[PATCH v3 2/3] devfreq: add clearing transitions stats

[Kamil Konieczny <k.konieczny@samsung.com>]

Add clearing transition table and time in states devfreq statistics
by writing 0 (zero) to trans_stat file in devfreq sysfs. An example use
is like following:

echo 0 > /sys/class/devfreq/devfreqX/trans_stat

Signed-off-by: Kamil Konieczny <k.konieczny@samsung.com>
---
Changes in v3:
- add checks for zero in input and clear stats only when zero is written
  to trans_stats
- change documentation of trans_stat in sysfs

Changes in v2:
- instead of creating new sysfs file, add new functionality to trans_stat
  and clear stats when anything is writen to it
---
 Documentation/ABI/testing/sysfs-class-devfreq | 11 +++++---
 drivers/devfreq/devfreq.c                     | 27 ++++++++++++++++++-
 2 files changed, 33 insertions(+), 5 deletions(-)

diff --git a/Documentation/ABI/testing/sysfs-class-devfreq b/Documentation/ABI/testing/sysfs-class-devfreq
index 75897e2fde43..9758eb85ade3 100644
--- a/Documentation/ABI/testing/sysfs-class-devfreq
+++ b/Documentation/ABI/testing/sysfs-class-devfreq
@@ -55,12 +55,15 @@ What:		/sys/class/devfreq/.../trans_stat
 Date:		October 2012
 Contact:	MyungJoo Ham <myungjoo.ham@samsung.com>
 Description:
-		This ABI shows the statistics of devfreq behavior on a
-		specific device. It shows the time spent in each state and
-		the number of transitions between states.
+		This ABI shows or clears the statistics of devfreq behavior
+		on a specific device. It shows the time spent in each state
+		and the number of transitions between states.
 		In order to activate this ABI, the devfreq target device
 		driver should provide the list of available frequencies
-		with its profile.
+		with its profile. If need to reset the statistics of devfreq
+		behavior on a specific device, enter 0(zero) to 'trans_stat'
+		as following:
+			echo 0 > /sys/class/devfreq/.../trans_stat
 
 What:		/sys/class/devfreq/.../userspace/set_freq
 Date:		September 2011
diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
index abecadeb3dc2..218eb64d7f28 100644
--- a/drivers/devfreq/devfreq.c
+++ b/drivers/devfreq/devfreq.c
@@ -1478,7 +1478,32 @@ static ssize_t trans_stat_show(struct device *dev,
 					devfreq->total_trans);
 	return len;
 }
-static DEVICE_ATTR_RO(trans_stat);
+
+static ssize_t trans_stat_store(struct device *dev,
+				struct device_attribute *attr,
+				const char *buf, size_t count)
+{
+	struct devfreq *df = to_devfreq(dev);
+	unsigned int cnt = df->profile->max_state;
+	int err, value;
+
+	if (cnt == 0)
+		return count;
+
+	err = kstrtoint(buf, 10, &value);
+	if (err || value != 0)
+		return count;
+
+	mutex_lock(&df->lock);
+	memset(df->time_in_state, 0, cnt * sizeof(u64));
+	memset(df->trans_table, 0, cnt * cnt * sizeof(int));
+	df->last_stat_updated = get_jiffies_64();
+	df->total_trans = 0;
+	mutex_unlock(&df->lock);
+
+	return count;
+}
+static DEVICE_ATTR_RW(trans_stat);
 
 static struct attribute *devfreq_attrs[] = {
 	&dev_attr_name.attr,
-- 
2.24.0