Re: [PATCH v3] leds: Introduce userspace leds driver

From: David Lechner
Date: Fri Sep 16 2016 - 11:32:27 EST

On 09/16/2016 12:59 AM, Pavel Machek wrote:

+The current brightness is found by reading a single byte from the
+device. Values are unsigned: 0 to 255. Reading does not block and
always returns
+the most recent brightness value. The device node can also be polled
to notify
+when the brightness value changes.

What is going on there? We have O_NONBLOCK, user should be able to
select if he wants blocking behaviour or not.

I will look into this.

And yes, there's interface for creating a LED, but not one for
deleting it?

uleds.txt says "The LED class device will be removed when the open file handle to /dev/uleds is closed."

Is this not clear?

And... how is it going to work with multiple LEDs? Userspace gets
single bytes with brightness. How does it know to which LED the
brightness belongs?

It looks like this is missing from uleds.txt. By opening multiple file handles to /dev/uleds, you can create multiple devices. Each file handle will return a different value when read that corresponds to the LEDs class device that belongs to it.