[PATCH v11 08/40] arm64/sme: Manually encode SME instructions

[Catalin Marinas]

On Mon, Feb 07, 2022 at 03:20:37PM +0000, Mark Brown wrote:
> As with SVE rather than impose ambitious toolchain requirements for SME
> we manually encode the few instructions which we require in order to
> perform the work the kernel needs to do. The instructions used to save
> and restore context are provided as assembler macros while those for
> entering and leaving streaming mode are done in asm volatile blocks
> since they are expected to be used from C.
> 
> We could do the SMSTART and SMSTOP operations with read/modify/write
> cycles on SVCR but using the aliases provided for individual field
> accesses should be slightly faster. These instructions are aliases for
> MSR but since our minimum toolchain requirements are old enough to mean
> that we can't use the sX_X_cX_cX_X form and they always use xzr rather
> than taking a value like write_sysreg_s() wants we just use .inst.
> 
> Signed-off-by: Mark Brown <broonie at kernel.org>
> ---
>  arch/arm64/include/asm/fpsimd.h       | 25 +++++++++++++
>  arch/arm64/include/asm/fpsimdmacros.h | 53 +++++++++++++++++++++++++++
>  2 files changed, 78 insertions(+)
> 
> diff --git a/arch/arm64/include/asm/fpsimd.h b/arch/arm64/include/asm/fpsimd.h
> index cb24385e3632..c90f7f99a768 100644
> --- a/arch/arm64/include/asm/fpsimd.h
> +++ b/arch/arm64/include/asm/fpsimd.h
> @@ -249,6 +249,31 @@ static inline void sve_setup(void) { }
>  
>  #endif /* ! CONFIG_ARM64_SVE */
>  
> +#ifdef CONFIG_ARM64_SME
> +
> +static inline void sme_smstart_sm(void)
> +{
> +	asm volatile(".inst 0xd503437f");
> +}
> +
> +static inline void sme_smstop_sm(void)
> +{
> +	asm volatile(".inst 0xd503427f");
> +}
> +
> +static inline void sme_smstop(void)
> +{
> +	asm volatile(".inst 0xd503467f");
> +}

I think you can use xzr with __msr_s. It would be more consistent if we
had some sysregs defined to be used with __msr_s.

-- 
Catalin