Re: [PATCH v3 4/8] RISC-V: Check Zicclsm to set unaligned access speed

[Conor Dooley <conor@kernel.org>]

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On Mon, Jun 24, 2024 at 08:49:57PM -0400, Jesse Taube wrote:
> Check for Zicclsm before checking for unaligned access speed. This will
> greatly reduce the boot up time as finding the access speed is no longer
> necessary.
> 
> Signed-off-by: Jesse Taube <jesse@rivosinc.com>
> ---
> V2 -> V3:
>  - New patch split from previous patch
> ---
>  arch/riscv/kernel/unaligned_access_speed.c | 26 ++++++++++++++--------
>  1 file changed, 17 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/riscv/kernel/unaligned_access_speed.c b/arch/riscv/kernel/unaligned_access_speed.c
> index a9a6bcb02acf..329fd289b5c8 100644
> --- a/arch/riscv/kernel/unaligned_access_speed.c
> +++ b/arch/riscv/kernel/unaligned_access_speed.c
> @@ -259,23 +259,31 @@ static int check_unaligned_access_speed_all_cpus(void)
>  	kfree(bufs);
>  	return 0;
>  }
> +#else /* CONFIG_RISCV_PROBE_UNALIGNED_ACCESS */
> +static int check_unaligned_access_speed_all_cpus(void)
> +{
> +	return 0;
> +}
> +#endif
>  
>  static int check_unaligned_access_all_cpus(void)
>  {
> -	bool all_cpus_emulated = check_unaligned_access_emulated_all_cpus();
> +	bool all_cpus_emulated;
> +	int cpu;
> +
> +	if (riscv_has_extension_unlikely(RISCV_ISA_EXT_ZICCLSM)) {
> +		for_each_online_cpu(cpu) {
> +			per_cpu(misaligned_access_speed, cpu) = RISCV_HWPROBE_MISALIGNED_FAST;

- const: zicclsm
  description:
    The standard Zicclsm extension for misaligned support for all regular
    load and store instructions (including scalar and vector) but not AMOs
    or other specialized forms of memory access. Defined in the
    RISC-V RVA Profiles Specification. 

Doesn't, unfortunately, say anywhere there that they're actually fast :(

Thanks,
Conor.

> +		}
> +		return 0;
> +	}
> +
> +	all_cpus_emulated = check_unaligned_access_emulated_all_cpus();
>  
>  	if (!all_cpus_emulated)
>  		return check_unaligned_access_speed_all_cpus();
>  
>  	return 0;
>  }
> -#else /* CONFIG_RISCV_PROBE_UNALIGNED_ACCESS */
> -static int check_unaligned_access_all_cpus(void)
> -{
> -	check_unaligned_access_emulated_all_cpus();
> -
> -	return 0;
> -}
> -#endif
>  
>  arch_initcall(check_unaligned_access_all_cpus);
> -- 
> 2.45.2
> 

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