On 11/12/21 7:35 AM, Ansuel Smith wrote:
diff --git a/Documentation/leds/leds-class.rst b/Documentation/leds/leds-class.rst
index cd155ead8703..e5d266919a19 100644
--- a/Documentation/leds/leds-class.rst
+++ b/Documentation/leds/leds-class.rst
@@ -169,6 +169,38 @@ 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 driven LEDs
+===================================
+
+Some LEDs can be driven by hardware (for example an 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 supported trigger must
+be used.
+
+LED driver should declare the correct control mode supported and should set
+the LED_SOFTWARE_CONTROLLED or LED_HARDWARE_CONTROLLED bit in the flags
+parameter.
+The trigger will check these bits and fail to activate if the control mode
+is not supported. By default if a LED driver doesn't declare a control mode,
if an LED driver
+bit LED_SOFTWARE_CONTROLLED is assumed and set.
+
+The LED must implement 3 main APIs:
+- hw_control_status(): This asks the LED driver if hardware mode is enabled
+ or not.
+- hw_control_start(): This will simply enable the hardware mode for the LED
+ and the LED driver should reset any active blink_mode.
+- hw_control_stop(): This will simply disable the hardware mode for the LED.
+ It's advised to the driver to put the LED in the old state but this is not
+ enforced and putting the LED off is also accepted.
+
+If LED_HARDWARE_CONTROLLED bit is the only control mode set (LED_SOFTWARE_CONTROLLED
+not set) set hw_control_status/start/stop is optional as the LED supports only
^^^ is that an extra "set"? I can't quite read this sentence.
And it would be better with a comma added, like so:
not set),
+hardware mode and any software only trigger will reject activation.
software-only
+
+On init an LED driver that support a hardware mode should reset every blink mode
supports
+set by default.
--
~Randy
