PM / devfreq: Add new name attribute for sysfs

The commit 4585fbcb ("PM / devfreq: Modify the device name as devfreq(X) for
sysfs") changed the node name to devfreq(x). After this commit, it is not
possible to get the device name through /sys/class/devfreq/devfreq(X)/*.

Add new name attribute in order to get device name.

Cc: stable@vger.kernel.org
Fixes: 4585fbcb ("PM / devfreq: Modify the device name as devfreq(X) for sysfs")
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>

Documentation/ABI/testing/sysfs-class-devfreq

@@ -7,6 +7,13 @@ Description:
 		The name of devfreq object denoted as ... is same as the
 		name of device using devfreq.
 
+What:		/sys/class/devfreq/.../name
+Date:		November 2019
+Contact:	Chanwoo Choi <cw00.choi@samsung.com>
+Description:
+		The /sys/class/devfreq/.../name shows the name of device
+		of the corresponding devfreq object.
+
 What:		/sys/class/devfreq/.../governor
 Date:		September 2011
 Contact:	MyungJoo Ham <myungjoo.ham@samsung.com>

drivers/devfreq/devfreq.c

@@ -1259,6 +1259,14 @@ int devfreq_remove_governor(struct devfreq_governor *governor)
 }
 EXPORT_SYMBOL(devfreq_remove_governor);
 
+static ssize_t name_show(struct device *dev,
+			struct device_attribute *attr, char *buf)
+{
+	struct devfreq *devfreq = to_devfreq(dev);
+	return sprintf(buf, "%s\n", dev_name(devfreq->dev.parent));
+}
+static DEVICE_ATTR_RO(name);
+
 static ssize_t governor_show(struct device *dev,
 			     struct device_attribute *attr, char *buf)
 {
@@ -1592,6 +1600,7 @@ static ssize_t trans_stat_show(struct device *dev,
 static DEVICE_ATTR_RO(trans_stat);
 
 static struct attribute *devfreq_attrs[] = {
+	&dev_attr_name.attr,
 	&dev_attr_governor.attr,
 	&dev_attr_available_governors.attr,
 	&dev_attr_cur_freq.attr,