Re: [PATCH 2/2] leds: lp5024: Add the LP5024/18 RGB LED driver

From: Jacek Anaszewski
Date: Sun Jan 13 2019 - 11:37:14 EST

Hi Vesa,

On 1/9/19 7:46 AM, Vesa JÃÃskelÃinen wrote:
Hi Jacek,

On 07/01/2019 23.13, Jacek Anaszewski wrote:
Hi Vesa,

On 1/5/19 1:39 AM, Vesa JÃÃskelÃinen wrote:
Hi Jacek,

On 04/01/2019 23.37, Jacek Anaszewski wrote:
But, aside from that hypothetic issue, we need a solution for
LEDn_BRIGHTNESS feature of lp5024, i.e. setting color intensity
via a single register write. How would you propose to address that?

You could model it to something like this in device tree:

led-module @ <i2c-address> {
ÂÂÂÂÂcompatible = "lp5024";

ÂÂÂÂÂ// There is in hardware setup to use either linear or
ÂÂÂÂÂ// logarithmic scaling:
ÂÂÂÂÂ//enable-logarithmic-brightness;

ÂÂÂÂÂled0 {
ÂÂÂÂÂÂÂÂ // this will create led instance for LED0 in lp5024
ÂÂÂÂÂÂÂÂ label = "lp-led0";

ÂÂÂÂÂÂÂÂ // This specifies LED number within lp5024
ÂÂÂÂÂÂÂÂ led-index = <0>;ÂÂ // set output-base as 0*3 == 0

ÂÂÂÂÂÂÂÂ element-red {
ÂÂÂÂÂÂÂÂÂÂÂÂ // refers to OUT0
ÂÂÂÂÂÂÂÂÂÂÂÂ output-offset = <0>;
ÂÂÂÂÂÂÂÂ };

ÂÂÂÂÂÂÂÂ element-green {
ÂÂÂÂÂÂÂÂÂÂÂÂ // refers to OUT1
ÂÂÂÂÂÂÂÂÂÂÂÂ output-offset = <1>;
ÂÂÂÂÂÂÂÂ };

ÂÂÂÂÂÂÂÂ element-blue {
ÂÂÂÂÂÂÂÂÂÂÂÂ // refers to OUT2
ÂÂÂÂÂÂÂÂÂÂÂÂ output-offset = <2>;
ÂÂÂÂÂÂÂÂ };

ÂÂÂÂÂ};

ÂÂÂÂÂled1 {
ÂÂÂÂÂÂÂÂ // this will create led instance for LED1 in lp5024
ÂÂÂÂÂÂÂÂ label = "lp-led1";

ÂÂÂÂÂÂÂÂ // This specifies LED number within lp5024
ÂÂÂÂÂÂÂÂ led-index = <1>;ÂÂ // set output-base as 1*3 == 3

ÂÂÂÂÂÂÂÂ element-red {
ÂÂÂÂÂÂÂÂÂÂÂÂ // refers to OUT3
ÂÂÂÂÂÂÂÂÂÂÂÂ output-offset = <0>;
ÂÂÂÂÂÂÂÂ };

ÂÂÂÂÂÂÂÂ element-green {
ÂÂÂÂÂÂÂÂÂÂÂÂ // refers to OUT4
ÂÂÂÂÂÂÂÂÂÂÂÂ output-offset = <1>;
ÂÂÂÂÂÂÂÂ };

ÂÂÂÂÂÂÂÂ element-blue {
ÂÂÂÂÂÂÂÂÂÂÂÂ // refers to OUT5
ÂÂÂÂÂÂÂÂÂÂÂÂ output-offset = <2>;
ÂÂÂÂÂÂÂÂ };

ÂÂÂÂÂ};

ÂÂÂÂÂbank-led {
ÂÂÂÂÂÂÂÂ // this will create led instance for bank leds in lp5024
ÂÂÂÂÂÂÂÂ label = "lp-bank-led";

ÂÂÂÂÂÂÂÂ // configured bank led configuration
ÂÂÂÂÂÂÂÂ led-index = <2 3 4 5 6 7>;
ÂÂÂÂÂÂÂÂ // As here is list of led-indices this entry is
ÂÂÂÂÂÂÂÂ // assumed to be bank configuration. Bank mode is enable
ÂÂÂÂÂÂÂÂ // for the indices.

ÂÂÂÂÂÂÂÂ // set output-base as BANK A

ÂÂÂÂÂÂÂÂ element-red {
ÂÂÂÂÂÂÂÂÂÂÂÂ // refers to BANK A
ÂÂÂÂÂÂÂÂÂÂÂÂ output-offset = <0>;
ÂÂÂÂÂÂÂÂ };

ÂÂÂÂÂÂÂÂ element-green {
ÂÂÂÂÂÂÂÂÂÂÂÂ // refers to BANK B
ÂÂÂÂÂÂÂÂÂÂÂÂ output-offset = <1>;
ÂÂÂÂÂÂÂÂ };

ÂÂÂÂÂÂÂÂ element-blue {
ÂÂÂÂÂÂÂÂÂÂÂÂ // refers to BANK C
ÂÂÂÂÂÂÂÂÂÂÂÂ output-offset = <2>;
ÂÂÂÂÂÂÂÂ };
ÂÂÂÂÂ};
};

This would then create three led instances and each led instance has brightness setting and that goes straight to hardware.

If one would want to override hardware control for brightness then I suppose you would define in led node something like:

ÂÂÂÂÂbrightness-model = "hsl"

This would then pick red, green and blue elements for hsl calculations and others color elements for linear. LED specific hardware brightness would then be either 0 or 0xFF depending if all of LED color elements are zero or not.

Would that kind of model work?

I'd prefer to have single RGB LED device. And your DT design
is unnecessarily complex and a bit confusing.

As this chip series is kinda designed for N x RGB LED's my idea was that if from user space point of view we model it as N times of individual RGB LED instances that may not even have anything to do with together. Eg. could be used for different purposes and such.

Actually the only differences between your DT design and that
initially proposed by Dan are element-* nodes describing
IOUT -> color mapping.

I am not sure if LEDn_BRIGHTNESS feature would work as intended
when colors are not assigned to IOUTs in the order shown on the
Figure 14. in the data sheet. I'm afraid that we would be changing
hue as well (sticking to the HSV nomenclature). Let's not bother with
covering arrangements not being in line with the data sheet
recommendations.

Of course the element-color nodes will be necessary for leds-pwm,
like in your github example.

And in device tree one would define logical connections for the leds so they would be mapped logically correct to user space.

If one would define it like:

led1 {
ÂÂÂÂ// this will create led instance for LED1 in lp5024
ÂÂÂÂlabel = "lp-led1";

ÂÂÂÂ// This specifies LED number within lp5024
ÂÂÂÂled-sources = <1>;
};
(note changed led-index to led-sources as that is what Pavel had and preferred)

We could assume that it is RGB led in this driver's case and create it automatically with elements "red", "green", and "blue". And this could then be mapped automatically to HSL color elements or what ever the model would be.

If you would model it differently in your hardware design then you would need to define more device tree nodes. Eg. if your order of LEDs would not be red, green, blue. Or if you would have non-RGB led(s) in there.

Also, you provided scarce information about sysfs interface.
It would be nice to see the sequence of commands.

In this case it could be:

# Note: Updated color to value array model.

$ ls /sys/class/leds
lp-led0ÂÂÂ lp-led1ÂÂÂ lp-bank-led

$ ls /sys/class/leds/lp-led0
brightnessÂÂÂ color

$ ls /sys/class/leds/lp-led1
brightnessÂÂÂ color

$ ls /sys/class/leds/lp-bank-led
brightnessÂÂÂ color

# Idea of above is that as brightness is for triplet:
#ÂÂ OUT(LED*3 + 0), OUT(LED*3 + 1), OUT(LED*3 + 2),
# Then if we model it like RGB LED then brightness would automatically
# map to correct OUTputs and be grouped from user space point of view
# logically in correct place.

# set first led to red
echo "255 0 0" > /sys/class/leds/lp-led0/color

# set second led to green
echo "0 255 0" > /sys/class/leds/lp-led1/color

# set bank led to blue
echo "0 0 255" > /sys/class/leds/lp-bank-led/color

# Set hardware brightness control to middle
echo "128" > /sys/class/leds/lp-bank-led/brightness

# If we would have software controlled virtual brightness enabled for
# particular led classdev then there would be some math in either user
# or in kernel space.

Thanks,
Vesa JÃÃskelÃinen


--
Best regards,
Jacek Anaszewski