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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <aCUkN301jWUkXJ3_@google.com>
Date: Wed, 14 May 2025 16:16:07 -0700
From: William McVicker <willmcvicker@...gle.com>
To: Daniel Lezcano <daniel.lezcano@...aro.org>
Cc: John Stultz <jstultz@...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 05/13/2025, Daniel Lezcano wrote:
> 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.

Using `module_platform_driver_probe()` won't work as that still defines
a `module_exit()` hook. If you want to automatically handle this in code, then
the best approach is to follow what Saravana did in [1] for irqchip drivers.
Basically by using `builtin_platform_driver(drv_name##_driver)`, you will only
define the `module_init()` hook when the driver is compiled as a module which
ensures you always get a permanent module.

[1] https://lore.kernel.org/linux-arm-kernel/20200718000637.3632841-1-saravanak@google.com/

Regards,
Will

[...]