linux-kernel - Re: [External] Re: [PATCH v3 1/1] arch_topology: move parse_acpi

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Message-ID: <CAEEQ3w=4aKS=p=+q4iC42Va+dMVm017R0Surxff+4R+4RjkgAg@mail.gmail.com>
Date: Mon, 22 Sep 2025 19:04:05 +0800
From: yunhui cui <cuiyunhui@...edance.com>
To: Sudeep Holla <sudeep.holla@....com>
Cc: catalin.marinas@....com, will@...nel.org, gregkh@...uxfoundation.org, 
	rafael@...nel.org, dakr@...nel.org, beata.michalska@....com, 
	ptsm@...ux.microsoft.com, sumitg@...dia.com, yangyicong@...ilicon.com, 
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [External] Re: [PATCH v3 1/1] arch_topology: move
 parse_acpi_topology() to common code

Hi Sudeep,

On Mon, Sep 22, 2025 at 5:01 PM Sudeep Holla <sudeep.holla@....com> wrote:
>
> On Mon, Sep 22, 2025 at 10:18:57AM +0800, yunhui cui wrote:
> > Hi Sudeep,
> >
> > On Fri, Sep 19, 2025 at 10:05 PM Sudeep Holla <sudeep.holla@....com> wrote:
>
> [...]
>
> > >
> > > Just thinking if it makes sense keep acpi_cpu_is_threaded generic without
> > > the need for weak definition.
> > >
> > > Additional note: not sure why you haven't moved this under CONFIG_ARM64/RISCV as
> > > done with other code.
> > >
> > > bool __init acpi_cpu_is_threaded(int cpu)
> > > {
> > >         int is_threaded = acpi_pptt_cpu_is_thread(cpu);
> > >
> > >         /*
> > >          * if the PPTT doesn't have thread information, check for architecture
> > >          * specific fallback if available
> > >          */
> > >         if (is_threaded < 0)
> > >                 is_threaded = arch_cpu_is_threaded();
> > >
> > >         return !!is_threaded;
> > > }
> > >
> > > Then you can just have the define in
> > >
> > > #define arch_cpu_is_threaded() (read_cpuid_mpidr() & MPIDR_MT_BITMASK)
> > >
> > > in arch/arm64/include/asm/topology.h
> > >
> > > and
> > >
> > > +#ifndef arch_cpu_is_threaded
> > > +#define arch_cpu_is_threaded           (0)
> > > +#endif
> > >
> > > in include/linux/arch_topology.h
> > >
> > > Thoughts ?
> >
> > If placed in include/linux/arch_topology.h, there is a possibility
> > that "arch_cpu_is_threaded" will be redefined.
> >
>
> Why is that a problem ? We want arch to override the default definition
> if and when required.

Because include/linux/topology.h first includes linux/arch_topology.h,
and then includes asm/topology.h, a warning will be generated during
compilation:

In file included from ./include/linux/topology.h:37,
                 from ./include/linux/gfp.h:8,
                 from ./include/linux/xarray.h:16,
                 from ./include/linux/list_lru.h:14,
                 from ./include/linux/fs.h:14,
                 from kernel/events/core.c:11:
./arch/arm64/include/asm/topology.h:39: warning:
"arch_cpu_is_threaded" redefined
   39 | #define arch_cpu_is_threaded() (read_cpuid_mpidr() & MPIDR_MT_BITMASK)
      |
In file included from ./include/linux/topology.h:30:
./include/linux/arch_topology.h:94: note: this is the location of the
previous definition
   94 | #define arch_cpu_is_threaded()  (0)

Unless #undef arch_cpu_is_threaded is used in arch/arm64/include/asm/topology.h,

So it's better to place
#ifndef arch_cpu_is_threaded
#define arch_cpu_is_threaded (0)
#endif
in include/asm-generic/topology.h.

>
> --
> Regards,
> Sudeep

Thanks,
Yunhui