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

[Sumit Gupta <sumitg@nvidia.com>]

On 24/07/26 03:26, Christian Loehle wrote:
> External email: Use caution opening links or attachments
>
>
> 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().

Looks good.

DESIRED_PERF is also optional when CPPC2 and autonomous selection are
enabled. Should its write also be guarded with CPC_SUPPORTED()?

Reviewed-by: Sumit Gupta <sumitg@nvidia.com>

>
> Fixes: ea3db45ae476 ("cpufreq: cppc: Update MIN_PERF/MAX_PERF in target callbacks")
> Signed-off-by: Christian Loehle <christian.loehle@arm.com>
> ---
>   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))
> --
> 2.34.1
>