[PATCH v3 4/5] arm64: alternative: Introduce feature for GICv3 CPU interface

[christoffer.dall@linaro.org (Christoffer Dall)]

On Fri, Mar 27, 2015 at 01:09:24PM +0000, Marc Zyngier wrote:
> Add a new item to the feature set (ARM64_HAS_SYSREG_GIC_CPUIF)
> to indicate that we have a system register GIC CPU interface
> 
> This will help KVM switching to alternative instruction patching.
> 
> Reviewed-by: Andre Przywara <andre.przywara@arm.com>
> Acked-by: Will Deacon <will.deacon@arm.com>
> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
> ---
>  arch/arm64/include/asm/cpufeature.h |  8 +++++++-
>  arch/arm64/kernel/cpufeature.c      | 16 ++++++++++++++++
>  2 files changed, 23 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
> index 6ae35d1..d9e57b5 100644
> --- a/arch/arm64/include/asm/cpufeature.h
> +++ b/arch/arm64/include/asm/cpufeature.h
> @@ -23,8 +23,9 @@
>  
>  #define ARM64_WORKAROUND_CLEAN_CACHE		0
>  #define ARM64_WORKAROUND_DEVICE_LOAD_ACQUIRE	1
> +#define ARM64_HAS_SYSREG_GIC_CPUIF		2
>  
> -#define ARM64_NCAPS				2
> +#define ARM64_NCAPS				3
>  
>  #ifndef __ASSEMBLY__
>  
> @@ -37,6 +38,11 @@ struct arm64_cpu_capabilities {
>  			u32 midr_model;
>  			u32 midr_range_min, midr_range_max;
>  		};
> +
> +		struct {	/* Feature register checking */
> +			u64 register_mask;
> +			u64 register_value;
> +		};
>  	};
>  };
>  
> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index 3d9967e..b0bea2b3 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -22,7 +22,23 @@
>  #include <asm/cpu.h>
>  #include <asm/cpufeature.h>
>  
> +static bool
> +has_id_aa64pfr0_feature(const struct arm64_cpu_capabilities *entry)
> +{
> +	u64 val;
> +
> +	val = read_cpuid(id_aa64pfr0_el1);

is this preferred compared to fishing it out of cpuinfo ?

> +	return (val & entry->register_mask) == entry->register_value;
> +}
> +
>  static const struct arm64_cpu_capabilities arm64_features[] = {
> +	{
> +		.desc = "system register GIC CPU interface",
> +		.capability = ARM64_HAS_SYSREG_GIC_CPUIF,
> +		.matches = has_id_aa64pfr0_feature,
> +		.register_mask = (0xf << 24),
> +		.register_value = (1 << 24),

I don't know if it's worth defining these masks in some header file.
The only other place I could see them used was in head.S.

> +	},
>  	{},
>  };
>  
> -- 
> 2.1.4
> 

Besides the nits, this looks good to me.

-Christoffer