linux-kernel - Re: [PATCH v3 2/3] firmware: add exynos ACPM protocol driver

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Message-ID: <CADrjBPo_YmTuuW9c3LtWzMp7Sf4365e2bxuuYBUiFPPc42d1dA@mail.gmail.com>
Date: Wed, 11 Dec 2024 12:13:39 +0000
From: Peter Griffin <peter.griffin@...aro.org>
To: Daniel Lezcano <daniel.lezcano@...aro.org>
Cc: Krzysztof Kozlowski <krzk@...nel.org>, Tudor Ambarus <tudor.ambarus@...aro.org>, robh@...nel.org, 
	krzk+dt@...nel.org, conor+dt@...nel.org, alim.akhtar@...sung.com, 
	linux-kernel@...r.kernel.org, linux-samsung-soc@...r.kernel.org, 
	devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	andre.draszik@...aro.org, kernel-team@...roid.com, willmcvicker@...gle.com, 
	javierm@...hat.com, tzimmermann@...e.de, vincent.guittot@...aro.org, 
	ulf.hansson@...aro.org, arnd@...db.de
Subject: Re: [PATCH v3 2/3] firmware: add exynos ACPM protocol driver

Hi Daniel,

Thanks for your review feedback.

On Fri, 6 Dec 2024 at 19:50, Daniel Lezcano <daniel.lezcano@...aro.org> wrote:
>
> On 12/6/24 14:28, Krzysztof Kozlowski wrote:
> > On Fri, Dec 06, 2024 at 12:39:56AM +0100, Daniel Lezcano wrote:
> >>> +# SPDX-License-Identifier: GPL-2.0-only
> >>> +
> >>> +config EXYNOS_ACPM_PROTOCOL
> >>> +   tristate "Exynos Alive Clock and Power Manager (ACPM) Message Protocol"
> >>
> >> Given the importance of this driver where a lot of PM services rely on, does
> >> it really make sense to allow it as a module ?

Yes, we want the option to build it as a module so we can use the
upstreamed driver with Generic Kernel Image (GKI) [1].

> >>
> >> Some PM services may be needed very early in the boot process
> >>
> >
> > If it works as module e.g. on Android, it is beneficial. I think the
> > platform was booting fine without it, at least to some shell, so I can
> > imagine this can be loaded a bit later.
>
> Usually the firmware sets the frequency to the maximum in order to boot
> the kernel as fast as possible. That may lead to thermal issues at boot
> time where the thermal framework won't be able to kick in as some
> components will depends on ACPM while the system stays at its highest
> performance state.

That isn't an issue here as the Pixel 6 bootloader leaves CPUs at mid
point frequencies during boot. I would actually expect most modern
phone bootloaders (since the launch of GKI at least) to do something
similar as it is a requirement for Generic Kernel Image (GKI) [1] that
all the SoC drivers are built as modules.

[1] https://source.android.com/docs/core/architecture/kernel/generic-kernel-image

Thanks,

Peter