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

[tip-bot2 for Felix Yan]

The following commit has been merged into the timers/clocksource branch of tip:

Commit-ID:     d21808328225ab8cee46885bf9a0dffcefbe630e
Gitweb:        https://git.kernel.org/tip/d21808328225ab8cee46885bf9a0dffcefbe630e
Author:        Felix Yan <felixonmars@xxxxxxxxxxxxx>
AuthorDate:    Thu, 25 Jun 2026 06:04:34 +08:00
Committer:     Daniel Lezcano <daniel.lezcano@xxxxxxxxxx>
CommitterDate: Thu, 13 Aug 2026 18:13:01 +02:00

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

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")
Reported-by: Indrek Kruusa <indrek.kruusa@xxxxxxxxx>
Closes: https://lore.kernel.org/linux-riscv/CA+fTLhgLmTY+exGujKf8OYYQvcEW5X5NJ_5sLq2AYL6zER2c0A@xxxxxxxxxxxxxx/
Assisted-by: Codex:gpt-5.5
Signed-off-by: Felix Yan <felixonmars@xxxxxxxxxxxxx>
Signed-off-by: Daniel Lezcano <daniel.lezcano@xxxxxxxxxx>
Tested-by: Indrek Kruusa <indrek.kruusa@xxxxxxxxx>
Acked-by: Jernej Skrabec <jernej.skrabec@xxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Link: https://lore.kernel.org/linux-riscv/CA+fTLhgLmTY+exGujKf8OYYQvcEW5X5NJ_5sLq2AYL6zER2c0A@xxxxxxxxxxxxxx/
Link: https://patch.msgid.link/20260624220434.4183732-1-felixonmars@xxxxxxxxxxxxx
---
 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 7bdcc60..c2d04ab 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);