Re: [kvm-unit-tests PATCH v2 03/10] arm/arm64: smp: support more than 8 cpus

Mark Rutland
2016-06-06T16:32:38Z

On Mon, Jun 06, 2016 at 05:22:49PM +0100, Alex Bennée wrote:
> Andrew Jones <drjones@redhat.com> writes:
> > +#define MPIDR_LEVEL_SHIFT(level) \
> > + (((1 << level) >> 1) << 3)
> > +#define MPIDR_AFFINITY_LEVEL(mpidr, level) \
> > + ((mpidr >> MPIDR_LEVEL_SHIFT(level)) & 0xff)
>
> Doesn't Aff3 break this little macro? It sits at 32:39 with a gap for
> MT, RES0, U, RES1 for bits 25:31

It works, it's just a little bit magic:

(gdb) p (((1 << 0) >> 1) << 3)
$1 = 0
(gdb) p (((1 << 1) >> 1) << 3)
$2 = 8
(gdb) p (((1 << 2) >> 1) << 3)
$3 = 16
(gdb) p (((1 << 3) >> 1) << 3)
$4 = 32
(gdb)

We do the same in arch/arm64/include/asm/cputype.h since b058450f38c337d1
("arm64: kernel: add MPIDR_EL1 accessors macros").

Thanks,
Mark.
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