[PATCH v1 4/5] RISC-V: hwprobe: Support probing of misaligned accesss performance

[Heiko Stübner]

Am Donnerstag, 13. Oktober 2022, 18:35:50 CET schrieb Palmer Dabbelt:
> This allows userspace to select various routines to use based on the
> performance of misaligned access on the target hardware.
> 
> Signed-off-by: Palmer Dabbelt <palmer at rivosinc.com>

[...]

> diff --git a/arch/riscv/include/asm/cpufeature.h b/arch/riscv/include/asm/cpufeature.h
> index cbda062de9bd..54bdcf9a5049 100644
> --- a/arch/riscv/include/asm/cpufeature.h
> +++ b/arch/riscv/include/asm/cpufeature.h
> @@ -18,4 +18,6 @@ struct riscv_cpuinfo {
>  
>  DECLARE_PER_CPU(struct riscv_cpuinfo, riscv_cpuinfo);
>  
> +DECLARE_PER_CPU(long, misaligned_access_speed);

just my 2ct ... wouldn't it make sense to have struct riscv_cpuinfo
as the central instance for all cpu-related stuff, so
misaligned_access_speed could also be part of it?


> diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> index 553d755483ed..1599e40cd170 100644
> --- a/arch/riscv/kernel/cpufeature.c
> +++ b/arch/riscv/kernel/cpufeature.c
> @@ -222,6 +226,22 @@ void __init riscv_fill_hwcap(void)
>  			bitmap_copy(riscv_isa, this_isa, RISCV_ISA_EXT_MAX);
>  		else
>  			bitmap_and(riscv_isa, riscv_isa, this_isa, RISCV_ISA_EXT_MAX);
> +
> +		/*
> +		 * Check for the performance of misaligned accesses.
> +		 */
> +		cpu = hartid_to_cpuid_map(hartid);
> +		if (cpu < 0)
> +			continue;
> +
> +		if (of_property_read_string(node, "riscv,misaligned-access-performance", &misaligned)) {

I think this wants a "!" in front :-) .

of_property_read_string() returns 0 on success, so running this
results in a nullptr right now.

> +			if (strcmp(misaligned, "emulated") == 0)
> +				per_cpu(misaligned_access_speed, cpu) = RISCV_HWPROBE_MISALIGNED_EMULATED;
> +			if (strcmp(misaligned, "slow") == 0)
> +				per_cpu(misaligned_access_speed, cpu) = RISCV_HWPROBE_MISALIGNED_SLOW;
> +			if (strcmp(misaligned, "fast") == 0)
> +				per_cpu(misaligned_access_speed, cpu) = RISCV_HWPROBE_MISALIGNED_FAST;
> +		}
>  	}
>  
>  	/* We don't support systems with F but without D, so mask those out


Heiko