Re: [PATCH v5 10/11] cpufreq: CPPC: make scaling_min/max_freq read-only when auto_sel enabled

zhenglifeng (A)
2025-12-26T03:26:51Z

On 2025/12/23 20:13, Sumit Gupta wrote:
> When autonomous selection (auto_sel) is enabled, the hardware controls
> performance within min_perf/max_perf register bounds making the
> scaling_min/max_freq effectively read-only.
>
> Enforce this by setting policy limits to min/max_perf bounds in
> cppc_verify_policy(). Users must use min_perf/max_perf sysfs interfaces
> to change performance limits in autonomous mode.
>
> Signed-off-by: Sumit Gupta <sumitg@nvidia.com>
> ---
> drivers/cpufreq/cppc_cpufreq.c | 32 +++++++++++++++++++++++++++++++-
> 1 file changed, 31 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
> index b1f570d6de34..b3da263c18b0 100644
> --- a/drivers/cpufreq/cppc_cpufreq.c
> +++ b/drivers/cpufreq/cppc_cpufreq.c
> @@ -305,7 +305,37 @@ static unsigned int cppc_cpufreq_fast_switch(struct cpufreq_policy *policy,
>
> static int cppc_verify_policy(struct cpufreq_policy_data *policy)
> {
> - cpufreq_verify_within_cpu_limits(policy);
> + unsigned int min_freq = policy->cpuinfo.min_freq;
> + unsigned int max_freq = policy->cpuinfo.max_freq;
> + struct cpufreq_policy *cpu_policy;
> + struct cppc_cpudata *cpu_data;
> + struct cppc_perf_caps *caps;
> +
> + cpu_policy = cpufreq_cpu_get(policy->cpu);

Better to use:

struct cpufreq_policy *cpu_policy __free(put_cpufreq_policy) = cpufreq_cpu_get(policy->cpu);

> + if (!cpu_policy)
> + return -ENODEV;
> +
> + cpu_data = cpu_policy->driver_data;
> + caps = &cpu_data->perf_caps;

cpu_policy, cpu_data and cpas are only used in the if branch. Just put them
in it.

> +
> + if (cpu_data->perf_ctrls.auto_sel) {
> + u32 min_perf, max_perf;
> +
> + /*
> + * Set policy limits to HW min/max_perf bounds. In autonomous
> + * mode, scaling_min/max_freq is effectively read-only.
> + */
> + min_perf = cpu_data->perf_ctrls.min_perf ?:
> + caps->lowest_nonlinear_perf;
> + max_perf = cpu_data->perf_ctrls.max_perf ?: caps->nominal_perf;
> +
> + policy->min = cppc_perf_to_khz(caps, min_perf);
> + policy->max = cppc_perf_to_khz(caps, max_perf);
> + } else {
> + cpufreq_verify_within_limits(policy, min_freq, max_freq);

Why not still using cpufreq_verify_within_cpu_limits()?

> + }
> +
> + cpufreq_cpu_put(cpu_policy);
> return 0;
> }
>