[RFC PATCH v4 0/8] SRF: Fix offline CPU preventing pc6 entry

[Patryk Wlazlyn <patryk.wlazlyn@linux.intel.com>]

Sending an interim RFC patch. Rebased on top of Rafael's patches and
applied modified patch/suggestion from Gautham.

Please tell me what you think. Is this approach in general is
acceptable?

When playing dead we have now the preference ordered:
 1. Idle driver.
      - acpi_idle can now do FFH and calls mwait_play_dead_with_hint,
        but we disable the handlers on AMD, because AMD doesn't want to
        use mwait for play_dead.
      - intel_idle have a handler for SRF. Intel platforms fallback to
        cpuid leaf 0x5 on other platforms.
 2. Old mwait_play_dead() based on cpuid leaf 0x5.
 3. hlt_play_dead().


Changes since v3:
 * Reworded commit messages authored by me as advised by Dave.
   Expanded the context about the mwait_play_dead code, hint computation
   and what is a problem we observe and the patch addresses.
 * Different play_dead methods are called now one after the other,
   because they only return on success.

Patryk Wlazlyn (5):
  x86/smp: Allow calling mwait_play_dead with arbitrary hint
  x86/smp native_play_dead: Prefer cpuidle_play_dead() over
    mwait_play_dead()
  intel_idle: Provide enter_dead() handler for SRF
  acpi_idle: Add FFH cstate handling
  acpi_idle: Disallow play_dead with FFH cstate on AMD platforms

Rafael J. Wysocki (3):
  cpuidle: Do not return from cpuidle_play_dead() on callback failures
  cpuidle: Change :enter_dead() driver callback return type to void
  ACPI: processor_idle: Use acpi_idle_play_dead() for all C-states

 arch/x86/include/asm/cpufeatures.h |  1 +
 arch/x86/include/asm/smp.h         |  3 +
 arch/x86/kernel/acpi/cstate.c      |  9 +++
 arch/x86/kernel/smpboot.c          | 91 ++++++++++++++++--------------
 drivers/acpi/processor_idle.c      | 23 ++++----
 drivers/cpuidle/cpuidle.c          | 10 +++-
 drivers/idle/intel_idle.c          | 15 +++++
 include/acpi/processor.h           |  5 ++
 include/linux/cpuidle.h            |  2 +-
 9 files changed, 103 insertions(+), 56 deletions(-)

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2.47.0