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) <chle...@kernel.org>