Re: [PATCH] cpufreq/amd-pstate: Do not fail init when auto_sel cannot be written

[Wentao Guan]

Hi,

> On 9/18/2026 10:12 AM, Wentao Guan wrote:
> > Since commit 9dfd13f80c85 ("cpufreq/amd-pstate: Toggle auto_sel in active
> > mode on shared memory systems"), shmem_init_perf() programs
> > AUTONOMOUS_SELECTION_ENABLE unconditionally, including in active mode.
> >
> > On platforms implementing CPPC v2 and below, _CPC reports Autonomous
> > Selection Enable as a plain integer rather than as a register descriptor.
> > Such a field is a read-only capability flag: cppc_get_reg_val() reads it
> > back successfully (the firmware reports it as enabled), while
> > cppc_set_reg_val() rejects the write with -EOPNOTSUPP because the entry is
> > not an ACPI_TYPE_BUFFER.
> 
> Ah! So it is one of those platforms that fall into:
> 
>     Platforms that exclusively support Autonomous Selection must populate
>     this field as an Integer with a value of 1.
> 
> as per the ACPI spec.
> 
> >
> > shmem_init_perf() propagates that error, so every amd_pstate_epp_cpu_init()
> > fails, cpufreq_register_driver() ends up with an empty policy list and
> > returns -ENODEV, and amd-pstate refuses to load at all:
> >
> >   amd_pstate: failed to set auto_sel, ret: -95
> >   amd_pstate: Failed to initialize CPU 0: -95
> >   ...
> >   amd_pstate: failed to register with return -19
> >
> > Failing to write auto_sel is not fatal: the register is either already
> > enabled, as reported by the cppc_get_auto_sel() call right above, or not
> > writable at all, and active mode worked in both cases before the offending
> > commit.  Downgrade the failure to a warning and let initialization
> > continue, matching how the cppc_get_auto_sel() failure is handled.
> 
> Can't we just skip cppc_set_auto_sel() if the auto_sel is already at
> the desired value? Something like:
> 
>   (Completely untested)
> 
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index d4ff8b228f86..ed540da818ef 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -524,6 +524,9 @@ static int shmem_init_perf(struct amd_cpudata *cpudata)
>  		return 0;
>  	}
> 
> +	if ((cppc_state != AMD_PSTATE_PASSIVE) == auto_sel)
> +		return 0;
> +
>  	ret = cppc_set_auto_sel(cpudata->cpu,
>  			(cppc_state == AMD_PSTATE_PASSIVE) ? 0 : 1);
> 
> ---
> 
> That way we fail for passive mode switch which will operate under
> incorrectly assumptions since these platform only supports autonomous
> modes.

> Thoughts?

Thanks for your review, full agree with your suggested patch.
I will send v2 after be tested later.

BRs
Wentao Guan