On Tue, Nov 09, 2021 at 03:26:01AM +0100, Ansuel Smith wrote:

Some LEDs can be driven by 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 this and a supported
trigger must be used.

LED driver should declare the correct blink_mode supported and should set
the blink_mode parameter to one of HARDWARE_CONTROLLED or
SOFTWARE_HARDWARE_CONTROLLED.
The trigger will check this option and fail to activate if the blink_mode
is not supported. By default if a LED driver doesn't declare blink_mode,
SOFTWARE_CONTROLLED is assumed.

The LED must implement 3 main API:
- trigger_offload_status(): This asks the LED driver if offload mode is
    enabled or not.
    Triggers will check if the offload mode is supported and will be
    activated accordingly. If the trigger can't run in software mode,
    return -EOPNOTSUPP as the blinking can't be simulated by software.

I don't understand this last part. The LED controller is not
implementing software mode, other than providing a method to manually
turn the LED on and off. And there is a well defined call for that. If
that call is a NULL, it is clear it is not implemented. There is no
need to ask the driver.

     Andrew