[RFC PATCH v4 2/8] leds: document additional use of blink_set for hardware control

[Ansuel Smith <ansuelsmth@gmail.com>]

blink_set can now be used also to configure blink modes when hardware
control is supported and active.
Trigger will try to use blink_set and a LED driver will use the
trigger_data to configure the blink_modes once blink_set is called.
Setting a brightness to LED_OFF will reset any blink mode and disable
hardware control setting the LED off.

Signed-off-by: Ansuel Smith <ansuelsmth@gmail.com>
---
 Documentation/leds/leds-class.rst | 17 +++++++++++++++++
 drivers/leds/led-class.c          |  7 +++++++
 include/linux/leds.h              |  9 +++++++++
 3 files changed, 33 insertions(+)

diff --git a/Documentation/leds/leds-class.rst b/Documentation/leds/leds-class.rst
index 0175954717a3..c06a18b811de 100644
--- a/Documentation/leds/leds-class.rst
+++ b/Documentation/leds/leds-class.rst
@@ -202,6 +202,23 @@ hardware mode and any software only trigger will reject activation.
 On init a LED driver that support a hardware mode should reset every blink mode
 set by default.
 
+Once a trigger has declared support for hardware-controller blinks, it will use
+blink_set() to try to offload his trigger on activation/configuration.
+blink_set() will return 0 if the requested modes set in trigger_data can be
+controlled by hardware or an error if both the mode bitmap is not supported by
+the hardware or there was a problem in the configuration.
+
+Following blink_set logic, setting brightness to LED_OFF with hardware control active
+will reset any active blink mode and disable hardware control setting the LED to off.
+
+It's in the LED driver's interest to know how to elaborate the trigger data and report support
+for a particular set of blink modes. For this exact reason explicit support for the specific
+trigger is mandatory or the driver returns -EOPNOTSUPP if asked to enter hardware mode
+with a not supported trigger.
+If the driver returns -EOPNOTSUPP on hw_control_configure(), the trigger activation will
+fail as the driver doesn't support that specific hardware blink modes or doesn't know
+how to handle the provided trigger data.
+
 Known Issues
 ============
 
diff --git a/drivers/leds/led-class.c b/drivers/leds/led-class.c
index 98a4dc889344..de39e76a7c6e 100644
--- a/drivers/leds/led-class.c
+++ b/drivers/leds/led-class.c
@@ -180,6 +180,13 @@ static int led_classdev_check_hw_control_functions(struct led_classdev *led_cdev
 	    led_cdev->hw_control_stop))
 		return -EINVAL;
 
+	/* blink_set is mandatory to configure the blink modes
+	 * in hardware control.
+	 */
+	if ((LED_HARDWARE_CONTROLLED & led_cdev->flags) &&
+	    !led_cdev->blink_set)
+		return -EINVAL;
+
 	return 0;
 }
 #endif
diff --git a/include/linux/leds.h b/include/linux/leds.h
index d64e5768e7ab..81d50269a446 100644
--- a/include/linux/leds.h
+++ b/include/linux/leds.h
@@ -76,6 +76,7 @@ struct led_classdev {
 	/* Lower 16 bits reflect status */
 #define LED_SUSPENDED		BIT(0)
 #define LED_UNREGISTERING	BIT(1)
+#define LED_HARDWARE_CONTROL	BIT(2)
 	/* Upper 16 bits reflect control information */
 #define LED_CORE_SUSPENDRESUME	BIT(16)
 #define LED_SYSFS_DISABLE	BIT(17)
@@ -123,6 +124,12 @@ struct led_classdev {
 	 * match the values specified exactly.
 	 * Deactivate blinking again when the brightness is set to LED_OFF
 	 * via the brightness_set() callback.
+	 * With LED_HARDWARE_CONTROL set in LED flags blink_set will also
+	 * configure blink modes requested by the current trigger if
+	 * supported by the LED driver.
+	 * Setting brightness to LED_OFF with hardware control active will
+	 * reset any active blink mode and disable hardware control setting
+	 * the LED off.
 	 */
 	int		(*blink_set)(struct led_classdev *led_cdev,
 				     unsigned long *delay_on,
@@ -166,6 +173,8 @@ struct led_classdev {
 	 */
 	bool			(*hw_control_status)(struct led_classdev *led_cdev);
 	/* Set LED in hardware mode and reset any blink mode active by default.
+	 * A trigger supporting hardware mode will have to use blink_set to configure
+	 * the modes.
 	 */
 	int			(*hw_control_start)(struct led_classdev *led_cdev);
 	/* Disable hardware mode for LED. It's advised to the LED driver to put it to
-- 
2.32.0