linux-kernel - Re: [PATCH v2 6/7] clocksource/drivers/exynos

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Message-ID: <aCNctHq6K7uqFF05@mai.linaro.org>
Date: Tue, 13 May 2025 16:52:36 +0200
From: Daniel Lezcano <daniel.lezcano@...aro.org>
To: John Stultz <jstultz@...gle.com>
Cc: Will McVicker <willmcvicker@...gle.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>,
	Peter Griffin <peter.griffin@...aro.org>,
	André Draszik <andre.draszik@...aro.org>,
	Tudor Ambarus <tudor.ambarus@...aro.org>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Alim Akhtar <alim.akhtar@...sung.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Saravana Kannan <saravanak@...gle.com>,
	Krzysztof Kozlowski <krzk@...nel.org>,
	Donghoon Yu <hoony.yu@...sung.com>,
	Hosung Kim <hosung0.kim@...sung.com>, kernel-team@...roid.com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Youngmin Nam <youngmin.nam@...sung.com>,
	linux-samsung-soc@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH v2 6/7] clocksource/drivers/exynos_mct: Add module support

On Tue, Apr 15, 2025 at 05:48:41PM -0700, John Stultz wrote:
> On Tue, Apr 15, 2025 at 9:50 AM Daniel Lezcano
> <daniel.lezcano@...aro.org> wrote:
> > On Wed, Apr 02, 2025 at 04:33:57PM -0700, Will McVicker wrote:
> > > From: Donghoon Yu <hoony.yu@...sung.com>
> > >
> > > On Arm64 platforms the Exynos MCT driver can be built as a module. On
> > > boot (and even after boot) the arch_timer is used as the clocksource and
> > > tick timer. Once the MCT driver is loaded, it can be used as the wakeup
> > > source for the arch_timer.
> >
> > From a previous thread where there is no answer:
> >
> > https://lore.kernel.org/all/c1e8abec-680c-451d-b5df-f687291aa413@linaro.org/
> >
> > I don't feel comfortable with changing the clocksource / clockevent drivers to
> > a module for the reasons explained in the aforementionned thread.
> 
> I wasn't CC'ed on that, but to address a few of your points:
> 
> > I have some concerns about this kind of changes:
> >
> >   * the core code may not be prepared for that, so loading / unloading
> > the modules with active timers may result into some issues
> 
> That's a fair concern, but permanent modules (which are loaded but not
> unloaded) shouldn't suffer this issue. I recognize having modules be
> fully unloadable is generally cleaner and preferred, but I also see
> the benefit of allowing permanent modules to be one-way loaded so a
> generic/distro kernel shared between lots of different platforms
> doesn't need to be bloated with drivers that aren't used everywhere.
> Obviously any single driver doesn't make a huge difference, but all
> the small drivers together does add up.

Perhaps using module_platform_driver_probe() should do the trick with
some scripts updated for my git hooks to check
module_platform_driver() is not used.

[ ... ]

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