Re: [PATCH v2 1/2] powerpc: Introduce POWER10_DD1 feature

[Ravi Bangoria <ravi.bangoria@linux.ibm.com>]

>>>> +static void __init fixup_cpu_features(void)
>>>> +{
>>>> +       unsigned long version = mfspr(SPRN_PVR);
>>>> +
>>>> +       if ((version & 0xffffffff) == 0x00800100)
>>>> +               cur_cpu_spec->cpu_features |= CPU_FTR_POWER10_DD1;
>>>> +}
>>>> +
>>> I am just wondering why this is needed here, but the same thing is not
>>> done for, say, CPU_FTR_POWER9_DD2_1?
>>
>> When we don't use DT cpu_features (PowerVM / kvm geusts), we call
>> identify_cpu() twice. First with Real PVR which sets "raw" cpu_spec
>> as cur_cpu_spec and then 2nd time with Logical PVR (0x0f...) which
>> (mostly) overwrites the cur_cpu_spec with "architected" mode cpu_spec.
>> I don't see DD version specific entries for "architected" mode in
>> cpu_specs[] for any previous processors. So I've introduced this
>> function to tweak cpu_features.
>>
>> Though, I don't know why we don't have similar thing for
>> CPU_FTR_POWER9_DD2_1. I've to check that.
>>
>>> And should we get a /* Power10 DD 1 */ added to cpu_specs[]?
>>
>> IIUC, we don't need such entry. For PowerVM / kvm guests, we overwrite
>> cpu_spec, so /* Power10 */ "raw" entry is sufficient. And For baremetal,
>> we don't use cpu_specs[] at all.
> I think even for powernv, using dt features can be disabled by the
> cmdline with dt_cpu_ftrs=off, then cpu_specs[] will then be used.

Ok... with dt_cpu_ftrs=off, we seem to be using raw mode cpu_specs[] entry on
baremetal. So yeah, I'll add /* Power10 DD1 */ raw mode entry into cpu_specs[].
Thanks for pointing it out.

-Ravi