[PATCH V10 2/6] arm: arm64: Add routine to determine cpuid of other cpus

[Russell King - ARM Linux]

On Tue, Nov 29, 2016 at 10:31:12AM +0000, Will Deacon wrote:
> [adding Russell]
> 
> On Wed, Nov 09, 2016 at 05:39:49PM -0600, Jeremy Linton wrote:
> > It is helpful if we can read the cpuid/midr of other CPUs
> > in the system independent of arm/arm64.
> > 
> > Signed-off-by: Jeremy Linton <jeremy.linton at arm.com>
> > ---
> >  arch/arm/include/asm/cputype.h   | 2 ++
> >  arch/arm64/include/asm/cputype.h | 3 +++
> >  2 files changed, 5 insertions(+)
> > 
> > diff --git a/arch/arm/include/asm/cputype.h b/arch/arm/include/asm/cputype.h
> > index 522b5fe..31fb273 100644
> > --- a/arch/arm/include/asm/cputype.h
> > +++ b/arch/arm/include/asm/cputype.h
> > @@ -235,6 +235,8 @@ static inline unsigned int __attribute_const__ read_cpuid_mpidr(void)
> >  #define cpu_is_sa1100() (read_cpuid_part() == ARM_CPU_PART_SA1100)
> >  #define cpu_is_sa1110() (read_cpuid_part() == ARM_CPU_PART_SA1110)
> >  
> > +#define read_specific_cpuid(cpu_num) per_cpu_ptr(&cpu_data, cpu_num)->cpuid
> > +
> >  /*
> >   * Intel's XScale3 core supports some v6 features (supersections, L2)
> >   * but advertises itself as v5 as it does not support the v6 ISA.  For
> 
> Russell -- are you ok with adding this macro to arch/arm/? It will get used
> by the CPU PMU driver, which needs a portable (i.e. between arm and arm64)
> way to convert a logical CPU ID into the MIDR register for that CPU.

No, because we don't set the cpuid member in uniprocessor configurations,
so it's going to be a fragile macro - it'll return zero for kernels
configured without SMP support.

I'd ideally like cpuid for the boot CPU to be set early, so that we can
get rid of many ifdefs in this area, but haven't convinced myself that
it's safe to do so in all configurations with the percpu stuff not being
up and running in setup_arch().

-- 
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