Re: [PATCH v2] cpufreq: cppc: Clamp default minimum limit to lowest_nonlinear_perf

[zhenglifeng (A)]

Reviewed-by: Lifeng Zheng <zhenglifeng1@xxxxxxxxxx>

On 2/13/2026 6:06 PM, Pengjie Zhang wrote:
> The ACPI spec defines 'lowest_nonlinear_perf' as the threshold for
> linear performance scaling. Performance levels below this threshold
> are typically inefficient and should not be used by default.
> 
> Currently, the QoS minimum request is initialized to 0. This defaults
> the performance floor to the absolute "Lowest Performance" state
> instead of "lowest_nonlinear_perf", allowing the CPU to operate in
> an inefficient range unnecessarily.
> 
> Signed-off-by: Pengjie Zhang <zhangpengjie2@xxxxxxxxxx>
> ---
> Changes in v2:
>   - Renamed the patch subject to better reflect the logic change.
>   - Updated the commit log to clarify ACPI spec details.
> Link to v1:https://lore.kernel.org/all/20260116094555.2978887-1-zhangpengjie2@xxxxxxxxxx/
> ---
>  drivers/cpufreq/cppc_cpufreq.c | 18 ++++++++++++++++--
>  1 file changed, 16 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
> index 7e8042efedd1..4a3031d9fcf4 100644
> --- a/drivers/cpufreq/cppc_cpufreq.c
> +++ b/drivers/cpufreq/cppc_cpufreq.c
> @@ -333,9 +333,23 @@ static unsigned int cppc_cpufreq_fast_switch(struct cpufreq_policy *policy,
>  	return target_freq;
>  }
>  
> -static int cppc_verify_policy(struct cpufreq_policy_data *policy)
> +static int cppc_verify_policy(struct cpufreq_policy_data *policy_data)
>  {
> -	cpufreq_verify_within_cpu_limits(policy);
> +	if (policy_data->min == FREQ_QOS_MIN_DEFAULT_VALUE) {
> +		struct cpufreq_policy *policy __free(put_cpufreq_policy) =
> +					      cpufreq_cpu_get(policy_data->cpu);
> +		struct cppc_cpudata *cpu_data;
> +
> +		if (!policy)
> +			return -EINVAL;
> +
> +		cpu_data = policy->driver_data;
> +		policy_data->min = cppc_perf_to_khz(&cpu_data->perf_caps,
> +			cpu_data->perf_caps.lowest_nonlinear_perf);
> +	}
> +
> +	cpufreq_verify_within_cpu_limits(policy_data);
> +
>  	return 0;
>  }
>