[Bug 218305] Ryzen 7 7840HS gets stuck at 544MHz frequency after resuming after unplugging the power cord during sleep

[bugzilla-daemon@kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=218305

--- Comment #153 from Artem S. Tashkinov (aros@gmx.com) ---
Mario, someone used Claude to dig into the issue and here's what it has to say:


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**Why it works on Windows:** AMD's Windows drivers explicitly re-initialize the
SMU CPPC handshake
in their resume path. The Linux `amd_pmc` and `amd-pstate` drivers do not.

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## How an upstream provider can fix this

### Kernel fix (correct layer — `amd-pstate` / `amd_pmc`)

`drivers/cpufreq/amd-pstate.c` — The driver needs a `.resume()` callback (or a
`syscore_ops.resume` hook) that re-writes the CPPC `desired_perf` register for
every online CPU.
In active mode this means re-issuing the CPPC performance request that was in
effect before
suspend, forcing the SMU to re-accept OS-side CPPC control.

`drivers/platform/x86/amd/pmc/pmc.c` — The `amd_pmc` driver orchestrates the
s2idle handshake.
On the exit path (`amd_pmc_resume_handler`) it could call a notifier that lets
`amd-pstate`
re-initialize CPPC, ensuring the SMU is back under kernel control before user
processes resume.

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Is this doable/plausible?

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