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From: (Stefan Agner)
Subject: [PATCH] clocksource: vf_pit_timer: use complement for sched_clock reading
Date: Wed,  5 Mar 2014 23:11:08 +0100
Message-ID: <> (raw)

Vybrids PIT register is monitonic decreasing. However, sched_clock
reading needs to be monitonic increasing. Use bitwise not to get
the complement of the clock register. This fixes the clock going
backward. Also, the clock now starts at 0 since we load the
register with the maximum value at start.

Signed-off-by: Stefan Agner <>
 drivers/clocksource/vf_pit_timer.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/clocksource/vf_pit_timer.c b/drivers/clocksource/vf_pit_timer.c
index 02821b0..a918bc4 100644
--- a/drivers/clocksource/vf_pit_timer.c
+++ b/drivers/clocksource/vf_pit_timer.c
@@ -54,7 +54,7 @@ static inline void pit_irq_acknowledge(void)
 static u64 pit_read_sched_clock(void)
-	return __raw_readl(clksrc_base + PITCVAL);
+	return ~__raw_readl(clksrc_base + PITCVAL);
 static int __init pit_clocksource_init(unsigned long rate)

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Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-03-05 22:11 Stefan Agner [this message]
2014-03-06  1:45 ` Shawn Guo
2014-03-06  3:18   ` Jingchang Lu

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