leds: triggers: add device attribute support

As many triggers use device attributes, add support for these in
led_trigger_set which allows simplifying the drivers accordingly.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Jacek Anaszewski <jacek.anaszewski@gmail.com>
diff --git a/include/linux/leds.h b/include/linux/leds.h
index ba5baaa..33484a5 100644
--- a/include/linux/leds.h
+++ b/include/linux/leds.h
@@ -262,8 +262,19 @@
 
 	/* Link to next registered trigger */
 	struct list_head  next_trig;
+
+	const struct attribute_group **groups;
 };
 
+/*
+ * Currently the attributes in struct led_trigger::groups are added directly to
+ * the LED device. As this might change in the future, the following
+ * macros abstract getting the LED device and its trigger_data from the dev
+ * parameter passed to the attribute accessor functions.
+ */
+#define led_trigger_get_led(dev)	((struct led_classdev *)dev_get_drvdata((dev)))
+#define led_trigger_get_drvdata(dev)	(led_get_trigger_data(led_trigger_get_led(dev)))
+
 ssize_t led_trigger_store(struct device *dev, struct device_attribute *attr,
 			const char *buf, size_t count);
 ssize_t led_trigger_show(struct device *dev, struct device_attribute *attr,