[PATCH v3 0/4] cpufreq: CPPC: Preserve OSPM-set registers across hotplug and unload

[Sumit Gupta <sumitg@nvidia.com>]

This series keeps the CPPC cpufreq policy alive across CPU hotplug and
preserves the OSPM-set CPPC registers (Energy Performance Preference,
Autonomous Activity Window, Autonomous Selection) set via sysfs or the
autonomous boot parameter.

Without online()/offline() callbacks, the core tears a policy down when
its last CPU goes offline and rebuilds it on the way back, re-reading the
CPPC capabilities each time. The values written to these registers can
be lost:

 - Across CPU hotplug or suspend/resume: the platform may reset them
   while the CPU is offline.
 - On driver unload: the driver-written value is left in the register
   instead of returning to its pre-driver state.

Handle these with:
 - Patch 1: adds online()/offline() callbacks so the core keeps the policy
   alive across CPU hotplug instead of tearing it down and rebuilding it.
 - Patch 2: makes the autonomous selection register helpers take a u64.
 - Patch 3: adds a table-driven mechanism that captures each register's
   firmware value, restores it when the policy goes down, and reapplies
   the OSPM-set value when the policy comes back online.
 - Patch 4: extends the same save/restore to system suspend/resume.

v2[2] -> v3:
 - Patch 1: online() now re-establishes the desired/min/max tuple.
 - Patch 2: make cppc_get/set_auto_sel() take a u64 arg.
 - Patch 3: skip restoring/reapplying a reg whose value couldn't be read.
 - Patch 3: split save_req_and_restore_firmware_regs() so patch 4 can
   reuse save_requested_regs() for save-only suspend.
 - New patch 4: preserve the OSPM-set registers across suspend/resume.

Sumit Gupta (4):
  cpufreq: CPPC: Keep the policy across CPU hotplug
  ACPI: CPPC: Make autonomous selection helpers take a u64
  cpufreq: CPPC: Preserve OSPM-set registers across hotplug and unload
  cpufreq: CPPC: Preserve OSPM-set registers across suspend/resume

 drivers/acpi/cppc_acpi.c       |  20 +--
 drivers/cpufreq/amd-pstate.c   |   2 +-
 drivers/cpufreq/cppc_cpufreq.c | 223 ++++++++++++++++++++++++++++++++-
 include/acpi/cppc_acpi.h       |   8 +-
 4 files changed, 230 insertions(+), 23 deletions(-)

[1] v1: https://lore.kernel.org/lkml/20260623095403.3407436-1-sumitg@nvidia.com/
[2] v2: https://lore.kernel.org/lkml/20260716153820.2007095-1-sumitg@nvidia.com/

-- 
2.34.1