linux-kernel - [PATCH 62/69] clocksource/drivers/pistachio: Fix wrong calculated clocksource read value

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Message-Id: <1450448302-27429-62-git-send-email-daniel.lezcano@linaro.org>
Date:	Fri, 18 Dec 2015 15:18:15 +0100
From:	Daniel Lezcano <daniel.lezcano@...aro.org>
To:	tglx@...utronix.de
Cc:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	mingo@...nel.org, Jisheng Zhang <jszhang@...vell.com>
Subject: [PATCH 62/69] clocksource/drivers/pistachio: Fix wrong calculated clocksource read value

From: Jisheng Zhang <jszhang@...vell.com>

Let's assume the counter value is 0xf0000000, the pistachio clocksource
read cycles function should return ~0x0fffffff but actually it returns
0xffffffff0fffffff.

That occurs because:

	~(cycle_t)value is different from (cycle_t)~value.

unsigned long val = ~(unsigned long)0xf0000000;
40049a:       48 b8 ff ff ff 0f ff    movabs $0xffffffff0fffffff,%rax

unsigned long val = (unsigned long)~0xf0000000;
40049a:       48 c7 45 f8 ff ff ff    movq   $0xfffffff,-0x8(%rbp)

We fix this issue by calculating bitwise-not counter, then cast to
cycle_t.

Signed-off-by: Jisheng Zhang <jszhang@...vell.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@...aro.org>
---
 drivers/clocksource/time-pistachio.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/clocksource/time-pistachio.c b/drivers/clocksource/time-pistachio.c
index bba6799..3269d9e 100644
--- a/drivers/clocksource/time-pistachio.c
+++ b/drivers/clocksource/time-pistachio.c
@@ -84,7 +84,7 @@ pistachio_clocksource_read_cycles(struct clocksource *cs)
 	counter = gpt_readl(pcs->base, TIMER_CURRENT_VALUE, 0);
 	raw_spin_unlock_irqrestore(&pcs->lock, flags);
 
-	return ~(cycle_t)counter;
+	return (cycle_t)~counter;
 }
 
 static u64 notrace pistachio_read_sched_clock(void)
-- 
1.9.1

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