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

[K Prateek Nayak]

Hello Wentao,

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?

> 
> Fixes: 9dfd13f80c85 ("cpufreq/amd-pstate: Toggle auto_sel in active mode on shared memory systems")
> Cc: stable@xxxxxxxxxxxxxxx
> Tested-by: LFRon <ronforever@xxxxxxxxxxx>
> Signed-off-by: Wentao Guan <guanwentao@xxxxxxxxxxxxx>
> ---
>  drivers/cpufreq/amd-pstate.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index 80d99ba1902c9..3657c5cccd4d8 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -538,5 +538,5 @@ static int shmem_init_perf(struct amd_cpudata *cpudata)
>         if (ret)
>                 pr_warn("failed to set auto_sel, ret: %d\n", ret);
> 
> -       return ret;
> +       return 0;
>  }

-- 
Thanks and Regards,
Prateek