linux-kernel - [PATCH] PM: fix calculation mistake in roll-over cases

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Message-Id: <1319538052-2480-1-git-send-email-vbyravarasu@nvidia.com>
Date:	Tue, 25 Oct 2011 15:50:52 +0530
From:	vbyravarasu@...dia.com
To:	pavel@....cz, rjw@...k.pl, len.brown@...el.com, gregkh@...e.de
Cc:	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
	vbyravarasu@...dia.com
Subject: [PATCH] PM: fix calculation mistake in roll-over cases

From: venu byravarasu <vbyravarasu@...dia.com>

In case of jiffies roll over, delta is made zero.
Hence fixing it, after taking roll over into consideration.

Signed-off-by: venu byravarasu <vbyravarasu@...dia.com>
---
When jiffies roll over, calculation of time spent in the
current state (stored in variable 'delta') is incorrect.
Hence fixing it, after taking roll over into consideration.

 drivers/base/power/runtime.c |    7 ++++---
 1 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/base/power/runtime.c b/drivers/base/power/runtime.c
index 1079e03..bd93fb0 100644
--- a/drivers/base/power/runtime.c
+++ b/drivers/base/power/runtime.c
@@ -30,12 +30,13 @@ static int rpm_suspend(struct device *dev, int rpmflags);
 void update_pm_runtime_accounting(struct device *dev)
 {
 	unsigned long now = jiffies;
-	int delta;
+	unsigned long delta;
+	unsigned long max_num = ~0;
 
 	delta = now - dev->power.accounting_timestamp;
 
-	if (delta < 0)
-		delta = 0;
+	if (now < dev->power.accounting_timestamp)
+		delta = max_num - dev->power.accounting_timestamp + now;
 
 	dev->power.accounting_timestamp = now;
 
-- 
1.7.1.1

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