leds: trigger: netdev: Implement hw_offloaded() callback

"netdev" can run in hardware control according to hardware capabilities
and trigger options.

Implement hw_offloaded() callback to provide its hardware control state
to the LED core, and document the relation between the custom
"offloaded" attribute and the generic "trigger_may_offload_to_hw"
attribute.

The callback mimics how the existing "offloaded" attribute does, i.e.,
locklessly reads hw_control, as it's just a hint and don't need to be
accurate.

Acked-by: Ike Panhc <ikepanhc@gmail.com>
Signed-off-by: Rong Zhang <i@rong.moe>
Link: https://patch.msgid.link/20260921-leds-trigger-hw-changed-v7-8-fe3cdb6dec51@rong.moe
Signed-off-by: Lee Jones <lee@kernel.org>

Documentation/ABI/testing/sysfs-class-led

@@ -101,6 +101,9 @@ Description:
 		- `[foo_trigger]`: the trigger is selected and offloaded to
 		  hardware.
 
+		The "netdev" trigger also provides a custom attribute to
+		indicate its state, see `/sys/class/leds/<led>/offloaded`.
+
 What:		/sys/class/leds/<led>/inverted
 Date:		January 2011
 KernelVersion:	2.6.38

Documentation/ABI/testing/sysfs-class-led-trigger-netdev

@@ -75,6 +75,9 @@ Description:
 		If 1, the LED blinking in requested mode is offloaded to
 		hardware.
 
+		LED trigger core also provides a generic attribute for this
+		purpose, see `/sys/class/leds/<led>/trigger_may_offload_to_hw`.
+
 What:		/sys/class/leds/<led>/link_10
 Date:		Jun 2023
 KernelVersion:	6.5

drivers/leds/trigger/ledtrig-netdev.c

@@ -795,10 +795,18 @@ static void netdev_trig_deactivate(struct led_classdev *led_cdev)
 	kfree(trigger_data);
 }
 
+static bool netdev_trig_hw_offloaded(struct led_classdev *led_cdev)
+{
+	struct led_netdev_data *trigger_data = led_get_trigger_data(led_cdev);
+
+	return trigger_data->hw_control;
+}
+
 static struct led_trigger netdev_led_trigger = {
 	.name = "netdev",
 	.activate = netdev_trig_activate,
 	.deactivate = netdev_trig_deactivate,
+	.hw_offloaded = netdev_trig_hw_offloaded,
 	.groups = netdev_trig_groups,
 };