Re: [PATCH] ACPI: CPPC: Skip writes to unsupported performance controls

On Fri, Jul 24, 2026 at 11:40:42AM +0100, Christian Loehle wrote:
> MIN_PERF and MAX_PERF are optional CPPC controls. DESIRED_PERF is also
> optional with CPPC2 when autonomous selection is supported.
> 
> The cppc-cpufreq target callbacks populate both limits for every request
> without checking whether the controls are implemented. cppc_set_perf()
> consequently passes NULL register descriptors to cpc_write(). The writes
> fail width validation and their return values are ignored, so the failed
> access paths are repeated on every target request. An autonomous-only
> platform can take the same path for DESIRED_PERF.
> 
> Check that each performance control is supported before calling
> cpc_write().
> 
> Fixes: ea3db45ae476 ("cpufreq: cppc: Update MIN_PERF/MAX_PERF in target callbacks")
> Reviewed-by: Sumit Gupta <[email protected]>
> Signed-off-by: Christian Loehle <[email protected]>
> ---
> v2: Also added desired_perf check (Sumit)
> 
>  drivers/acpi/cppc_acpi.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
> index 1d3a94100491..53d09ca98f06 100644
> --- a/drivers/acpi/cppc_acpi.c
> +++ b/drivers/acpi/cppc_acpi.c
> @@ -1963,16 +1963,17 @@ int cppc_set_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls)
>  		cpc_desc->write_cmd_status = 0;
>  	}
>  
> -	cpc_write(cpu, desired_reg, perf_ctrls->desired_perf);
> +	if (CPC_SUPPORTED(desired_reg))
> +		cpc_write(cpu, desired_reg, perf_ctrls->desired_perf);
>  

In general, can't be set perf_ctrls->desired_perf if and only if
CPC_SUPPORTED(desired_reg) ?

I see cppc_get_perf() does that but I assume you are catering for some
other access that may happen before ?

-- 
Regards,
Sudeep