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@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/

-- 
2.34.1

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@amd.com>

-- 
Thanks and Regards,
Prateek

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@amd.com>
> 
> --
> 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