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

[zhenglifeng (A)]

On 7/24/2026 5:56 AM, Christian Loehle wrote:
> MIN_PERF and MAX_PERF are optional CPPC controls. The cppc-cpufreq
> target callbacks nevertheless populate both values for every request
> without checking whether the controls are implemented.
> 
> cppc_set_perf() consequently passes a NULL register descriptor to
> cpc_write(). The write fails width validation and its return value is
> ignored, so the failed access path is repeated on every target request.
> 
> Check that each optional limit control is supported before calling
> cpc_write().
> 
> Fixes: ea3db45ae476 ("cpufreq: cppc: Update MIN_PERF/MAX_PERF in target callbacks")
> Signed-off-by: Christian Loehle <christian.loehle@xxxxxxx>
> ---
>  drivers/acpi/cppc_acpi.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
> index 1d3a94100491..7bac6d5da24b 100644
> --- a/drivers/acpi/cppc_acpi.c
> +++ b/drivers/acpi/cppc_acpi.c
> @@ -1970,9 +1970,9 @@ int cppc_set_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls)
>  	 * value to min and max perf, but they don't mean to set the zero value,
>  	 * they just don't want to write to those registers.
>  	 */
> -	if (perf_ctrls->min_perf)
> +	if (perf_ctrls->min_perf && CPC_SUPPORTED(min_perf_reg))
>  		cpc_write(cpu, min_perf_reg, perf_ctrls->min_perf);
> -	if (perf_ctrls->max_perf)
> +	if (perf_ctrls->max_perf && CPC_SUPPORTED(max_perf_reg))
>  		cpc_write(cpu, max_perf_reg, perf_ctrls->max_perf);
>  
>  	if (CPC_IN_PCC(desired_reg) || CPC_IN_PCC(min_perf_reg) || CPC_IN_PCC(max_perf_reg))

LGTM.

Reviewed-by: Lifeng Zheng <zhenglifeng1@xxxxxxxxxx>