linux-kernel - [linux-next PATCH 6/7] PM / devfreq: allow sysfs governor node to switch governor

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Date:	Mon, 29 Oct 2012 15:01:47 -0500
From:	Nishanth Menon <nm@...com>
To:	linux-pm <linux-pm@...r.kernel.org>
CC:	Nishanth Menon <nm@...com>,
	Rajagopal Venkat <rajagopal.venkat@...aro.org>,
	MyungJoo Ham <myungjoo.ham@...sung.com>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>, Kevin Hilman <khilman@...com>,
	<linux-kernel@...r.kernel.org>
Subject: [linux-next PATCH 6/7] PM / devfreq: allow sysfs governor node to switch governor

This allows us to select governor runtime from the
default configuration without having to rebuild kernel
or the devfreq driver using the sysfs node:
/sys/class/devfreq/.../governor
cat of the governor will return valid governor
and an echo 'governor_name'>governor will switch
governor

Cc: Rajagopal Venkat <rajagopal.venkat@...aro.org>
Cc: MyungJoo Ham <myungjoo.ham@...sung.com>
Cc: Kyungmin Park <kyungmin.park@...sung.com>
Cc: "Rafael J. Wysocki" <rjw@...k.pl>
Cc: Kevin Hilman <khilman@...com>
Cc: linux-pm@...r.kernel.org
Cc: linux-kernel@...r.kernel.org

Signed-off-by: Nishanth Menon <nm@...com>
---
 Documentation/ABI/testing/sysfs-class-devfreq |    2 +-
 drivers/devfreq/devfreq.c                     |   40 ++++++++++++++++++++++++-
 2 files changed, 40 insertions(+), 2 deletions(-)

diff --git a/Documentation/ABI/testing/sysfs-class-devfreq b/Documentation/ABI/testing/sysfs-class-devfreq
index e672ccb..293f6b2 100644
--- a/Documentation/ABI/testing/sysfs-class-devfreq
+++ b/Documentation/ABI/testing/sysfs-class-devfreq
@@ -11,7 +11,7 @@ What:		/sys/class/devfreq/.../governor
 Date:		September 2011
 Contact:	MyungJoo Ham <myungjoo.ham@...sung.com>
 Description:
-		The /sys/class/devfreq/.../governor shows the name of the
+		The /sys/class/devfreq/.../governor show or set the name of the
 		governor used by the corresponding devfreq object.
 
 What:		/sys/class/devfreq/.../cur_freq
diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
index bd96e32..8535f8c 100644
--- a/drivers/devfreq/devfreq.c
+++ b/drivers/devfreq/devfreq.c
@@ -629,6 +629,44 @@ static ssize_t show_governor(struct device *dev,
 	return sprintf(buf, "%s\n", to_devfreq(dev)->governor->name);
 }
 
+static ssize_t store_governor(struct device *dev, struct device_attribute *attr,
+			      const char *buf, size_t count)
+{
+	struct devfreq *df = to_devfreq(dev);
+	int ret = 0;
+	struct devfreq_governor *governor;
+
+	mutex_lock(&devfreq_list_lock);
+	governor = find_devfreq_governor(buf);
+	if (IS_ERR(governor)) {
+		ret = PTR_ERR(governor);
+		goto out;
+	}
+	if (df->governor == governor)
+		goto out;
+
+	if (df->governor) {
+		ret = df->governor->event_handler(df, DEVFREQ_GOV_STOP, NULL);
+		if (ret) {
+			dev_warn(dev, "%s: Governor %s not stopped(%d)\n",
+				 __func__, df->governor->name, ret);
+			goto out;
+		}
+	}
+	df->governor = governor;
+	strncpy(df->governor_name, governor->name, DEVFREQ_NAME_LEN);
+	ret = df->governor->event_handler(df, DEVFREQ_GOV_START, NULL);
+	if (ret)
+		dev_warn(dev, "%s: Governor %s not started(%d)\n",
+			 __func__, df->governor->name, ret);
+out:
+	mutex_unlock(&devfreq_list_lock);
+
+	if (!ret)
+		ret = count;
+	return ret;
+}
+
 static ssize_t show_freq(struct device *dev,
 			 struct device_attribute *attr, char *buf)
 {
@@ -773,7 +811,7 @@ static ssize_t show_available_freqs(struct device *d,
 }
 
 static struct device_attribute devfreq_attrs[] = {
-	__ATTR(governor, S_IRUGO, show_governor, NULL),
+	__ATTR(governor, S_IRUGO | S_IWUSR, show_governor, store_governor),
 	__ATTR(cur_freq, S_IRUGO, show_freq, NULL),
 	__ATTR(available_frequencies, S_IRUGO, show_available_freqs, NULL),
 	__ATTR(target_freq, S_IRUGO, show_target_freq, NULL),
-- 
1.7.9.5

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