[PATCH] leds: Add documentation about possible subsystem improvements

[Pavel Machek <pavel@ucw.cz>]

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commit f91fdbb47959537df6175cb4f0e6eb75757540f7
Author: Pavel Machek <pavel@ucw.cz>
Date:   Fri Sep 25 11:29:17 2020 +0200

    leds: Add documentation about possible subsystem improvements
    
    Help welcome :-).
    
    Signed-off-by: Pavel Machek <pavel@ucw.cz>

diff --git a/drivers/leds/TODO b/drivers/leds/TODO
new file mode 100644
index 000000000000..5beaca261f0a
--- /dev/null
+++ b/drivers/leds/TODO
@@ -0,0 +1,58 @@
+-*- org -*-
+
+* On/off LEDs should have max_brightness of 1
+* Get rid of enum led_brightness
+
+It is really an integer, as maximum is configurable. Get rid of it, or
+make it into typedef or something.
+
+* Review atomicity requirements in LED subsystem
+
+Calls that may and that may not block are mixed in same structure, and
+semantics is sometimes non-intuitive. (For example blink callback may
+not sleep.) Review the requirements for any bugs and document them
+clearly.
+
+* LED names are still a mess
+
+No two LEDs have same name, so the names are probably unusable for the
+userland. Nudge authors into creating common LED names for common
+functionality.
+
+? Perhaps check for known LED names during boot, and warn if there are
+LEDs not on the list?
+
+* Split drivers into subdirectories
+
+The number of drivers is getting big, and driver for on/off LED on a
+i/o port is really quite different from camera flash LED, which is
+really different from driver for RGB color LED that can run its own
+microcode. Split the drivers somehow.
+
+* Figure out what to do with RGB leds
+
+Multicolor is a bit too abstract. Yes, we can have
+Green-Magenta-Ultraviolet LED, but so far all the LEDs we support are
+RGB, and not even RGB-White or RGB-Yellow variants emerged.
+
+Multicolor is not a good fit for RGB LED. It does not really know
+about LED color.  In particular, there's no way to make LED "white".
+
+Userspace is interested in knowing "this LED can produce arbitrary
+color", which not all multicolor LEDs can.
+
+	Proposal: let's add "rgb" to led_colors in drivers/leds/led-core.c,
+	add corresponding device tree defines, and use that, instead of
+	multicolor for RGB LEDs.
+
+	We really need to do that now; "white" stuff can wait.
+
+RGB LEDs are quite common, and it would be good to be able to turn LED
+white and to turn it into any arbitrary color. It is essential that
+userspace is able to set arbitrary colors, and it might be good to
+have that ability from kernel, too... to allow full-color triggers.
+
+* Command line utility to manipulate the LEDs?
+
+/sys interface is not really suitable to use by hand, should we have
+an utility to perform LED control?


-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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