Re: [PATCH v4 0/4] cpufreq: CPPC: Preserve OSPM-set registers across hotplug and unload

[Sumit Gupta <sumitg@nvidia.com>]

On 07/08/26 01:38, 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.

Gentle reminder.
Could this be considered for queuing if nothing further needs addressing.

Thanks,
Sumit


> v3[3] -> v4:
>   - Patch 1:
>     - offline() parks the perf request at lowest_perf, as exit() did.
>     - online() resyncs the frequency invariance counters.
>     - raise MAX before the perf restore when the saved MIN is above it.
>   - Patch 3:
>     - write auto_sel first when enabling it and last when disabling it.
>     - replace the four save/restore helpers into save_regs() and
>       apply_saved_regs(), each taking the firmware or requested type.
>     - keep the per-policy saved values in one struct, and name each
>       register for the pr_debug diagnostics.
>   - Patch 4:
>     - suspend() also restores the firmware values and flags it, so
>       offline() skips them and resume() only handles still-online policies.
>
> 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 | 369 ++++++++++++++++++++++++++++++++-
>   include/acpi/cppc_acpi.h       |   8 +-
>   4 files changed, 376 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/
> [3] v3: https://lore.kernel.org/lkml/20260724215937.3368276-1-sumitg@nvidia.com/
>