Re: [PATCHv3 03/19] arm64: introduce sysreg_clear_set()

[Marc Zyngier <marc.zyngier@arm.com>]

On 18/06/18 13:02, Mark Rutland wrote:
> Currently we have a couple of helpers to manipulate bits in particular
> sysregs:
> 
>  * config_sctlr_el1(u32 clear, u32 set)
> 
>  * change_cpacr(u64 val, u64 mask)
> 
> The parameters of these differ in naming convention, order, and size,
> which is unfortunate. They also differ slightly in behaviour, as
> change_cpacr() skips the sysreg write if the bits are unchanged, which
> is a useful optimization when sysreg writes are expensive.
> 
> Before we gain more yet another sysreg manipulation function, let's
> unify these with a common helper, providing a consistent order for
> clear/set operands, and the write skipping behaviour from
> change_cpacr(). Code will be migrated to the new helper in subsequent
> patches.
> 
> Signed-off-by: Mark Rutland <mark.rutland@arm.com>
> Reviewed-by: Dave Martin <dave.martin@arm.com>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Marc Zyngier <marc.zyngier@arm.com>
> ---
>  arch/arm64/include/asm/sysreg.h | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
> index 48ad361c178e..fefc17dae8ee 100644
> --- a/arch/arm64/include/asm/sysreg.h
> +++ b/arch/arm64/include/asm/sysreg.h
> @@ -731,6 +731,17 @@ asm(
>  	asm volatile("msr_s " __stringify(r) ", %x0" : : "rZ" (__val));	\
>  } while (0)
>  
> +/*
> + * Modify bits in a sysreg. Bits in the clear mask are zeroed, then bits in the
> + * set mask are set. Other bits are left as-is.
> + */
> +#define sysreg_clear_set(sysreg, clear, set) do {			\
> +	u64 __scs_val = read_sysreg(sysreg);				\
> +	u64 __scs_new = (__scs_val & ~(u64)(clear)) | (set);		\
> +	if (__scs_new != __scs_val)					\
> +		write_sysreg(__scs_new, sysreg);			\
> +} while (0)
> +
>  static inline void config_sctlr_el1(u32 clear, u32 set)
>  {
>  	u32 val;
> 

For the record, I have this patch as part of Dave's FPSIMD/SVE fixes.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...