[PATCH v7 0/5] cpufreq: CPPC: Preserve OSPM-set registers across hotplug and unload

[Sumit Gupta <sumitg@nvidia.com>]

This series preserves the OSPM-set CPPC registers (Energy Performance
Preference, Autonomous Activity Window, Autonomous Selection - set via
sysfs) across CPU hotplug and suspend/resume. On driver unload, it puts
back the values they had before the driver loaded.

To do this, it keeps the CPPC cpufreq policy alive across CPU hotplug.
It also orders the performance-control writes in cppc_set_perf(), so
that restoring them after a platform reset never sends an invalid
request.

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 or suspended.
 - 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: orders the Desired, MIN and MAX writes in cppc_set_perf(), so
   that the platform never sees an invalid request. Christian proposed
   it in [7], and this version adds fixes found in testing.
 - Patch 2: adds online()/offline() callbacks so the core keeps policy
   alive across CPU hotplug instead of tearing it down and rebuilding it.
 - Patch 3: makes the autonomous selection register helpers take a u64.
 - Patch 4: saves each register's firmware value at init() and each
   successful sysfs write as the requested value. offline() restores the
   firmware values, and online() reapplies the requested values.
 - Patch 5: extends the same restore and reapply to system
   suspend/resume.

v6[6] -> v7:
 - Patch 1:
   - clamp Desired into MIN and MAX instead of rejecting it. (Sashiko)
   - store_auto_select() updates its cache only on success. (Sashiko)
 - Patch 2:
   - exit() only frees the driver data. (Sashiko)
   - online() continues if enabling CPPC fails, as init() does.
 - Patch 4:
   - save the requested value on each successful sysfs write, instead
     of reading it in offline(). (Christian, Rafael [8])
   - init() fails if a firmware value cannot be read. (Christian)
   - split the auto_act_window store from perf_limited.
 - Patch 5:
   - suspend() no longer reads and saves the registers.

Christian Loehle (1):
  ACPI: CPPC: Order performance-control updates

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       | 318 +++++++++++++++-----
 drivers/cpufreq/amd-pstate.c   |   2 +-
 drivers/cpufreq/cppc_cpufreq.c | 530 ++++++++++++++++++++++++++++++---
 include/acpi/cppc_acpi.h       |   9 +-
 4 files changed, 729 insertions(+), 130 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/
[3] v3: https://lore.kernel.org/lkml/20260724215937.3368276-1-sumitg@nvidia.com/
[4] v4: https://lore.kernel.org/lkml/20260806200857.601152-1-sumitg@nvidia.com/
[5] v5: https://lore.kernel.org/lkml/20260916103820.1760297-1-sumitg@nvidia.com/
[6] v6: https://lore.kernel.org/lkml/20261020121846.691218-1-sumitg@nvidia.com/
[7] https://lore.kernel.org/lkml/1be30b2b-e1e5-41ed-a0dc-0dd5ad3c47cd@arm.com/
[8] https://lore.kernel.org/linux-pm/CAJZ5v0iXip_5Ywk3EkrGL_u2w_hOcGKA1XvrubLPb3diWHx5Lw@mail.gmail.com/

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2.34.1