linux-kernel - [PATCH] timers: fix offset calculation when the expires align with LVL

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Date:   Fri, 27 Jul 2018 13:33:30 +0800
From:   Xu YiPing <xuyiping@...ilicon.com>
To:     <xuyiping@...ilicon.com>, <tglx@...utronix.de>,
        <john.stultz@...aro.org>, <sboyd@...nel.org>
CC:     <linux-kernel@...r.kernel.org>
Subject: [PATCH] timers: fix offset calculation when the expires align with LVL_GRAN

when the expires of timer is align with LVL_GRAN(n), it will be trigged
in 'expires + LVL_GRAN(n)'.

Some drivers like power runtime use the timer to start a power down
of device, it could saves power if the timer is triggerd in time,
especially when LEVEL=0 with low expires.

Signed-off-by: Xu YiPing <xuyiping@...ilicon.com>
---
 kernel/time/timer.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index cc2d23e..76655e2 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -487,7 +487,8 @@ static inline void timer_set_idx(struct timer_list *timer, unsigned int idx)
  */
 static inline unsigned calc_index(unsigned expires, unsigned lvl)
 {
-	expires = (expires + LVL_GRAN(lvl)) >> LVL_SHIFT(lvl);
+	expires = (expires + LVL_GRAN(lvl) - 1) >> LVL_SHIFT(lvl);
+
 	return LVL_OFFS(lvl) + (expires & LVL_MASK);
 }
 
-- 
2.7.4