[RFC PATCH v2 1/5] leds: trigger: add API for HW offloading of triggers

[Ansuel Smith]

From: Marek Behún <kabel@xxxxxxxxxx>

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.

The second argument to trigger_offload() being false means that the
offloading is being disabled. In this case the function must return 0,
errors are not permitted.

An additional config CONFIG_LEDS_OFFLOAD_TRIGGERS is added to add support
for these special trigger offload driven.

Signed-off-by: Marek Behún <kabel@xxxxxxxxxx>
Signed-off-by: Ansuel Smith <ansuelsmth@xxxxxxxxx>
---
 Documentation/leds/leds-class.rst | 20 +++++++++++++++++++
 drivers/leds/led-triggers.c       |  1 +
 drivers/leds/trigger/Kconfig      | 10 ++++++++++
 include/linux/leds.h              | 33 +++++++++++++++++++++++++++++++
 4 files changed, 64 insertions(+)

diff --git a/Documentation/leds/leds-class.rst b/Documentation/leds/leds-class.rst
index cd155ead8703..5bf6e5d471ce 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 be driven by hardware triggers (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, LED driver must support this and a deficated offload
+trigger must be used. The LED must implement the trigger_offload() method and
+the trigger code must try to call this method (via led_trigger_offload()
+function) to set the LED to this particular mode. (and disable any software
+blinking)
+
+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.
+
+If the second argument (enable) to the trigger_offload() method is false, any
+active HW offloading must be deactivated. In this case errors are not permitted
+in the trigger_offload() method and the driver will be set to the new trigger.
 
 Known Issues
 ============
diff --git a/drivers/leds/led-triggers.c b/drivers/leds/led-triggers.c
index 072491d3e17b..281c52914f42 100644
--- a/drivers/leds/led-triggers.c
+++ b/drivers/leds/led-triggers.c
@@ -179,6 +179,7 @@ int led_trigger_set(struct led_classdev *led_cdev, struct led_trigger *trig)
 
 		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/drivers/leds/trigger/Kconfig b/drivers/leds/trigger/Kconfig
index dc6816d36d06..33aba8defeab 100644
--- a/drivers/leds/trigger/Kconfig
+++ b/drivers/leds/trigger/Kconfig
@@ -9,6 +9,16 @@ menuconfig LEDS_TRIGGERS
 
 if LEDS_TRIGGERS
 
+config LEDS_OFFLOAD_TRIGGERS
+	bool "LED Offload Trigger support"
+	help
+	  This option enabled offload triggers support used by leds that
+	  can be driven in hardware by declaring some specific triggers.
+	  A offload trigger will expose a sysfs dir to configure the
+	  different blinking trigger and the available hardware triggers.
+
+	  If unsure, say Y.
+
 config LEDS_TRIGGER_TIMER
 	tristate "LED Timer Trigger"
 	help
diff --git a/include/linux/leds.h b/include/linux/leds.h
index ba4861ec73d3..949ab461287f 100644
--- a/include/linux/leds.h
+++ b/include/linux/leds.h
@@ -154,6 +154,13 @@ struct led_classdev {
 
 	/* LEDs that have private triggers have this set */
 	struct led_hw_trigger_type	*trigger_type;
+
+#ifdef CONFIG_LEDS_OFFLOAD_TRIGGERS
+	int			offloaded;
+	/* some LEDs cne be driven by HW */
+	int			(*trigger_offload)(struct led_classdev *led_cdev,
+						   bool enable);
+#endif
 #endif
 
 #ifdef CONFIG_LEDS_BRIGHTNESS_HW_CHANGED
@@ -409,6 +416,32 @@ static inline void *led_get_trigger_data(struct led_classdev *led_cdev)
 	return led_cdev->trigger_data;
 }
 
+#ifdef CONFIG_LEDS_OFFLOAD_TRIGGERS
+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_cdev->offloaded = false;
+	}
+}
+#endif
+
 /**
  * led_trigger_rename_static - rename a trigger
  * @name: the new trigger name
-- 
2.32.0