Re: [PATCH] clocksource/drivers/exynos_mct: only use IRQF_PERCPU flag on ARM64 SoCs

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

On 04.09.2025 17:32, Peter Griffin wrote:
> This patch addresses a regression reported in [1] whereby CPU hotplug now
> fails on little CPUs (for reasons that aren't fully understood) for Arm
> 32bit platforms such as Exynos 5422 used in OdroidXU3/XU4 boards.
>
> Note: This patch makes an assumption that the exynos_mct driver is only
> used on Arm 32/64 bit SoCs.
>
> Fixes: f3cec54ee3bf ("clocksource/drivers/exynos_mct: Set local timer interrupts as percpu")
> Reported-by: Marek Szyprowski <m.szyprowski@samsung.com>
> Closes: https://lore.kernel.org/lkml/8c861182-7e90-4bbf-ac04-173d59f5af69@samsung.com/
> Link: https://lore.kernel.org/lkml/8c861182-7e90-4bbf-ac04-173d59f5af69@samsung.com/ [1]
> Signed-off-by: Peter Griffin <peter.griffin@linaro.org>
> ---
> Hi Marek & Krzysztof,
>      
> Can you test this patch on your Exynos5422 based boards and see if it
> resolves the issue Marek reported of CPU hot plug failing on the little
> cores of Exynos 5422 based boards?
>
> Unfortunately I only have gs101 based Exynos hardware (which is Arm 64 bit
> SoC) to test on. I can confirm CPU hotplug is functional on the little
> cluster CPUs with IRQF_PERCPU flag on Pixel6/gs101 though.

This is a duplicate of 
https://lore.kernel.org/all/20250827102645.1964659-1-m.szyprowski@samsung.com/

and yes, it fixes the reported issue.

Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>

> Thanks,
>
> Peter
> ---
> ---
>   drivers/clocksource/exynos_mct.c | 13 +++++++++++--
>   1 file changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/clocksource/exynos_mct.c b/drivers/clocksource/exynos_mct.c
> index 62febeb4e1decec7f5db104db395884824563915..91d79b73a96a7e8a354d803c2b497bcde92af8d8 100644
> --- a/drivers/clocksource/exynos_mct.c
> +++ b/drivers/clocksource/exynos_mct.c
> @@ -532,6 +532,16 @@ static int __init exynos4_timer_resources(struct device_node *np)
>   	return 0;
>   }
>   
> +/*
> + * For reasons that aren't fully understood IRQF_PERCPU breaks CPU hotplug on
> + * little cores of ARM 32 bit SoCs like Exynos5422 used in OdroidXU3/4 boards.
> + */
> +#if defined(CONFIG_ARM64) || defined(CONFIG_COMPILE_TEST)
> +#define MCT_IRQ_FLAGS (IRQF_TIMER | IRQF_NOBALANCING | IRQF_PERCPU)
> +#elif defined(CONFIG_ARM)
> +#define MCT_IRQ_FLAGS (IRQF_TIMER | IRQF_NOBALANCING)
> +#endif
> +
>   /**
>    * exynos4_timer_interrupts - initialize MCT interrupts
>    * @np: device node for MCT
> @@ -602,8 +612,7 @@ static int __init exynos4_timer_interrupts(struct device_node *np,
>   			irq_set_status_flags(mct_irq, IRQ_NOAUTOEN);
>   			if (request_irq(mct_irq,
>   					exynos4_mct_tick_isr,
> -					IRQF_TIMER | IRQF_NOBALANCING |
> -					IRQF_PERCPU,
> +					MCT_IRQ_FLAGS,
>   					pcpu_mevt->name, pcpu_mevt)) {
>   				pr_err("exynos-mct: cannot register IRQ (cpu%d)\n",
>   									cpu);
>
> ---
> base-commit: 4ac65880ebca1b68495bd8704263b26c050ac010
> change-id: 20250904-exynos-mct-arm32-cpuhp-regression-14f321e4a591
>
> Best regards,

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