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@xxxxxxxxxxx>
> Closes: https://lore.kernel.org/lkml/8c861182-7e90-4bbf-ac04-173d59f5af69@xxxxxxxxxxx/
> Link: https://lore.kernel.org/lkml/8c861182-7e90-4bbf-ac04-173d59f5af69@xxxxxxxxxxx/ [1]
> Signed-off-by: Peter Griffin <peter.griffin@xxxxxxxxxx>
> ---
> 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@xxxxxxxxxxx/
and yes, it fixes the reported issue.
Tested-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
> 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
