cpufreq: intel_pstate: Fix ->set_policy() interface for no_turbo

commit 983e600e upstream.

When turbo is disabled, the ->set_policy() interface is broken.

For example, when turbo is disabled and cpuinfo.max = 2900000 (full
max turbo frequency), setting the limits results in frequency less
than the requested one:
Set 1000000 KHz results in 0700000 KHz
Set 1500000 KHz results in 1100000 KHz
Set 2000000 KHz results in  1500000 KHz

This is because the limits->max_perf fraction is calculated using
the max turbo frequency as the reference, but when the max P-State is
capped in intel_pstate_get_min_max(), the reference is not the max
turbo P-State. This results in reducing max P-State.

One option is to always use max turbo as reference for calculating
limits. But this will not be correct. By definition the intel_pstate
sysfs limits, shows percentage of available performance. So when
BIOS has disabled turbo, the available performance is max non turbo.
So the max_perf_pct should still show 100%.
Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
[ rjw : Subject & changelog, rewrite in fewer lines of code ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
[bwh: Backported to 3.16:
 - limits is a perf_limits structure, not a pointer to it
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/cpufreq/intel_pstate.c

@@ -877,8 +877,11 @@ static int intel_pstate_cpu_init(struct cpufreq_policy *policy)
 
 	/* cpuinfo and default policy values */
 	policy->cpuinfo.min_freq = cpu->pstate.min_pstate * cpu->pstate.scaling;
-	policy->cpuinfo.max_freq =
-		cpu->pstate.turbo_pstate * cpu->pstate.scaling;
+	update_turbo_state();
+	policy->cpuinfo.max_freq = limits.turbo_disabled ?
+			cpu->pstate.max_pstate : cpu->pstate.turbo_pstate;
+	policy->cpuinfo.max_freq *= cpu->pstate.scaling;
+
 	policy->cpuinfo.transition_latency = CPUFREQ_ETERNAL;
 	cpumask_set_cpu(policy->cpu, policy->cpus);