Re: [PATCH v2] cpufreq/amd-pstate: Bail out early if !X86_FEATURE_HW_PSTATE

[Mario Limonciello]

On 7/20/26 00:14, K Prateek Nayak wrote:
> Hello Rong,
>
> On 7/18/2026 8:45 PM, Rong Zhang wrote:
> > When booting a VM that simulates or passes-through a relatively new CPU
> > model, these warning messages are printed to kmsg:
> >
> >      amd_pstate: The CPPC feature is supported but currently disabled by the BIOS.
> >      Please enable it if your BIOS has the CPPC option.
>
> This is message is printed from amd_cppc_supported() ...
>
> >      amd_pstate: the _CPC object is not present in SBIOS or ACPI disabled
>
> [..snip..]
>
> > diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> > index a74a4cf99d22..877b4b30ecd0 100644
> > --- a/drivers/cpufreq/amd-pstate.c
> > +++ b/drivers/cpufreq/amd-pstate.c
> > @@ -2228,6 +2228,13 @@ static int __init amd_pstate_init(void)
> >   	if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD)
> >   		return -ENODEV;
> >   
> > +	/*
> > +	 * Do not continue on the following checks and emit bogus warning
> > +	 * messages if the platform doesn't support frequency scaling at all.
> > +	 */
> > +	if (!cpu_feature_enabled(X86_FEATURE_HW_PSTATE))
> > +		return -ENODEV;
>
> ... so why add this check in amd_pstate_init()?
>
> I personally prefer having the check in amd_cppc_supported() and
> returning false from there with a pr_debug_once() saying processor does
> not support frequency scaling.

FWIW I agree with Prateek here.

> > +
> >   	/* show debug message only if CPPC is not supported */
> >   	if (!amd_cppc_supported())
> >   		return -EOPNOTSUPP;
> >
> > ---
> > base-commit: 94515f3a7d4256a5062176b7d6ed0471938cd51a
> > change-id: 1cc24037-amd-pstate-vm-d6ab4c959bd3
> >
> > Thanks,
> > Rong