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

[Christian Loehle]

On 8/25/26 22:20, Sumit Gupta wrote:
> 
> 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.

FWIW both sashiko findings look legit to me, the feedback counters one I
wouldn't consider that drastic, given that these counters are expected to
have 'fuzzy' readings anyhow, the second one is worse (losing sysfs settings
on cpu_online())