Booting v7.1-rc4 hangs on a single core CPU, bisected to ff1c0c5d07028

Booting v7.1-rc4 hangs on a single core CPU, bisected to ff1c0c5d07028

[Indrek Kruusa]

Hi,

booting Linux 7.1-rc4 on my Allwinner D1 (single core RISC-V) board
hangs during boot.
The last messages are MMC related, but further testing revealed that
the system hangs at  msleep()/usleep_range() calls.

I did an assisted bisect which points to this merge commit:
ff1c0c5d07028 Merge branch 'timers/urgent' into timers/core

I tried the suggested workaround "revert clockevents.c to the version
from 09c04714cb455" and it fixed the problem for me.

Can anyone with a single-core (RISC-V?) system confirm this? It seems
to be no issue on SMP.

Best regards,
Indrek

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[PATCH] clocksource/drivers/timer-sun4i: Advertise a real minimum delta

[Felix Yan]

sun4i_clkevt_next_event() compensates for the timer stop/start
synchronization delay by programming evt - TIMER_SYNC_TICKS into the
hardware interval register. The clockevent device currently advertises
TIMER_SYNC_TICKS as min_delta_ticks, so the clockevents core is allowed
to call set_next_event() with evt == TIMER_SYNC_TICKS.

That programs a zero-tick interval. With oneshot/highres/nohz timer
operation this can leave the next event stuck, which was observed as a
boot hang on Allwinner D1 after the clockevents core started reusing
forced minimum-delta events.

Advertise one extra tick instead, so the smallest event accepted by the
core still programs at least one hardware tick after the synchronization
compensation.

Fixes: 12e1480bcb49 ("clocksource: sun4i: Report the minimum tick that we can program")
Cc: stable@vger.kernel.org
Reported-by: Indrek Kruusa <indrek.kruusa@gmail.com>
Closes: https://lore.kernel.org/linux-riscv/CA+fTLhgLmTY+exGujKf8OYYQvcEW5X5NJ_5sLq2AYL6zER2c0A@mail.gmail.com/
Assisted-by: Codex:gpt-5.5
Signed-off-by: Felix Yan <felixonmars@archlinux.org>
---
 drivers/clocksource/timer-sun4i.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/clocksource/timer-sun4i.c b/drivers/clocksource/timer-sun4i.c
index 7bdcc60ad43c..c2d04ab7cf2d 100644
--- a/drivers/clocksource/timer-sun4i.c
+++ b/drivers/clocksource/timer-sun4i.c
@@ -208,7 +208,7 @@ static int __init sun4i_timer_init(struct device_node *node)
 	sun4i_timer_clear_interrupt(timer_of_base(&to));
 
 	clockevents_config_and_register(&to.clkevt, timer_of_rate(&to),
-					TIMER_SYNC_TICKS, 0xffffffff);
+					TIMER_SYNC_TICKS + 1, 0xffffffff);
 
 	/* Enable timer0 interrupt */
 	val = readl(timer_of_base(&to) + TIMER_IRQ_EN_REG);
-- 
2.54.0


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Re: [PATCH] clocksource/drivers/timer-sun4i: Advertise a real minimum delta

[Indrek Kruusa]

Hi Felix,

On Thu, 25 Jun 2026 06:04:34 +0800, Felix Yan wrote:
> sun4i_clkevt_next_event() compensates for the timer stop/start
> synchronization delay by programming evt - TIMER_SYNC_TICKS into the
> hardware interval register. The clockevent device currently advertises
> TIMER_SYNC_TICKS as min_delta_ticks, so the clockevents core is allowed
> to call set_next_event() with evt == TIMER_SYNC_TICKS.
>
> That programs a zero-tick interval. With oneshot/highres/nohz timer
> operation this can leave the next event stuck, which was observed as a
> boot hang on Allwinner D1 after the clockevents core started reusing
> forced minimum-delta events.
>
> Advertise one extra tick instead, so the smallest event accepted by the
> core still programs at least one hardware tick after the synchronization
> compensation.
>
> Fixes: 12e1480bcb49 ("clocksource: sun4i: Report the minimum tick that we can program")
> Cc: stable@vger.kernel.org
> Reported-by: Indrek Kruusa <indrek.kruusa@gmail.com>
> Closes: https://lore.kernel.org/linux-riscv/CA+fTLhgLmTY+exGujKf8OYYQvcEW5X5NJ_5sLq2AYL6zER2c0A@mail.gmail.com/
> Assisted-by: Codex:gpt-5.5
> Signed-off-by: Felix Yan <felixonmars@archlinux.org>
> ---
>  drivers/clocksource/timer-sun4i.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/clocksource/timer-sun4i.c b/drivers/clocksource/timer-sun4i.c
> index 7bdcc60ad43c..c2d04ab7cf2d 100644
> --- a/drivers/clocksource/timer-sun4i.c
> +++ b/drivers/clocksource/timer-sun4i.c
> @@ -208,7 +208,7 @@ static int __init sun4i_timer_init(struct device_node *node)
>  	sun4i_timer_clear_interrupt(timer_of_base(&to));
>  
>  	clockevents_config_and_register(&to.clkevt, timer_of_rate(&to),
> -					TIMER_SYNC_TICKS, 0xffffffff);
> +					TIMER_SYNC_TICKS + 1, 0xffffffff);
>  
>  	/* Enable timer0 interrupt */
>  	val = readl(timer_of_base(&to) + TIMER_IRQ_EN_REG);
> -- 
> 2.54.0

I can confirm that this patch makes my Allwinner D1 board boot
again with v7.1-rc1 and newer kernels.

Tested-by: Indrek Kruusa <indrek.kruusa@gmail.com>
Closes also: https://lore.kernel.org/regressions/20260531165138.2696250-1-indrek.kruusa@gmail.com/

Thank you,
Indrek

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Re: [PATCH] clocksource/drivers/timer-sun4i: Advertise a real minimum delta

[Jernej Škrabec]

Dne četrtek, 25. junij 2026 ob 00:04:34 Srednjeevropski poletni čas je Felix Yan napisal(a):
> sun4i_clkevt_next_event() compensates for the timer stop/start
> synchronization delay by programming evt - TIMER_SYNC_TICKS into the
> hardware interval register. The clockevent device currently advertises
> TIMER_SYNC_TICKS as min_delta_ticks, so the clockevents core is allowed
> to call set_next_event() with evt == TIMER_SYNC_TICKS.
> 
> That programs a zero-tick interval. With oneshot/highres/nohz timer
> operation this can leave the next event stuck, which was observed as a
> boot hang on Allwinner D1 after the clockevents core started reusing
> forced minimum-delta events.
> 
> Advertise one extra tick instead, so the smallest event accepted by the
> core still programs at least one hardware tick after the synchronization
> compensation.
> 
> Fixes: 12e1480bcb49 ("clocksource: sun4i: Report the minimum tick that we can program")
> Cc: stable@vger.kernel.org
> Reported-by: Indrek Kruusa <indrek.kruusa@gmail.com>
> Closes: https://lore.kernel.org/linux-riscv/CA+fTLhgLmTY+exGujKf8OYYQvcEW5X5NJ_5sLq2AYL6zER2c0A@mail.gmail.com/
> Assisted-by: Codex:gpt-5.5
> Signed-off-by: Felix Yan <felixonmars@archlinux.org>

Acked-by: Jernej Skrabec <jernej.skrabec@gmail.com>

Best regards,
Jernej



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