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SubjectRe: [PATCH v2 08/31] arm64: CPU support
On Wed, Aug 15, 2012 at 01:10:43AM +0100, Olof Johansson wrote:
> On Tue, Aug 14, 2012 at 06:52:09PM +0100, Catalin Marinas wrote:
>
> > diff --git a/arch/arm64/include/asm/cputype.h b/arch/arm64/include/asm/cputype.h
> > new file mode 100644
> > index 0000000..ef54125
> > --- /dev/null
> > +++ b/arch/arm64/include/asm/cputype.h
> > @@ -0,0 +1,49 @@
> > +#define ID_MIDR_EL1 "midr_el1"
> > +#define ID_CTR_EL0 "ctr_el0"
> > +
> > +#define ID_AA64PFR0_EL1 "id_aa64pfr0_el1"
> > +#define ID_AA64DFR0_EL1 "id_aa64dfr0_el1"
> > +#define ID_AA64AFR0_EL1 "id_aa64afr0_el1"
> > +#define ID_AA64ISAR0_EL1 "id_aa64isar0_el1"
> > +#define ID_AA64MMFR0_EL1 "id_aa64mmfr0_el1"
> > +
> > +#define read_cpuid(reg) ({ \
> > + u64 __val; \
> > + asm("mrs %0, " reg : "=r" (__val)); \
> > + __val; \
> > +})
> > +
> > +/*
> > + * The CPU ID never changes at run time, so we might as well tell the
> > + * compiler that it's constant. Use this function to read the CPU ID
> > + * rather than directly reading processor_id or read_cpuid() directly.
> > + */
> > +static inline u32 __attribute_const__ read_cpuid_id(void)
> > +{
> > + return read_cpuid(ID_MIDR_EL1);
> > +}
> > +
> > +static inline u32 __attribute_const__ read_cpuid_cachetype(void)
> > +{
> > + return read_cpuid(ID_CTR_EL0);
> > +}
>
> Is this perhaps a carry-over from arch/arm? Abstracting out read_cpuid()
> doesn't seem to buy anything here, just opencode the one-line assembly
> in each.

It doesn't buy much but it's more readable to use read_cpuid() in places
like hw_breakpoint.c than open coding the assembly.

I could get rid of the ID_* macros and just pass the register name
direcly to read_cpuid().

> Might as well cleanup the naming a little too while you're at it, i.e.
> read_cpu_id() and read_cpu_cachetype().

These were defined for convenience, a bit less typing. But they have the
intended name.

> > --- /dev/null
> > +++ b/arch/arm64/mm/proc-syms.c
...
> > +EXPORT_SYMBOL(__cpuc_flush_kern_all);
> > +EXPORT_SYMBOL(__cpuc_flush_user_all);
> > +EXPORT_SYMBOL(__cpuc_flush_user_range);
> > +EXPORT_SYMBOL(__cpuc_coherent_kern_range);
> > +EXPORT_SYMBOL(__cpuc_flush_dcache_area);
>
> See comment on other email about putting function pointers in a struct
> instead.

There is no need to support multiple CPU architectures with different
implementations, so allowing these functions to be called without
indirection is better.

> > diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
> > new file mode 100644
> > index 0000000..453f517
> > --- /dev/null
> > +++ b/arch/arm64/mm/proc.S
> > @@ -0,0 +1,193 @@
> > + .section ".proc.info.init", #alloc, #execinstr
> > +
> > + .type __v8_proc_info, #object
> > +__v8_proc_info:
> > + .long 0x000f0000 // Required ID value
> > + .long 0x000f0000 // Mask for ID
> > + b __cpu_setup
> > + nop
> > + .quad cpu_name
> > + .long 0
> > + .size __v8_proc_info, . - __v8_proc_info
>
> I know this is a carry-over from arch/arm, but how about moving this
> to more of a C construct similar to arch/powerpc/kernel/cputable.c
> instead? It's considerably easier to read that way, and it's convenient
> to have the definitions all in one place, making it easier to share some
> of the functions, etc.

I can do this, it would be indeed cleaner.

--
Catalin


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