[PATCH -next 2/2] leds: add /sys/class/leds/<led>/current-trigger

[Akinobu Mita <akinobu.mita@gmail.com>]

Reading /sys/class/leds/<led>/trigger returns all available LED triggers.
However, this violates the "one value per file" rule of sysfs.

This provides /sys/class/leds/<led>/current-trigger which is almost
identical to /sys/class/leds/<led>/trigger.  The only difference is that
'current-trigger' only shows the current trigger name.

This new file follows the "one value per file" rule of sysfs.
We can find all available LED triggers by listing the
/sys/devices/virtual/led-trigger/ directory.

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Jacek Anaszewski <jacek.anaszewski@gmail.com>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: Dan Murphy <dmurphy@ti.com>
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
---
 Documentation/ABI/testing/sysfs-class-led | 13 +++++++++++
 drivers/leds/led-class.c                  | 10 ++++++++
 drivers/leds/led-triggers.c               | 38 +++++++++++++++++++++++++++----
 drivers/leds/leds.h                       |  5 ++++
 4 files changed, 62 insertions(+), 4 deletions(-)

diff --git a/Documentation/ABI/testing/sysfs-class-led b/Documentation/ABI/testing/sysfs-class-led
index 5f67f7a..fdfed3f 100644
--- a/Documentation/ABI/testing/sysfs-class-led
+++ b/Documentation/ABI/testing/sysfs-class-led
@@ -61,3 +61,16 @@ Description:
 		gpio and backlight triggers. In case of the backlight trigger,
 		it is useful when driving a LED which is intended to indicate
 		a device in a standby like state.
+
+What:		/sys/class/leds/<led>/current-trigger
+Date:		September 2019
+KernelVersion:	5.5
+Contact:	linux-leds@vger.kernel.org
+Description:
+		Set the trigger for this LED. A trigger is a kernel based source
+		of LED events.
+		Writing the trigger name to this file will change the current
+		trigger. Trigger specific parameters can appear in
+		/sys/class/leds/<led> once a given trigger is selected. For
+		their documentation see sysfs-class-led-trigger-*.
+		Reading this file will return the current LED trigger name.
diff --git a/drivers/leds/led-class.c b/drivers/leds/led-class.c
index 3f04334..3cb0d8a 100644
--- a/drivers/leds/led-class.c
+++ b/drivers/leds/led-class.c
@@ -74,12 +74,22 @@ static ssize_t max_brightness_show(struct device *dev,
 static DEVICE_ATTR_RO(max_brightness);
 
 #ifdef CONFIG_LEDS_TRIGGERS
+
+static DEVICE_ATTR(current_trigger, 0644, led_current_trigger_show,
+		   led_current_trigger_store);
+
+static struct attribute *led_current_trigger_attrs[] = {
+	&dev_attr_current_trigger.attr,
+	NULL,
+};
+
 static BIN_ATTR(trigger, 0644, led_trigger_read, led_trigger_write, 0);
 static struct bin_attribute *led_trigger_bin_attrs[] = {
 	&bin_attr_trigger,
 	NULL,
 };
 static const struct attribute_group led_trigger_group = {
+	.attrs = led_current_trigger_attrs,
 	.bin_attrs = led_trigger_bin_attrs,
 };
 #endif
diff --git a/drivers/leds/led-triggers.c b/drivers/leds/led-triggers.c
index 0b810cf..a2ef674 100644
--- a/drivers/leds/led-triggers.c
+++ b/drivers/leds/led-triggers.c
@@ -27,11 +27,9 @@ LIST_HEAD(trigger_list);
 
  /* Used by LED Class */
 
-ssize_t led_trigger_write(struct file *filp, struct kobject *kobj,
-			  struct bin_attribute *bin_attr, char *buf,
-			  loff_t pos, size_t count)
+static ssize_t led_trigger_store(struct device *dev, const char *buf,
+				 size_t count)
 {
-	struct device *dev = kobj_to_dev(kobj);
 	struct led_classdev *led_cdev = dev_get_drvdata(dev);
 	struct led_trigger *trig;
 	int ret = count;
@@ -67,8 +65,25 @@ ssize_t led_trigger_write(struct file *filp, struct kobject *kobj,
 	mutex_unlock(&led_cdev->led_access);
 	return ret;
 }
+
+ssize_t led_trigger_write(struct file *filp, struct kobject *kobj,
+			  struct bin_attribute *bin_attr, char *buf,
+			  loff_t pos, size_t count)
+{
+	struct device *dev = kobj_to_dev(kobj);
+
+	return led_trigger_store(dev, buf, count);
+}
 EXPORT_SYMBOL_GPL(led_trigger_write);
 
+ssize_t led_current_trigger_store(struct device *dev,
+				struct device_attribute *attr, const char *buf,
+				size_t count)
+{
+	return led_trigger_store(dev, buf, count);
+}
+EXPORT_SYMBOL_GPL(led_current_trigger_store);
+
 __printf(3, 4)
 static int led_trigger_snprintf(char *buf, ssize_t size, const char *fmt, ...)
 {
@@ -144,6 +159,21 @@ ssize_t led_trigger_read(struct file *filp, struct kobject *kobj,
 }
 EXPORT_SYMBOL_GPL(led_trigger_read);
 
+ssize_t led_current_trigger_show(struct device *dev,
+				 struct device_attribute *attr, char *buf)
+{
+	struct led_classdev *led_cdev = dev_get_drvdata(dev);
+	int len;
+
+	down_read(&led_cdev->trigger_lock);
+	len = scnprintf(buf, PAGE_SIZE, "%s\n", led_cdev->trigger ?
+			led_cdev->trigger->name : "none");
+	up_read(&led_cdev->trigger_lock);
+
+	return len;
+}
+EXPORT_SYMBOL_GPL(led_current_trigger_show);
+
 /* Caller must ensure led_cdev->trigger_lock held */
 int led_trigger_set(struct led_classdev *led_cdev, struct led_trigger *trig)
 {
diff --git a/drivers/leds/leds.h b/drivers/leds/leds.h
index 2d9eb48..c581690 100644
--- a/drivers/leds/leds.h
+++ b/drivers/leds/leds.h
@@ -29,6 +29,11 @@ ssize_t led_trigger_read(struct file *filp, struct kobject *kobj,
 ssize_t led_trigger_write(struct file *filp, struct kobject *kobj,
 			struct bin_attribute *bin_attr, char *buf,
 			loff_t pos, size_t count);
+ssize_t led_current_trigger_store(struct device *dev,
+				struct device_attribute *attr,
+				const char *buf, size_t count);
+ssize_t led_current_trigger_show(struct device *dev,
+				struct device_attribute *attr, char *buf);
 
 extern struct rw_semaphore leds_list_lock;
 extern struct list_head leds_list;
-- 
2.7.4