		0;							\
> > > +	})
> > 
> > We do have an MIDR in PMSAv7 (not to be confused with MPIDR), so why not read
> > that here?
> I don't know it and it's unrelated to this patch. But I will note it and
> check it. In the meantime I'm taking patches of course :-)

I don't think it is unrelated to this patch: I'm suggesting that you add an
MIDR read to read_cpuid, instead of the unconditional WARN_ON_ONCE which
you're adding here.

Then you can remove your v7m-specific read_cpuid_id implementation, because
read_cpuid(CPUID_ID) will do the right thing.

...or am I missing something?

Will