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

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Message-ID: <fdabae33-a1df-41f7-9e1f-9973f252599a@rivosinc.com>
Date: Fri, 7 Feb 2025 18:43:26 +0100
From: Clément Léger <cleger@...osinc.com>
To: Andrew Jones <ajones@...tanamicro.com>
Cc: linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
 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 18:08, Andrew Jones wrote:
> On Fri, Feb 07, 2025 at 05:47:28PM +0100, Clément Léger wrote:
>>
>>
>> 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.
> 
> We could do that, but I have another use for the hotplug callback that
> you'll see near the end of the series.

Ok, I saw patch 7/9.

BTW, what happened to patch 8 ? I thought it was in my spam but even
lore.kernel.org does not have it:
https://lore.kernel.org/linux-riscv/20250207161939.46139-11-ajones@ventanamicro.com/T/#t

Thanks,

Clément

> 
> Thanks,
> drew