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[added,to,the,3.12,stable,tree] clocksource: vf_pit_timer: use complement for sched_clock reading

Message ID 1395827220-11701-8-git-send-email-jslaby@suse.cz (mailing list archive)
State New, archived
Headers show

Commit Message

Jiri Slaby March 26, 2014, 9:46 a.m. UTC 
From: Stefan Agner <stefan@agner.ch>

This patch has been added to the 3.12 stable tree. If you have any
objections, please let us know.
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Patch

===============

commit 224aa3ed45c8735ae02bb2ecca002409fa6aa772 upstream.

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 <stefan@agner.ch>
Acked-by: Shawn Guo <shawn.guo@linaro.org>
Cc: daniel.lezcano@linaro.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux@arm.linux.org.uk
Link: http://lkml.kernel.org/r/d25af915993aec1b486be653eb86f748ddef54fe.1394057313.git.stefan@agner.ch
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 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 587e0202a70b..e5590953630e 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 unsigned int 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)