Re: [PATCH v5 6/7] clocksource/drivers/exynos_mct: Add module support

[William McVicker <willmcvicker@google.com>]

On 10/24/2025, Marek Szyprowski wrote:
> On 23.10.2025 22:52, Will McVicker wrote:
> > From: Donghoon Yu <hoony.yu@samsung.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@samsung.com>
> > Signed-off-by: Youngmin Nam <youngmin.nam@samsung.com>
> > Signed-off-by: Will McVicker <willmcvicker@google.com>
> > Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
> > [original commit from https://android.googlesource.com/kernel/gs/+/8a52a8288ec7d88ff78f0b37480dbb0e9c65bbfd]
> > Reviewed-by: Youngmin Nam <youngmin.nam@samsung.com> # AOSP -> Linux port
> > Tested-by: Youngmin Nam <youngmin.nam@samsung.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>