[PATCH 2/2] x86/topology: Add TOPO_CPU_TYPE_LOW_POWER

[Vishal Badole]

AMD heterogeneous parts report a third core type via CPUID
Fn0x80000026 EBX[31:28] (Extended CPU Topology, Core Type):

  0 - Performance
  1 - Efficiency
  2 - Low Power

get_topology_cpu_type() only translates the first two, so on parts
that ship low-power cores the third type falls through to
TOPO_CPU_TYPE_UNKNOWN. That has two visible effects:

  - /sys/kernel/debug/x86/topo/cpus/* reports cpu_type "unknown" via
    get_topology_cpu_type_name().

  - amd_get_boost_ratio_numerator() hits the default arm of its
    x86_topology_cpu_type switch and uses the
    CPPC_HIGHEST_PERF_PREFCORE fallback instead of scaling by
    amd_get_highest_perf() as efficiency cores do.

Add TOPO_CPU_TYPE_LOW_POWER, translate AMD_CPU_TYPE_LOW_POWER to it
in get_topology_cpu_type(), and expose a "low_power" name via
get_topology_cpu_type_name().

In amd_get_boost_ratio_numerator(), share the efficiency-core arm of
the switch with the new type so low-power cores scale by
amd_get_highest_perf() rather than the performance-core ceiling. The
new case sits under the existing
cpu_feature_enabled(X86_FEATURE_AMD_HTR_CORES) gate and therefore
applies to every HTR_CORES-capable AMD/Hygon part that reports core
type 2.

Signed-off-by: Vishal Badole <Vishal.Badole@xxxxxxx>
---
 arch/x86/include/asm/topology.h       | 1 +
 arch/x86/kernel/acpi/cppc.c           | 3 ++-
 arch/x86/kernel/cpu/topology_common.c | 3 +++
 3 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/topology.h b/arch/x86/include/asm/topology.h
index 9658b5676ce6..1e65a6ea5de4 100644
--- a/arch/x86/include/asm/topology.h
+++ b/arch/x86/include/asm/topology.h
@@ -117,6 +117,7 @@ enum x86_topology_domains {
 enum x86_topology_cpu_type {
 	TOPO_CPU_TYPE_PERFORMANCE,
 	TOPO_CPU_TYPE_EFFICIENCY,
+	TOPO_CPU_TYPE_LOW_POWER,
 	TOPO_CPU_TYPE_UNKNOWN,
 };
 
diff --git a/arch/x86/kernel/acpi/cppc.c b/arch/x86/kernel/acpi/cppc.c
index d7c8ef1e354d..df2c7579309c 100644
--- a/arch/x86/kernel/acpi/cppc.c
+++ b/arch/x86/kernel/acpi/cppc.c
@@ -281,8 +281,9 @@ int amd_get_boost_ratio_numerator(unsigned int cpu, u64 *numerator)
 			/* use the max scale for performance cores */
 			*numerator = CPPC_HIGHEST_PERF_PERFORMANCE;
 			return 0;
+		case TOPO_CPU_TYPE_LOW_POWER:
 		case TOPO_CPU_TYPE_EFFICIENCY:
-			/* use the highest perf value for efficiency cores */
+			/* use the highest perf value for efficiency and low-power cores */
 			ret = amd_get_highest_perf(cpu, &tmp);
 			if (ret)
 				return ret;
diff --git a/arch/x86/kernel/cpu/topology_common.c b/arch/x86/kernel/cpu/topology_common.c
index e1cc25a115ca..8c8267c812e0 100644
--- a/arch/x86/kernel/cpu/topology_common.c
+++ b/arch/x86/kernel/cpu/topology_common.c
@@ -44,6 +44,7 @@ enum x86_topology_cpu_type get_topology_cpu_type(struct cpuinfo_x86 *c)
 		switch (c->topo.amd_type) {
 		case AMD_CPU_TYPE_PERFORMANCE:	return TOPO_CPU_TYPE_PERFORMANCE;
 		case AMD_CPU_TYPE_EFFICIENCY:	return TOPO_CPU_TYPE_EFFICIENCY;
+		case AMD_CPU_TYPE_LOW_POWER:	return TOPO_CPU_TYPE_LOW_POWER;
 		}
 	}
 
@@ -57,6 +58,8 @@ const char *get_topology_cpu_type_name(struct cpuinfo_x86 *c)
 		return "performance";
 	case TOPO_CPU_TYPE_EFFICIENCY:
 		return "efficiency";
+	case TOPO_CPU_TYPE_LOW_POWER:
+		return "low_power";
 	default:
 		return "unknown";
 	}
-- 
2.34.1