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Message-ID: <aPuhDFKINM9iXOKb@google.com>
Date: Fri, 24 Oct 2025 15:53:48 +0000
From: William McVicker <willmcvicker@...gle.com>
To: Marek Szyprowski <m.szyprowski@...sung.com>
Cc: Russell King <linux@...linux.org.uk>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>,
Daniel Lezcano <daniel.lezcano@...aro.org>,
Thomas Gleixner <tglx@...utronix.de>,
Krzysztof Kozlowski <krzk@...nel.org>,
Alim Akhtar <alim.akhtar@...sung.com>,
Ingo Molnar <mingo@...nel.org>,
Peter Griffin <peter.griffin@...aro.org>,
Youngmin Nam <youngmin.nam@...sung.com>,
Donghoon Yu <hoony.yu@...sung.com>, Rob Herring <robh@...nel.org>,
Saravana Kannan <saravanak@...gle.com>,
John Stultz <jstultz@...gle.com>,
Tudor Ambarus <tudor.ambarus@...aro.org>,
André Draszik <andre.draszik@...aro.org>,
Conor Dooley <conor+dt@...nel.org>,
linux-samsung-soc@...r.kernel.org, kernel-team@...roid.com,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 6/7] clocksource/drivers/exynos_mct: Add module support
On 10/24/2025, Marek Szyprowski wrote:
> On 23.10.2025 22:52, 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>
> > Signed-off-by: Will McVicker <willmcvicker@...gle.com>
> > Signed-off-by: Daniel Lezcano <daniel.lezcano@...aro.org>
> > [original commit from https://android.googlesource.com/kernel/gs/+/8a52a8288ec7d88ff78f0b37480dbb0e9c65bbfd]
> > Reviewed-by: Youngmin Nam <youngmin.nam@...sung.com> # AOSP -> Linux port
> > Tested-by: Youngmin Nam <youngmin.nam@...sung.com> # AOSP -> Linux port
> > ---
> > drivers/clocksource/Kconfig | 3 +-
> > drivers/clocksource/exynos_mct.c | 56 +++++++++++++++++++++++++++-----
> > 2 files changed, 49 insertions(+), 10 deletions(-)
> >
> > diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
> > index ffcd23668763..9450cfaf982f 100644
> > --- a/drivers/clocksource/Kconfig
> > +++ b/drivers/clocksource/Kconfig
> > @@ -451,7 +451,8 @@ 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" if ARM64
> > + default y if ARCH_EXYNOS || COMPILE_TEST
> > depends on ARM || ARM64
> > depends on ARCH_ARTPEC || ARCH_EXYNOS || COMPILE_TEST
> > help
> > diff --git a/drivers/clocksource/exynos_mct.c b/drivers/clocksource/exynos_mct.c
> > index fece6bbc190e..a87caf3928ef 100644
> > --- a/drivers/clocksource/exynos_mct.c
> > +++ b/drivers/clocksource/exynos_mct.c
> > @@ -15,9 +15,11 @@
> > #include <linux/cpu.h>
> > #include <linux/delay.h>
> > #include <linux/percpu.h>
> > +#include <linux/module.h>
> > #include <linux/of.h>
> > #include <linux/of_irq.h>
> > #include <linux/of_address.h>
> > +#include <linux/platform_device.h>
> > #include <linux/clocksource.h>
> > #include <linux/sched_clock.h>
> >
> > @@ -217,6 +219,7 @@ static struct clocksource mct_frc = {
> > .mask = CLOCKSOURCE_MASK(32),
> > .flags = CLOCK_SOURCE_IS_CONTINUOUS,
> > .resume = exynos4_frc_resume,
> > + .owner = THIS_MODULE,
> > };
> >
> > /*
> > @@ -241,7 +244,7 @@ static cycles_t exynos4_read_current_timer(void)
> > }
> > #endif
> >
> > -static int __init exynos4_clocksource_init(bool frc_shared)
> > +static int exynos4_clocksource_init(bool frc_shared)
> > {
> > /*
> > * When the frc is shared, the main processor should have already
> > @@ -336,6 +339,7 @@ static struct clock_event_device mct_comp_device = {
> > .set_state_oneshot = mct_set_state_shutdown,
> > .set_state_oneshot_stopped = mct_set_state_shutdown,
> > .tick_resume = mct_set_state_shutdown,
> > + .owner = THIS_MODULE,
> > };
> >
> > static irqreturn_t exynos4_mct_comp_isr(int irq, void *dev_id)
> > @@ -476,6 +480,7 @@ static int exynos4_mct_starting_cpu(unsigned int cpu)
> > evt->features = CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT |
> > CLOCK_EVT_FEAT_PERCPU;
> > evt->rating = MCT_CLKEVENTS_RATING;
> > + evt->owner = THIS_MODULE;
> >
> > exynos4_mct_write(TICK_BASE_CNT, mevt->base + MCT_L_TCNTB_OFFSET);
> >
> > @@ -511,7 +516,7 @@ static int exynos4_mct_dying_cpu(unsigned int cpu)
> > return 0;
> > }
> >
> > -static int __init exynos4_timer_resources(struct device_node *np)
> > +static int exynos4_timer_resources(struct device_node *np)
> > {
> > struct clk *mct_clk, *tick_clk;
> >
> > @@ -539,7 +544,7 @@ static int __init exynos4_timer_resources(struct device_node *np)
> > * @local_idx: array mapping CPU numbers to local timer indices
> > * @nr_local: size of @local_idx array
> > */
> > -static int __init exynos4_timer_interrupts(struct device_node *np,
> > +static int exynos4_timer_interrupts(struct device_node *np,
> > unsigned int int_type,
> > const u32 *local_idx,
> > size_t nr_local)
> > @@ -653,7 +658,7 @@ static int __init exynos4_timer_interrupts(struct device_node *np,
> > return err;
> > }
> >
> > -static int __init mct_init_dt(struct device_node *np, unsigned int int_type)
> > +static int mct_init_dt(struct device_node *np, unsigned int int_type)
> > {
> > bool frc_shared = of_property_read_bool(np, "samsung,frc-shared");
> > u32 local_idx[MCT_NR_LOCAL] = {0};
> > @@ -701,15 +706,48 @@ static int __init mct_init_dt(struct device_node *np, unsigned int int_type)
> > return exynos4_clockevent_init();
> > }
> >
> > -
> > -static int __init mct_init_spi(struct device_node *np)
> > +static int mct_init_spi(struct device_node *np)
> > {
> > return mct_init_dt(np, MCT_INT_SPI);
> > }
> >
> > -static int __init mct_init_ppi(struct device_node *np)
> > +static int mct_init_ppi(struct device_node *np)
> > {
> > return mct_init_dt(np, MCT_INT_PPI);
> > }
> > -TIMER_OF_DECLARE(exynos4210, "samsung,exynos4210-mct", mct_init_spi);
> > -TIMER_OF_DECLARE(exynos4412, "samsung,exynos4412-mct", mct_init_ppi);
> > +
> > +static int exynos4_mct_probe(struct platform_device *pdev)
> > +{
> > + struct device *dev = &pdev->dev;
> > + int (*mct_init)(struct device_node *np);
> > +
> > + mct_init = of_device_get_match_data(dev);
> > + if (!mct_init)
> > + return -EINVAL;
> > +
> > + return mct_init(dev->of_node);
> > +}
> > +
> > +static const struct of_device_id exynos4_mct_match_table[] = {
> > + { .compatible = "samsung,exynos4210-mct", .data = &mct_init_spi, },
> > + { .compatible = "samsung,exynos4412-mct", .data = &mct_init_ppi, },
> > + {}
> > +};
> > +MODULE_DEVICE_TABLE(of, exynos4_mct_match_table);
> > +
> > +static struct platform_driver exynos4_mct_driver = {
> > + .probe = exynos4_mct_probe,
> > + .driver = {
> > + .name = "exynos-mct",
> > + .of_match_table = exynos4_mct_match_table,
> > + },
> > +};
> > +
> > +static __init int exynos_mct_init(void)
> > +{
> > + return platform_driver_register(&exynos4_mct_driver);
> > +}
> > +module_init(exynos_mct_init);
> > +
> > +MODULE_DESCRIPTION("Exynos Multi Core Timer Driver");
> > +MODULE_LICENSE("GPL");
>
> Sorry, but this still won't work on legacy ARM 32bit systems with MCT as
> the only clocksource, which needs a driver available very early (that's
> why it used TIMER_OF_DECLAREmacro). You need to make it conditional
> under CONFIG_ARM:
Can we rely on the bootloader to setup the MCT timer and then hand-off at boot
once the driver is initialized?
Daniel was working on a solution to transparently handle calling
TIMER_OF_DECLARE() when a timer driver can be configured as both a module or
built-in here:
https://lore.kernel.org/all/20250625085715.889837-1-daniel.lezcano@linaro.org/
Daniel, do you have plans to finish that? In the meantime, can we go with the
`#if CONFIG_ARM` solution?
Thanks,
Will
<snip>
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