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

["zhenglifeng (A)" <zhenglifeng1@huawei.com>]

On 7/24/2026 6:40 PM, 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 <sumitg@nvidia.com>
> Signed-off-by: Christian Loehle <christian.loehle@arm.com>
> ---
> 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);
>  
>  	/*
>  	 * Only write if min_perf and max_perf not zero. Some drivers pass zero
>  	 * 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@huawei.com>

Apologize for replying to v1 before seeing v2.