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

["Christophe Leroy (CS GROUP)" <chleroy@kernel.org>]

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@kernel.org>