[PATCH v2 0/3] x86/topology: Add support for Low Power cpu_type

[Vishal Badole <Vishal.Badole@amd.com>]

This series extends the x86 topology cpu_type classification to support
a Low Power core type, in addition to the existing Performance and
Efficiency types.

AMD heterogeneous parts report the core type via CPUID Fn0x80000026
EBX[31:28] (Extended CPU Topology, Core Type). Value 2 identifies a
low-power core. Distinguishing it from a regular efficiency core
matters for:

  - user space exposure via /sys/kernel/debug/x86/topo/cpus/*, which
    today reports cpu_type "unknown" for low-power cores

  - amd_get_boost_ratio_numerator(): on every
    X86_FEATURE_AMD_HTR_CORES-capable AMD/Hygon part, low-power cores
    must scale by amd_get_highest_perf() rather than the fixed
    CPPC_HIGHEST_PERF_PERFORMANCE ceiling, matching the existing
    efficiency-core path

During the v1 review, Sashiko flagged a pre-existing issue in how
x86_match_cpu() handles vendor CPU types. v2 therefore starts with a
preparatory patch from Borislav that switches matching to the kernel's
vendor-agnostic TOPO_CPU_TYPE_* enum; see its commit message for
details. The Low Power support is then added on top.

The series is structured as:

  1/3 Map the vendor (Intel/AMD) hardware core type to the
      vendor-agnostic enum x86_topology_cpu_type at enumeration and
      match against it. See the patch's commit message for details.

  2/3 Replace the bare 0/1 in get_topology_cpu_type() with named
      enum amd_cpu_type constants, mirroring the existing Intel side.
      No functional change.

  3/3 Add TOPO_CPU_TYPE_LOW_POWER, wire it through
      get_topology_cpu_type(), get_topology_cpu_type_name() and the
      switch in amd_get_boost_ratio_numerator() so allmodconfig builds
      cleanly under -Werror=switch.

Changes in v2:
  - New preparatory patch 1/3 from Borislav Petkov switching
    x86_match_cpu() to the vendor-agnostic TOPO_CPU_TYPE_* enum; see
    its commit message for the rationale. (Thomas Gleixner,
    Borislav Petkov)
  - No change to the Low Power translation logic itself; patches 2/3
    and 3/3 are the v1 patches rebased on top of the new 1/3.

v1: https://lore.kernel.org/all/20260629094349.533301-1-Vishal.Badole@amd.com

Borislav Petkov (AMD) (1):
  x86/topo: Map vendor CPU types to generic Linux such types

Vishal Badole (2):
  x86/topology: Name the AMD core-type values
  x86/topology: Add TOPO_CPU_TYPE_LOW_POWER

 arch/x86/include/asm/processor.h      | 19 +++++++++++++----
 arch/x86/include/asm/topology.h       |  9 ++++----
 arch/x86/kernel/acpi/cppc.c           |  7 ++++---
 arch/x86/kernel/cpu/match.c           | 30 +--------------------------
 arch/x86/kernel/cpu/topology.h        |  1 +
 arch/x86/kernel/cpu/topology_amd.c    |  6 ++++--
 arch/x86/kernel/cpu/topology_common.c | 15 ++++++++++----
 7 files changed, 40 insertions(+), 47 deletions(-)

-- 
2.34.1