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

Sumit Gupta
2025-12-23T12:15:23Z

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);
+ if (!cpu_policy)
+ return -ENODEV;
+
+ cpu_data = cpu_policy->driver_data;
+ caps = &cpu_data->perf_caps;
+
+ 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);
+ }
+
+ cpufreq_cpu_put(cpu_policy);
return 0;
}

--
2.34.1