[PATCH RFC leds + net-next 3/7] leds: trigger: add API for HW offloading of triggers

["Marek Behún" <kabel@kernel.org>]

Add method trigger_offload() and member variable `offloaded` to struct
led_classdev. Add helper functions led_trigger_offload() and
led_trigger_offload_stop().

The trigger_offload() method, when implemented by the LED driver, should
be called (via led_trigger_offload() function) from trigger code wanting
to be offloaded at the moment when configuration of the trigger changes.

If the trigger is successfully offloaded, this method returns 0 and the
trigger does not have to blink the LED in software.

If the trigger with given configuration cannot be offloaded, the method
should return -EOPNOTSUPP, in which case the trigger must blink the LED
in SW.

Signed-off-by: Marek Behún <kabel@kernel.org>
---
 Documentation/leds/leds-class.rst | 20 ++++++++++++++++++++
 drivers/leds/led-triggers.c       |  1 +
 include/linux/leds.h              | 27 +++++++++++++++++++++++++++
 3 files changed, 48 insertions(+)

diff --git a/Documentation/leds/leds-class.rst b/Documentation/leds/leds-class.rst
index a0708d3f3d0b..45360ff99f8d 100644
--- a/Documentation/leds/leds-class.rst
+++ b/Documentation/leds/leds-class.rst
@@ -169,6 +169,26 @@ Setting the brightness to zero with brightness_set() callback function
 should completely turn off the LED and cancel the previously programmed
 hardware blinking function, if any.
 
+Hardware offloading of LED triggers
+===================================
+
+Some LEDs can offload SW triggers to hardware (for example a LED connected to
+an ethernet PHY or an ethernet switch can be configured to blink on activity on
+the network, which in software is done by the netdev trigger).
+
+To do such offloading, both the trigger code and LED driver must support this.
+The LED must implement the trigger_offload() method and the trigger code must
+try to call this method (via led_trigger_offload() function) when configuration
+of the trigger (trigger_data) changes.
+
+The implementation of the trigger_offload() method by the LED driver must return
+0 if the offload is successful and -EOPNOTSUPP if the requested trigger
+configuration is not supported and the trigger should be executed in software.
+If trigger_offload() returns negative value, the trigger will be done in
+software, so any active offloading must also be disabled.
+
+If the second argument (enable) to the trigger_offload() method is false, any
+active HW offloading must be deactivated.
 
 Known Issues
 ============
diff --git a/drivers/leds/led-triggers.c b/drivers/leds/led-triggers.c
index 91da90cfb11d..9056a66f4661 100644
--- a/drivers/leds/led-triggers.c
+++ b/drivers/leds/led-triggers.c
@@ -177,6 +177,7 @@ int led_trigger_set(struct led_classdev *led_cdev, struct led_trigger *trig)
 			flags);
 		cancel_work_sync(&led_cdev->set_brightness_work);
 		led_stop_software_blink(led_cdev);
+		led_trigger_offload_stop(led_cdev);
 		if (led_cdev->trigger->deactivate)
 			led_cdev->trigger->deactivate(led_cdev);
 		device_remove_groups(led_cdev->dev, led_cdev->trigger->groups);
diff --git a/include/linux/leds.h b/include/linux/leds.h
index 6a8d6409c993..d7e17f1d6f3c 100644
--- a/include/linux/leds.h
+++ b/include/linux/leds.h
@@ -148,6 +148,11 @@ struct led_classdev {
 
 	/* LEDs that have private triggers have this set */
 	struct led_hw_trigger_type	*trigger_type;
+
+	/* some LEDs may be able to offload some SW triggers to HW */
+	int		(*trigger_offload)(struct led_classdev *led_cdev,
+					   bool enable);
+	bool			offloaded;
 #endif
 
 #ifdef CONFIG_LEDS_BRIGHTNESS_HW_CHANGED
@@ -405,6 +410,28 @@ static inline void *led_get_trigger_data(struct led_classdev *led_cdev)
 	return led_cdev->trigger_data;
 }
 
+static inline int led_trigger_offload(struct led_classdev *led_cdev)
+{
+	int ret;
+
+	if (!led_cdev->trigger_offload)
+		return -EOPNOTSUPP;
+
+	ret = led_cdev->trigger_offload(led_cdev, true);
+	led_cdev->offloaded = !ret;
+
+	return ret;
+}
+
+static inline void led_trigger_offload_stop(struct led_classdev *led_cdev)
+{
+	if (!led_cdev->trigger_offload)
+		return;
+
+	if (led_cdev->offloaded)
+		led_cdev->trigger_offload(led_cdev, false);
+}
+
 /**
  * led_trigger_rename_static - rename a trigger
  * @name: the new trigger name
-- 
2.26.2