[PATCH v2 2/3] arm64: add helper functions to read I-cache attributes

[Will Deacon]

On Tue, Aug 05, 2014 at 10:25:56AM +0100, Ard Biesheuvel wrote:
> This adds helper functions and #defines to <asm/cachetype.h> to read the
> line size and the number of sets from the level 1 instruction cache.
> 
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
> ---
> v2: put () around macro args, use 64-bit types for asm() mrs/msr calls
> 
>  arch/arm64/include/asm/cachetype.h | 28 ++++++++++++++++++++++++++++
>  1 file changed, 28 insertions(+)
> 
> diff --git a/arch/arm64/include/asm/cachetype.h b/arch/arm64/include/asm/cachetype.h
> index 7a2e0762cb40..e59c0c25b307 100644
> --- a/arch/arm64/include/asm/cachetype.h
> +++ b/arch/arm64/include/asm/cachetype.h
> @@ -39,6 +39,34 @@
>  
>  extern unsigned long __icache_flags;
>  
> +#define CCSIDR_EL1_LINESIZE_MASK	0x7
> +#define CCSIDR_EL1_LINESIZE(x)		((x) & CCSIDR_EL1_LINESIZE_MASK)
> +
> +#define CCSIDR_EL1_NUMSETS_SHIFT	13
> +#define CCSIDR_EL1_NUMSETS_MASK		(0x7fff << CCSIDR_EL1_NUMSETS_SHIFT)
> +#define CCSIDR_EL1_NUMSETS(x) \
> +	(((x) & CCSIDR_EL1_NUMSETS_MASK) >> CCSIDR_EL1_NUMSETS_SHIFT)
> +
> +static inline __attribute_const__ u64 icache_get_ccsidr(void)
> +{
> +	u64 ccsidr;
> +
> +	/* Select L1 I-cache and read its size ID register */
> +	asm("msr csselr_el1, %1; isb; mrs %0, ccsidr_el1"
> +	    : "=r"(ccsidr) : "r"(1L));
> +	return ccsidr;

Is it worth having a WARN_ON(preemptible()) here?

Will