cpufreq / CPPC: Initialize policy->min to lowest nonlinear performance

Description of Lowest Perfomance in ACPI 6.1 specification states:
"Lowest Performance is the absolute lowest performance level of
the platform. Selecting a performance level lower than the lowest
nonlinear performance level may actually cause an efficiency penalty,
but should reduce the instantaneous power consumption of the processor.
In traditional terms, this represents the T-state range of performance
levels."

Set the default value of policy->min to Lowest Nonlinear Performance
to avoid any potential efficiency penalty.

Signed-off-by: Prashanth Prakash <pprakash@codeaurora.org>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Acked-by: Alexey Klimov <alexey.klimov@arm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

1 files changed, 16 insertions, 3 deletions

diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
index e82bb3c30b92..10be285c9055 100644
--- a/drivers/cpufreq/cppc_cpufreq.c
+++ b/drivers/cpufreq/cppc_cpufreq.c
@@ -144,10 +144,23 @@ static int cppc_cpufreq_cpu_init(struct cpufreq_policy *policy)
 
         cppc_dmi_max_khz = cppc_get_dmi_max_khz();
 
-        policy->min = cpu->perf_caps.lowest_perf * cppc_dmi_max_khz / cpu->perf_caps.highest_perf;
+        /*
+         * Set min to lowest nonlinear perf to avoid any efficiency penalty (see
+         * Section 8.4.7.1.1.5 of ACPI 6.1 spec)
+         */
+        policy->min = cpu->perf_caps.lowest_nonlinear_perf * cppc_dmi_max_khz /
+                cpu->perf_caps.highest_perf;
         policy->max = cppc_dmi_max_khz;
-        policy->cpuinfo.min_freq = policy->min;
-        policy->cpuinfo.max_freq = policy->max;
+
+        /*
+         * Set cpuinfo.min_freq to Lowest to make the full range of performance
+         * available if userspace wants to use any perf between lowest & lowest
+         * nonlinear perf
+         */
+        policy->cpuinfo.min_freq = cpu->perf_caps.lowest_perf * cppc_dmi_max_khz /
+                cpu->perf_caps.highest_perf;
+        policy->cpuinfo.max_freq = cppc_dmi_max_khz;
+
         policy->cpuinfo.transition_latency = cppc_get_transition_latency(cpu_num);
         policy->shared_type = cpu->shared_type;