linux-kernel - Re: [PATCH v6] soc: samsung: exynos-pmu: Enable CPU Idle for gs101

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Message-ID: <CADrjBPrRbSYXVg5KyNB8Z9qLkZ2sGzEUcP+nf2UP2rVm2T7bSQ@mail.gmail.com>
Date: Fri, 11 Jul 2025 16:49:39 +0100
From: Peter Griffin <peter.griffin@...aro.org>
To: Sudeep Holla <sudeep.holla@....com>
Cc: André Draszik <andre.draszik@...aro.org>, 
	Tudor Ambarus <tudor.ambarus@...aro.org>, Alim Akhtar <alim.akhtar@...sung.com>, 
	Krzysztof Kozlowski <krzk@...nel.org>, William Mcvicker <willmcvicker@...gle.com>, 
	Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>, linux-arm-kernel@...ts.infradead.org, 
	linux-samsung-soc@...r.kernel.org, linux-kernel@...r.kernel.org, 
	kernel-team@...roid.com
Subject: Re: [PATCH v6] soc: samsung: exynos-pmu: Enable CPU Idle for gs101

Hi Sudeep,

On Fri, 11 Jul 2025 at 15:56, Sudeep Holla <sudeep.holla@....com> wrote:
>
> On Fri, Jul 11, 2025 at 03:53:17PM +0100, Sudeep Holla wrote:
> > On Fri, Jul 11, 2025 at 02:50:26PM +0100, Peter Griffin wrote:
> > > Register cpu pm notifiers for gs101 which call the
> > > gs101_cpu_pmu_online/offline callbacks which in turn program the ACPM
> > > C2 hint. This hint is required to actually enter the C2 idle state in
> > > addition to the PSCI calls due to limitations in the firmare.
> > >
> > > A couple of corner cases are handled, namely when the system is rebooting
> > > or suspending we ignore the request. Additionally the request is ignored if
> > > the CPU is in CPU hot plug. Some common code is refactored so that it can
> > > be called from both the CPU hot plug callbacks and CPU PM notifier taking
> > > into account that CPU PM notifiers are called with IRQs disabled whereas
> > > CPU hotplug callbacks are not.
> > >
> > > Additionally due to CPU PM notifiers using raw_spinlock the locking is
> > > updated to use raw_spinlock variants, this includes updating the pmu_regs
> > > regmap to use .use_raw_spinlock = true and additionally creating and
> > > registering a custom  pmu-intr-gen regmap instead of using the regmap
> > > provided by syscon.
> > >
> > > Note: this patch has a runtime dependency on adding 'local-timer-stop' dt
> > > property to the CPU nodes. This informs the time framework to switch to a
> > > broadcast timer as the local timer will be shutdown. Without that DT
> > > property specified the system hangs in early boot with this patch applied.
> > >
> > > Signed-off-by: Peter Griffin <peter.griffin@...aro.org>
> > > ---
> > > Hi folks,
> > >
> > > This patch adds support for CPU Idle on gs101. In particular it achieves
> > > this by registerring a cpu pm notifier and programming a ACPM hint. This is
> > > required in addition to the PSCI calls to enter the c2 idle state due to
> > > limitations in the el3mon/ACPM firmware.
> > >
> >
> > I would rather keep the above note as part of the commit message or the
> > code comment as this will get lost when the patch is applied which is not
> > something we want. I clearly want to loudly shout or shame the broken
> > firmware for not getting this right.
> >
>
> I did see the comment but still thought it is worth adding the note in the
> commit log too. Sorry for referring code comment above which is wrong as it
> is already taken care.

I mentioned it in the commit log, a comment in the code and also the
cover letter so I think we should be all good? In the commit log it is
part of the first paragraph.

Thanks,

Peter