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

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Message-ID: <20250207-f0e7e2b868ef3e9f2a174f29@orel>
Date: Fri, 7 Feb 2025 18:08:22 +0100
From: Andrew Jones <ajones@...tanamicro.com>
To: Clément Léger <cleger@...osinc.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 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.

Thanks,
drew