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

[Marek Szyprowski <m.szyprowski@samsung.com>]

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:

#ifdef CONFIG_ARM

TIMER_OF_DECLARE(exynos4210, "samsung,exynos4210-mct", mct_init_spi);
TIMER_OF_DECLARE(exynos4412, "samsung,exynos4412-mct", mct_init_ppi);

#else

... (module-based intialization).

#endif

The latter case might skip the legacy exynos4412-style case, as all MCT 
variants used on ARM 64bit systems are exynos4210 compatible.

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland