linux-kernel - Re: [PATCH v1 5/6] clocksource/drivers/exynos

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Message-ID: <Z-wT3ciq7nL5wa1X@google.com>
Date: Tue, 1 Apr 2025 09:27:09 -0700
From: William McVicker <willmcvicker@...gle.com>
To: Krzysztof Kozlowski <krzk@...nel.org>
Cc: 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>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Saravana Kannan <saravanak@...gle.com>, kernel-team@...roid.com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-samsung-soc@...r.kernel.org, devicetree@...r.kernel.org,
	Donghoon Yu <hoony.yu@...sung.com>,
	Youngmin Nam <youngmin.nam@...sung.com>
Subject: Re: [PATCH v1 5/6] clocksource/drivers/exynos_mct: Add module support

On 04/01/2025, Krzysztof Kozlowski wrote:
> On 01/04/2025 01:00, 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.
> > 
> > Signed-off-by: Donghoon Yu <hoony.yu@...sung.com>
> > Signed-off-by: Youngmin Nam <youngmin.nam@...sung.com>
> > [Original commit from https://android.googlesource.com/kernel/gs/+/8a52a8288ec7d88ff78f0b37480dbb0e9c65bbfd]
> > Signed-off-by: Will McVicker <willmcvicker@...gle.com>
> > ---
> >  drivers/clocksource/Kconfig      |  3 +-
> >  drivers/clocksource/exynos_mct.c | 47 +++++++++++++++++++++++++++-----
> >  2 files changed, 42 insertions(+), 8 deletions(-)
> > 
> > diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
> > index 487c85259967..e5d9d8383607 100644
> > --- a/drivers/clocksource/Kconfig
> > +++ b/drivers/clocksource/Kconfig
> > @@ -443,7 +443,8 @@ config ATMEL_TCB_CLKSRC
> >  	  Support for Timer Counter Blocks on Atmel SoCs.
> >  
> >  config CLKSRC_EXYNOS_MCT
> > -	bool "Exynos multi core timer driver" if COMPILE_TEST
> > +	tristate "Exynos multi core timer driver"
> > +	default y if ARCH_EXYNOS
> >  	depends on ARM || ARM64
> >  	depends on ARCH_ARTPEC || ARCH_EXYNOS || COMPILE_TEST
> I am not sure if you actually tested it as module. On arm I cannot build
> it even:
> 
> ERROR: modpost: "register_current_timer_delay"
> [drivers/clocksource/exynos_mct.ko] undefined!
> ERROR: modpost: "sched_clock_register"
> [drivers/clocksource/exynos_mct.ko] undefined!

I tested with the gs101 ARM64 configuration. You're right it won't work with
ARM32. Thanks for catching this! Since ARM32 architectures don't have the
arch_timer, I'm not sure if we can actually support Exynos MCT as a module as
you wouldn't have any available clocksource during boot. I'll update the
Kconfig for v2 to handle this and make sure it works for ARM32. I'm guessing
it'll work with something like:

config CLKSRC_EXYNOS_MCT
	tristate "Exynos multi core timer driver" if ARM64


Regards,
Will

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