[PATCH 4/4] ARM: hwcap: disable HWCAP_SWP if the CPU advertises it has exclusives

[Russell King - ARM Linux]

On Fri, Jul 04, 2014 at 10:11:06PM +0200, Arnd Bergmann wrote:
> On Friday 04 July 2014 20:52:17 Russell King wrote:
> >         /*
> >          * HWCAP_TLS is available only on 1136 r1p0 and later,
> >          * see also kuser_get_tls_init.
> >          */
> > -       if ((((id >> 4) & 0xfff) == 0xb36) && (((id >> 20) & 3) == 0))
> > +       if (read_cpuid_part() == ARM_CPU_PART_ARM1136 &&
> > +           ((id >> 20) & 3) == 0) {
> >                 elf_hwcap &= ~HWCAP_TLS;
> > +               return;
> > +       }
> > 
> 
> Would it make sense to tie this check to the ARMv6K architecture level?
> 
> I see that cpu_architecture currently reports the same value for plain
> ARMv6 (1136r0) and for ARMv6K (1136r1+ or any other ARM11), but we already
> distinguish them at compile time in a number of places and it seems you
> make the exact same distinction here at runtime.

Hmm, we need guidance from ARM people on that.

There may well be a better way to detect between ARMv6 and ARMv6K, which
is given by the architecture spec.  G7.3 of an early DDI0406 says that
the MPIDR (mp affinity register) aliases to MIDR for ARMv6, but is of
course implemented for ARMv6K.

This seems to be carried through to the latest ARM ARM.  So it seems
this would be a more correct way to tell ARMv6 from ARMv6K.

If so, we can certainly expand cpu_architecture() to detect between the
two and add a CPU_ARCH_ARMv6K in there.

Let's see what Will has to say about that when he's next around...
though I think it'll require another trawl through lots of
documentation.

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