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

[Sumit Gupta]

On 17/09/26 00:34, K Prateek Nayak wrote:
> External email: Use caution opening links or attachments
>
>
> Hello Sumit,
>
> On 9/16/2026 4:08 PM, Sumit Gupta 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(-)
>
> I was able to hack the Kconfig to build cppc_cpufreq.c for x86 too
> and test this out on a Zen3 machine that uses shared memory based
> CPPC control.
>
> FWIW, I could verify that "auto_select" and
> "energy_performance_preference_val" persists correctly across an
> offline-online cycle on my system so feel free to include:
>
> Tested-by: K Prateek Nayak <kprateek.nayak@xxxxxxx>
>
> --
> Thanks and Regards,
> Prateek

Hi Prateek,

Thanks for testing on x86.
I will add your Tested-by to the series, and Reviewed-by to patch 2.

Thanks,
Sumit