linux-kernel - Re: [PATCH] riscv: cacheinfo: init cache levels via fetch_cache

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Message-ID: <ffb83627-bd28-4bf9-8051-57dfca407f87@ghiti.fr>
Date: Fri, 1 Aug 2025 13:45:58 +0200
From: Alexandre Ghiti <alex@...ti.fr>
To: liu.xuemei1@....com.cn, paul.walmsley@...ive.com
Cc: palmer@...belt.com, aou@...s.berkeley.edu, spersvold@...il.com,
 sudeep.holla@....com, mikisabate@...il.com, robh@...nel.org,
 linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] riscv: cacheinfo: init cache levels via fetch_cache_info
 when SMP disabled

Hi Jessica,

On 8/1/25 03:32, liu.xuemei1@....com.cn wrote:
>
> On 7/31/25 21:29, alex@...ti.fr wrote:
>
> > > From: Jessica Liu <liu.xuemei1@....com.cn>
>
> > >
>
> > > As described in commit 1845d381f280 ("riscv: cacheinfo: Add back
>
> > > init_cache_level() function"), when CONFIG_SMP is undefined, the cache
>
> > > hierarchy detection needs to be performed through the 
> init_cache_level(),
>
> > > whereas when CONFIG_SMP is defined, this detection is handled 
> during the
>
> > > init_cpu_topology() process.
>
> > >
>
> > > Furthermore, while commit 66381d36771e ("RISC-V: Select ACPI PPTT 
> drivers")
>
> > > enables cache information retrieval through the ACPI PPTT table, the
>
> > > init_of_cache_level() called within init_cache_level() cannot 
> support cache
>
> > > hierarchy detection through ACPI PPTT. Therefore, when CONFIG_SMP is
>
> > > undefined, we directly invoke the fetch_cache_info function to 
> initialize
>
> > > the cache levels.
>
> > >
>
> > > Signed-off-by: Jessica Liu <liu.xuemei1@....com.cn>
>
> > > ---
>
> > >   arch/riscv/kernel/cacheinfo.c | 6 +++++-
>
> > >   1 file changed, 5 insertions(+), 1 deletion(-)
>
> > >
>
> > > diff --git a/arch/riscv/kernel/cacheinfo.c 
> b/arch/riscv/kernel/cacheinfo.c
>
> > > index 26b085dbdd07..f81ca963d177 100644
>
> > > --- a/arch/riscv/kernel/cacheinfo.c
>
> > > +++ b/arch/riscv/kernel/cacheinfo.c
>
> > > @@ -73,7 +73,11 @@ static void ci_leaf_init(struct cacheinfo 
> *this_leaf,
>
> > >
>
> > >   int init_cache_level(unsigned int cpu)
>
> > >   {
>
> > > -    return init_of_cache_level(cpu);
>
> > > +#ifdef CONFIG_SMP
>
> > > +    return 0;
>
> > > +#endif
>
> > > +
>
> > > +    return fetch_cache_info(cpu);
>
> > >   }
>
> > >
>
> > >   int populate_cache_leaves(unsigned int cpu)
>
> >
>
> >
>
> > Is the current behaviour wrong or just redundant? If wrong, I'll add a
>
> > Fixes tag to backport, otherwise I won't.
>
> >
>
> > Thanks,
>
> >
>
> > Alex
>
>
> Hi Alex,
>
>
> The current behavior is actually wrong when using ACPI on !CONFIG_SMP
>
> systems. The original init_of_cache_level() cannot detect cache hierarchy
>
> through ACPI PPTT table, which means cache information would be missing
>
> in this configuration.
>
>
> The patch fixes this by directly calling fetch_cache_info() when
>
> CONFIG_SMP is undefined, which properly handles both DT and ACPI cases.
>
>
> So yes, it would be appropriate to add a Fixes tag. The commit being
>
> fixed is 1845d381f280 ("riscv: cacheinfo: Add back init_cache_level() 
> function").
>
>
> Please let me know if you need any additional information.
>

I'm about to send my first PR for 6.17 so I'll delay merging this one 
for the first rc.

Thanks for the explanation,

Alex


>
> Best regards,
>
> Jessica
>
>
>
>
>
>