[RFC PATCH 1/6] leds: trigger: add API for HW offloading of triggers

Ansuel Smith
2021-11-07T17:58:11Z

From: 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.

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@kernel.org>
Signed-off-by: Ansuel Smith <ansuelsmth@gmail.com>
---
Documentation/leds/leds-class.rst | 22 +++++++++++++++++++++
drivers/leds/led-triggers.c | 1 +
drivers/leds/trigger/Kconfig | 10 ++++++++++
include/linux/leds.h | 33 +++++++++++++++++++++++++++++++
4 files changed, 66 insertions(+)

diff --git a/Documentation/leds/leds-class.rst b/Documentation/leds/leds-class.rst
index cd155ead8703..035a738afc4a 100644
--- a/Documentation/leds/leds-class.rst
+++ b/Documentation/leds/leds-class.rst
@@ -169,6 +169,28 @@ 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, LED driver must support the 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) 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 triggering 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. In this case errors are not permitted
+in the trigger_offload() method.
+

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..c073e64e0a37 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 HW by declaring some specific triggers.
+ A offload trigger will expose a sysfs dir to configure the
+ different blinking trigger and the available hw trigger.
+
+ 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