linux-kernel - Re: [PATCH 2/9] riscv: Fix riscv_online_cpu

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Message-ID: <1a4de5bb-913d-489a-ac96-3f4dec48cb2d@rivosinc.com>
Date: Fri, 7 Feb 2025 17:47:28 +0100
From: Clément Léger <cleger@...osinc.com>
To: Andrew Jones <ajones@...tanamicro.com>, linux-riscv@...ts.infradead.org,
 linux-kernel@...r.kernel.org
Cc: paul.walmsley@...ive.com, palmer@...belt.com, charlie@...osinc.com,
 jesse@...osinc.com, Anup Patel <apatel@...tanamicro.com>
Subject: Re: [PATCH 2/9] riscv: Fix riscv_online_cpu_vec



On 07/02/2025 17:19, Andrew Jones wrote:
> We shouldn't probe when we already know vector is unsupported and
> we should probe when we see we don't yet know whether it's supported.
> Furthermore, we should ensure we've set the access type to
> unsupported when we don't have vector at all.
> 
> Fixes: e7c9d66e313b ("RISC-V: Report vector unaligned access speed hwprobe")
> Signed-off-by: Andrew Jones <ajones@...tanamicro.com>
> ---
>  arch/riscv/kernel/unaligned_access_speed.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/riscv/kernel/unaligned_access_speed.c b/arch/riscv/kernel/unaligned_access_speed.c
> index b7a8ff7ba6df..161964cf2abc 100644
> --- a/arch/riscv/kernel/unaligned_access_speed.c
> +++ b/arch/riscv/kernel/unaligned_access_speed.c
> @@ -367,10 +367,12 @@ static void check_vector_unaligned_access(struct work_struct *work __always_unus
>  
>  static int riscv_online_cpu_vec(unsigned int cpu)
>  {
> -	if (!has_vector())
> +	if (!has_vector()) {
> +		per_cpu(vector_misaligned_access, cpu) = RISCV_HWPROBE_MISALIGNED_VECTOR_UNSUPPORTED;
>  		return 0;
> +	}
>  
> -	if (per_cpu(vector_misaligned_access, cpu) != RISCV_HWPROBE_MISALIGNED_VECTOR_UNSUPPORTED)
> +	if (per_cpu(vector_misaligned_access, cpu) != RISCV_HWPROBE_MISALIGNED_VECTOR_UNKNOWN)
>  		return 0;
>  
>  	check_vector_unaligned_access_emulated(NULL);

Hi Andrew,

Wouldn't it be easier just not to register the hotplug callback in case
!has_vector() ? In which case just set all possible cpus
vector_misaligned_access to RISCV_HWPROBE_MISALIGNED_VECTOR_UNSUPPORTED
at startup.

Thanks,

Clément