Re: [PATCH 1/4] RISC-V: use bit-values instead of numbers to identify patched cpu-features

[Conor Dooley <conor@kernel.org>]

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On Fri, Jan 13, 2023 at 10:23:48PM +0100, Heiko Stuebner wrote:
> From: Heiko Stuebner <heiko.stuebner@vrull.eu>
> 
> RISC-V cpufeatures are often based on available extensions and maybe even
> some combination of them. Using a bitfield for the errata-id gives us a
> simple way to also require a combination of extensions for a specific
> alternative patch.
> 
> Signed-off-by: Heiko Stuebner <heiko.stuebner@vrull.eu>
> ---

> diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> index 7bfc6eb9a5cf..8c83bd9d0e22 100644
> --- a/arch/riscv/kernel/cpufeature.c
> +++ b/arch/riscv/kernel/cpufeature.c
> @@ -350,13 +350,13 @@ static u32 __init_or_module cpufeature_probe(unsigned int stage)
>  	u32 cpu_req_feature = 0;
>  
>  	if (cpufeature_probe_svpbmt(stage))
> -		cpu_req_feature |= BIT(CPUFEATURE_SVPBMT);
> +		cpu_req_feature |= CPUFEATURE_SVPBMT;
>  
>  	if (cpufeature_probe_zicbom(stage))
> -		cpu_req_feature |= BIT(CPUFEATURE_ZICBOM);
> +		cpu_req_feature |= CPUFEATURE_ZICBOM;

I know the behaviour isn't changing here, but using a bit per feature
seems like scarily few, especially if people come along with variants
they want for all the various dinky extensions that exit.
Probably gonna need an iteration on this stuff in the not-too-distant
future...


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