Re: [PATCH] powerpc/dt_cpu_ftrs: Set CPU_FTR_P11_PVR for Power11 and later processors

[Christophe Leroy (CS GROUP)]

Le 25/06/2026 à 15:14, Amit Machhiwal a écrit :
> Hi Christophe,
>
> <snip>
>
> > > > diff --git a/arch/powerpc/kernel/dt_cpu_ftrs.c b/arch/powerpc/kernel/dt_cpu_ftrs.c
> > > > index 3af6c06af02f..e5853daa6a48 100644
> > > > --- a/arch/powerpc/kernel/dt_cpu_ftrs.c
> > > > +++ b/arch/powerpc/kernel/dt_cpu_ftrs.c
> > > > @@ -704,6 +704,15 @@ static void __init cpufeatures_setup_start(u32 isa)
> > > >    	if (isa >= ISA_V3_1) {
> > > >    		cur_cpu_spec->cpu_features |= CPU_FTR_ARCH_31;
> > > >    		cur_cpu_spec->cpu_user_features2 |= PPC_FEATURE2_ARCH_3_1;
> > > > +
> > > > +		/*
> > > > +		 * CPU_FTR_P11_PVR is a kernel-internal flag to identify
> > > > +		 * Power11 and later processors. While ISA v3.1 is supported
> > > > +		 * by Power10+, this flag specifically indicates Power11+
> > > > +		 * for code that needs to distinguish between P10 and P11.
> > > > +		 */
> > > > +		if (PVR_VER(mfspr(SPRN_PVR)) >= PVR_POWER11)
> > >
> > > Are we sure this test will always be correct ?
> > >
> > > For instance PVR_PA6T is higher than PVR_POWER11 allthough it is not ISA 3.1
> > >
> > > Wouldn't is be cleaner and safer to just do:
> > >
> > > 	PVR_VER(mfspr(SPRN_PVR)) == PVR_POWER11
> >
> > You're absolutely right to point out the PVR ordering concern. But PA6T
> > cannot actually reach this path because we're already gated by:
> >
> >    if (isa >= ISA_V3_1)
> >
> > and PA6T does not implement ISA v3.1.
> >
> > My rationale for using `>= PVR_POWER11` is that `CPU_FTR_P11_PVR` is
> > intended to be included for Power11 and later processors, not just
> > Power11 itself, as it identifies a CPU feature. Using `== PVR_POWER11`
> > would mean we'd need to revisit this code for every future generation.
> >
> > This approach is consistent with existing kernel code. For example, in
> > arch/powerpc/perf/hv-gpci.c:
> >
> >    /* sysinfo interface files are only available for power10 and above platforms */
> >    if (PVR_VER(mfspr(SPRN_PVR)) >= PVR_POWER10)
> >        add_sysinfo_interface_files();
> >
> > Also, I couldn't find any current users of `PVR_PA6T` or `PVR_BE` in the
> > kernel tree, so there doesn't appear to be a present-day ISA v3.1+
> > example where the comparison would misidentify a processor.
> >
> > Please let me know your further thoughts on this.
>
> Just checking in — did my previous response address your concern, or do
> you have further comments?

That ok, no more comments.


Reviewed-by: Christophe Leroy (CS GROUP) <chleroy@xxxxxxxxxx>