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

On Wed, Aug 26, 2026 at 11:07 AM Christian Loehle
<[email protected]> wrote:
>
> 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())

I agree.

Besides, as I said elsewhere, I want this series to go in before any
other pending changes related to CPPC:

https://lore.kernel.org/linux-acpi/[email protected]/

and I really would like to get some tags on it before it goes in.  It
clearly is not ready for 7.3, but it may be applicable early for 7.4
if people care to respond to it.

Thanks!