leds: add APIs for LEDs hw control

Add an option to permit LED driver to declare support for a specific
trigger to use hw control and setup the LED to blink based on specific
provided modes.

Add APIs for LEDs hw control. These functions will be used to activate
hardware control where a LED will use the provided flags, from an
unique defined supported trigger, to setup the LED to be driven by
hardware.

Add hw_control_is_supported() to ask the LED driver if the requested
mode by the trigger are supported and the LED can be setup to follow
the requested modes.

Deactivate hardware blink control by setting brightness to LED_OFF via
the brightness_set() callback.

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/leds.h

@@ -183,6 +183,43 @@ struct led_classdev {
 
 	/* LEDs that have private triggers have this set */
 	struct led_hw_trigger_type	*trigger_type;
+
+	/* Unique trigger name supported by LED set in hw control mode */
+	const char		*hw_control_trigger;
+	/*
+	 * Check if the LED driver supports the requested mode provided by the
+	 * defined supported trigger to setup the LED to hw control mode.
+	 *
+	 * Return 0 on success. Return -EOPNOTSUPP when the passed flags are not
+	 * supported and software fallback needs to be used.
+	 * Return a negative error number on any other case  for check fail due
+	 * to various reason like device not ready or timeouts.
+	 */
+	int			(*hw_control_is_supported)(struct led_classdev *led_cdev,
+							   unsigned long flags);
+	/*
+	 * Activate hardware control, LED driver will use the provided flags
+	 * from the supported trigger and setup the LED to be driven by hardware
+	 * following the requested mode from the trigger flags.
+	 * Deactivate hardware blink control by setting brightness to LED_OFF via
+	 * the brightness_set() callback.
+	 *
+	 * Return 0 on success, a negative error number on flags apply fail.
+	 */
+	int			(*hw_control_set)(struct led_classdev *led_cdev,
+						  unsigned long flags);
+	/*
+	 * Get from the LED driver the current mode that the LED is set in hw
+	 * control mode and put them in flags.
+	 * Trigger can use this to get the initial state of a LED already set in
+	 * hardware blink control.
+	 *
+	 * Return 0 on success, a negative error number on failing parsing the
+	 * initial mode. Error from this function is NOT FATAL as the device
+	 * may be in a not supported initial state by the attached LED trigger.
+	 */
+	int			(*hw_control_get)(struct led_classdev *led_cdev,
+						  unsigned long *flags);
 #endif
 
 #ifdef CONFIG_LEDS_BRIGHTNESS_HW_CHANGED