cpufreq: intel_pstate: Add base_frequency attribute

Expose base_frequency to user space via cpufreq sysfs when HWP is in
use.

This HWP base frequency is read from the ACPI _CPC object if present,
or from the HWP Capabilities MSR otherwise.

On the majority of the HWP platforms the _CPC object will point to
the HWP Capabilities MSR using the "Functional Fixed Hardware"
address space type.  The address space type also can simply be
ACPI_TYPE_INTEGER, however, in which case the platform firmware
can set its value at the initialization time based on the system
constraints.

Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
[ rjw: Changelog ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/cpufreq/intel_pstate.c

@@ -373,10 +373,28 @@ static void intel_pstate_set_itmt_prio(int cpu)
 		}
 	}
 }
+
+static int intel_pstate_get_cppc_guranteed(int cpu)
+{
+	struct cppc_perf_caps cppc_perf;
+	int ret;
+
+	ret = cppc_get_perf_caps(cpu, &cppc_perf);
+	if (ret)
+		return ret;
+
+	return cppc_perf.guaranteed_perf;
+}
+
 #else
 static void intel_pstate_set_itmt_prio(int cpu)
 {
 }
+
+static int intel_pstate_get_cppc_guranteed(int cpu)
+{
+	return -ENOTSUPP;
+}
 #endif
 
 static void intel_pstate_init_acpi_perf_limits(struct cpufreq_policy *policy)
@@ -699,9 +717,29 @@ static ssize_t show_energy_performance_preference(
 
 cpufreq_freq_attr_rw(energy_performance_preference);
 
+static ssize_t show_base_frequency(struct cpufreq_policy *policy, char *buf)
+{
+	struct cpudata *cpu;
+	u64 cap;
+	int ratio;
+
+	ratio = intel_pstate_get_cppc_guranteed(policy->cpu);
+	if (ratio <= 0) {
+		rdmsrl_on_cpu(policy->cpu, MSR_HWP_CAPABILITIES, &cap);
+		ratio = HWP_GUARANTEED_PERF(cap);
+	}
+
+	cpu = all_cpu_data[policy->cpu];
+
+	return sprintf(buf, "%d\n", ratio * cpu->pstate.scaling);
+}
+
+cpufreq_freq_attr_ro(base_frequency);
+
 static struct freq_attr *hwp_cpufreq_attrs[] = {
 	&energy_performance_preference,
 	&energy_performance_available_preferences,
+	&base_frequency,
 	NULL,
 };