[PATCH] clocksource/drivers/timer-mediatek: Enable the GPT irq before registering

[Chen-Yu Tsai]

On Wed, Nov 4, 2026 at 8:18 AM Ryan Brue <ryanbrue.dev at gmail.com> wrote:
>
> Since the driver probes as a platform device, the GPT clock event is
> registered late in boot, when PSCI CPU idle may already have put CPUs
> into a state that stops their local timer. Those CPUs wait in the
> oneshot broadcast mask on the hrtimer broadcast, and
> tick_install_broadcast_device() arms the new broadcast device to expire
> at once so that it wakes them.
>
> mtk_gpt_init() sets the timer's bit in GPT_IRQ_EN only after
> clockevents_config_and_register(). The forced event fires while the bit
> is clear, nothing is latched in the status register, and the waiting
> CPUs are never woken. On an MT8173 tablet with the CPU_SLEEP_0 idle
> state in use, this hung the boot in 20 of 40 boots, and in none of 16
> with this change.
>
> Enable the interrupt before registering the clock event. The IRQ line
> stays disabled until enable_irq(), so the handler still can't run before
> the clock event is set up.
>
> Fixes: 7a097aba7255 ("clocksource/drivers/timer-mediatek: Convert to OF probing")
> Signed-off-by: Ryan Brue <ryanbrue.dev at gmail.com>

This seems to have fixed the cpuidle related stalls I was seeing. I
didn't do that many rounds of boot tests though.

Tested-by: Chen-Yu Tsai <wenst at chromium.org> # on Hana (Telesu)
Reviewed-by: Chen-Yu Tsai <wenst at chromium.org>

I do think we should expedite this into the kernel, as a 50% chance
of stalling is not great. It was even higher for me and somehow I
had to do a hard power cycle by rebooting the EC to get it unstuck.

> ---
> Since v7.4-rc1 the MediaTek timer probes as a platform device, and on
> MT8173 with PSCI CPU idle the boot then hangs about half the time: the
> broadcast device is armed at once to wake CPUs that are already idle,
> and that event is lost because the GPT's interrupt is enabled only after
> registration. Traced on the board with prints in
> tick_install_broadcast_device() and mtk_gpt_init().
> ---
>  drivers/clocksource/timer-mediatek.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/clocksource/timer-mediatek.c b/drivers/clocksource/timer-mediatek.c
> index 842d6ee4259e..1b2cbcc2795a 100644
> --- a/drivers/clocksource/timer-mediatek.c
> +++ b/drivers/clocksource/timer-mediatek.c
> @@ -339,10 +339,10 @@ static int mtk_gpt_init(struct platform_device *pdev)
>
>         /* Configure clock event */
>         mtk_gpt_setup(&to, TIMER_CLK_EVT, GPT_CTRL_OP_REPEAT);
> +       mtk_gpt_enable_irq(&to, TIMER_CLK_EVT);
>         clockevents_config_and_register(&to.clkevt, timer_of_rate(&to),
>                                         TIMER_SYNC_TICKS, 0xffffffff);
>
> -       mtk_gpt_enable_irq(&to, TIMER_CLK_EVT);
>         enable_irq(timer_of_irq(&to));
>
>         return 0;
>
> ---
> base-commit: 6628e7d4c6b25c8d18f1345e3a20d21829aae7e4
> change-id: 20261103-timer-mediatek-gpt-irq-order-a878ed869f84
>
> Best regards,
> --
> Ryan Brue <ryanbrue.dev at gmail.com>
>
>