[PATCH v12 08/40] arm64/sme: Manually encode SME instructions

[Catalin Marinas]

On Fri, Feb 25, 2022 at 04:58:51PM +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>

Reviewed-by: Catalin Marinas <catalin.marinas at arm.com>