Re: [PATCH v5 0/4] cpufreq: CPPC: Preserve OSPM-set registers across hotplug and unload

[Rafael J. Wysocki (Intel)]

On Wed, Sep 16, 2026 at 12:39 PM Sumit Gupta <sumitg@xxxxxxxxxx> wrote:
>
> 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).
>
> 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 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 at init(), restores it from offline(), and reapplies
>    the OSPM-set value from online().
>  - Patch 4: extends the same save/restore to system suspend/resume.
>
> v4[4] -> v5:
>  - Patch 1:
>    - offline() stops the frequency invariance updates and online()
>      restarts them, replacing the resync that raced with tick. (Sashiko)
>    - reorder the functions to match cppc_cpufreq_driver. (Jie Zhan)
>  - Patch 3:
>    - reapply the OSPM-set registers even when the performance control
>      write fails. (Sashiko)
>  - Patch 4:
>    - suspend() stops the frequency invariance updates too, completing the
>      patch 1 change for a policy whose CPUs stay online.
>
> 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 | 378 ++++++++++++++++++++++++++++++++-
>  include/acpi/cppc_acpi.h       |   8 +-
>  4 files changed, 381 insertions(+), 27 deletions(-)
>
> [1] v1: https://lore.kernel.org/lkml/20260623095403.3407436-1-sumitg@xxxxxxxxxx/
> [2] v2: https://lore.kernel.org/lkml/20260716153820.2007095-1-sumitg@xxxxxxxxxx/
> [3] v3: https://lore.kernel.org/lkml/20260724215937.3368276-1-sumitg@xxxxxxxxxx/
> [4] v4: https://lore.kernel.org/lkml/20260806200857.601152-1-sumitg@xxxxxxxxxx/
>
> --

Dear CPPC cpufreq driver reviewers, I need your input on this series.

It is not going to be applied without any input from anyone.

Thanks!