[PATCH V3 2/2] cpufreq: intel_pstate: Implement ->resolve_freq()

[Viresh Kumar]

Intel pstate driver exposes min_perf_pct and max_perf_pct sysfs files,
which can be used to force a limit on the min/max P state of the driver.
Though these files eventually control the min/max frequencies that the
CPUs will run at, they don't make a change to policy->min/max values.

When the values of these files are changed (in passive mode of the
driver), it leads to calling ->limits() callback of the cpufreq
governors, like schedutil. On a call to it the governors shall
forcefully update the frequency to come within the limits. For getting
the value within limits, the schedutil governor calls
cpufreq_driver_resolve_freq(), which eventually tries to call
->resolve_freq() callback for this driver. Since the callback isn't
present, the schedutil governor fails to get the target freq within
limit and sometimes aborts the update believing that the frequency is
already set to the target value.

This patch implements the resolve_freq() callback, so the correct target
frequency can be returned by the driver and the schedutil governor gets
the frequency within limits immediately.

Fixes: ecd288429126 ("cpufreq: schedutil: Don't set next_freq to UINT_MAX")
Cc: v4.18+ <stable@xxxxxxxxxxxxxxx> # v4.18+
Reported-by: Doug Smythies <doug.smythies@xxxxxxxxx>
Signed-off-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
---
V3:
- This was earlier posted as a diff to an email reply and is getting
  sent for the first time only as a proper patch.

 drivers/cpufreq/intel_pstate.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
index cc27d4c59dca..2d84361fbebc 100644
--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -2314,6 +2314,18 @@ static int intel_cpufreq_target(struct cpufreq_policy *policy,
 	return 0;
 }
 
+static unsigned int intel_cpufreq_resolve_freq(struct cpufreq_policy *policy,
+					       unsigned int target_freq)
+{
+	struct cpudata *cpu = all_cpu_data[policy->cpu];
+	int target_pstate;
+
+	target_pstate = DIV_ROUND_UP(target_freq, cpu->pstate.scaling);
+	target_pstate = intel_pstate_prepare_request(cpu, target_pstate);
+
+	return target_pstate * cpu->pstate.scaling;
+}
+
 static unsigned int intel_cpufreq_fast_switch(struct cpufreq_policy *policy,
 					      unsigned int target_freq)
 {
@@ -2350,6 +2362,7 @@ static struct cpufreq_driver intel_cpufreq = {
 	.verify		= intel_cpufreq_verify_policy,
 	.target		= intel_cpufreq_target,
 	.fast_switch	= intel_cpufreq_fast_switch,
+	.resolve_freq	= intel_cpufreq_resolve_freq,
 	.init		= intel_cpufreq_cpu_init,
 	.exit		= intel_pstate_cpu_exit,
 	.stop_cpu	= intel_cpufreq_stop_cpu,
-- 
2.21.0.rc0.269.g1a574e7a288b