cpufreq: intel_pstate: Fix scaling for hybrid-capable systems with disabled E-cores

Some system BIOS configuration may provide option to disable E-cores.
As part of this change, CPUID feature for hybrid (Leaf 7 sub leaf 0,
EDX[15] = 0) may not be set. But HWP performance limits will still be
using a scaling factor like any other hybrid enabled system.

The current check for applying scaling factor will fail when hybrid
CPUID feature is not set and the only way to make sure that scaling
should be applied by checking CPPC nominal frequency and nominal
performance.

First, or systems predating Alder Lake, the CPPC nominal frequency and
nominal performance are 0, which can be used to distinguish those
systems from hybrid systems with disabled E-cores.

Second, if the CPPC nominal frequency and nominal performance are
defined, which indicates the need to use a special scaling factor, and
the nominal performance value multiplied by 100 is not equal to the
nominal frequency one, use hybrid scaling factor.

This can be done for all HWP systems without additional CPU model check.
Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
[ rjw: Subject and changelog edits, removal of unneeded parens, comment
  edits ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/cpufreq/intel_pstate.c

@@ -302,6 +302,13 @@ static bool hwp_forced __read_mostly;
 
 static struct cpufreq_driver *intel_pstate_driver __read_mostly;
 
+#define HYBRID_SCALING_FACTOR	78741
+
+static inline int core_get_scaling(void)
+{
+	return 100000;
+}
+
 #ifdef CONFIG_ACPI
 static bool acpi_ppc;
 #endif
@@ -400,6 +407,26 @@ static int intel_pstate_get_cppc_guaranteed(int cpu)
 
 	return cppc_perf.nominal_perf;
 }
+
+static int intel_pstate_cppc_get_scaling(int cpu)
+{
+	struct cppc_perf_caps cppc_perf;
+	int ret;
+
+	ret = cppc_get_perf_caps(cpu, &cppc_perf);
+
+	/*
+	 * If the nominal frequency and the nominal performance are not
+	 * zero and the ratio between them is not 100, return the hybrid
+	 * scaling factor.
+	 */
+	if (!ret && cppc_perf.nominal_perf && cppc_perf.nominal_freq &&
+	    cppc_perf.nominal_perf * 100 != cppc_perf.nominal_freq)
+		return HYBRID_SCALING_FACTOR;
+
+	return core_get_scaling();
+}
+
 #else /* CONFIG_ACPI_CPPC_LIB */
 static inline void intel_pstate_set_itmt_prio(int cpu)
 {
@@ -492,6 +519,11 @@ static inline int intel_pstate_get_cppc_guaranteed(int cpu)
 {
 	return -ENOTSUPP;
 }
+
+static int intel_pstate_cppc_get_scaling(int cpu)
+{
+	return core_get_scaling();
+}
 #endif /* CONFIG_ACPI_CPPC_LIB */
 
 /**
@@ -1897,11 +1929,6 @@ static int core_get_turbo_pstate(int cpu)
 	return ret;
 }
 
-static inline int core_get_scaling(void)
-{
-	return 100000;
-}
-
 static u64 core_get_val(struct cpudata *cpudata, int pstate)
 {
 	u64 val;
@@ -1938,16 +1965,28 @@ static void hybrid_get_type(void *data)
 	*cpu_type = get_this_hybrid_cpu_type();
 }
 
-static int hybrid_get_cpu_scaling(int cpu)
+static int hwp_get_cpu_scaling(int cpu)
 {
 	u8 cpu_type = 0;
 
 	smp_call_function_single(cpu, hybrid_get_type, &cpu_type, 1);
 	/* P-cores have a smaller perf level-to-freqency scaling factor. */
 	if (cpu_type == 0x40)
-		return 78741;
+		return HYBRID_SCALING_FACTOR;
 
-	return core_get_scaling();
+	/* Use default core scaling for E-cores */
+	if (cpu_type == 0x20)
+		return core_get_scaling();
+
+	/*
+	 * If reached here, this system is either non-hybrid (like Tiger
+	 * Lake) or hybrid-capable (like Alder Lake or Raptor Lake) with
+	 * no E cores (in which case CPUID for hybrid support is 0).
+	 *
+	 * The CPPC nominal_frequency field is 0 for non-hybrid systems,
+	 * so the default core scaling will be used for them.
+	 */
+	return intel_pstate_cppc_get_scaling(cpu);
 }
 
 static void intel_pstate_set_pstate(struct cpudata *cpu, int pstate)
@@ -3395,8 +3434,7 @@ static int __init intel_pstate_init(void)
 			if (!default_driver)
 				default_driver = &intel_pstate;
 
-			if (boot_cpu_has(X86_FEATURE_HYBRID_CPU))
-				pstate_funcs.get_cpu_scaling = hybrid_get_cpu_scaling;
+			pstate_funcs.get_cpu_scaling = hwp_get_cpu_scaling;
 
 			goto hwp_cpu_matched;
 		}