Date:   Thu, 10 Jan 2019 20:57:50 +0100
From:   Jacek Anaszewski <jacek.anaszewski@...il.com>
To:     Dan Murphy <dmurphy@...com>, robh+dt@...nel.org, pavel@....cz
Cc:     devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-leds@...r.kernel.org
Subject: Re: [PATCH 1/2] dt: bindings: lp5024: Introduce the lp5024 and lp5018
 RGB driver

Dan,

On 1/10/19 8:22 PM, Dan Murphy wrote:
> Jacek
> 
> On 1/10/19 12:44 PM, Jacek Anaszewski wrote:
>> Hi Dan,
>>
>> On 1/9/19 10:31 PM, Dan Murphy wrote:
>>> Jacek
>>>
>>> On 1/9/19 3:28 PM, Jacek Anaszewski wrote:
>>>> On 1/9/19 10:12 PM, Dan Murphy wrote:
>>>>> On 1/9/19 2:12 PM, Jacek Anaszewski wrote:
>>>>>> Hi Dan,
>>>>>>
>>>>>> On 1/8/19 10:22 PM, Dan Murphy wrote:
>>>>>>> On 1/8/19 3:16 PM, Jacek Anaszewski wrote:
>>>>>>>> On 1/8/19 9:53 PM, Dan Murphy wrote:
>>>>>>>>> Jacek
>>>>>>>>>
>>>>>>>>> On 1/8/19 2:33 PM, Jacek Anaszewski wrote:
>>>>>>>>>> Dan,
>>>>>>>>>>
>>>>>>>>>> On 12/19/18 5:26 PM, Dan Murphy wrote:
>>>>>>>>>>> Introduce the bindings for the Texas Instruments LP5024 and the LP5018
>>>>>>>>>>> RGB LED device driver.  The LP5024/18 can control RGB LEDs individually
>>>>>>>>>>> or as part of a control bank group.  These devices have the ability
>>>>>>>>>>> to adjust the mixing control for the RGB LEDs to obtain different colors
>>>>>>>>>>> independent of the overall brightness of the LED grouping.
>>>>>>>>>>>
>>>>>>>>>>> Datasheet:
>>>>>>>>>>> http://www.ti.com/lit/ds/symlink/lp5024.pdf
>>>>>>>>>>>
>>>>>>>>>>> Signed-off-by: Dan Murphy <dmurphy@...com>
>>>>>>>>>>> ---
>>>>>>>>>>>        .../devicetree/bindings/leds/leds-lp5024.txt  | 63 +++++++++++++++++++
>>>>>>>>>>>        1 file changed, 63 insertions(+)
>>>>>>>>>>>        create mode 100644 Documentation/devicetree/bindings/leds/leds-lp5024.txt
>>>>>>>>>>>
>>>>>>>>>>> diff --git a/Documentation/devicetree/bindings/leds/leds-lp5024.txt b/Documentation/devicetree/bindings/leds/leds-lp5024.txt
>>>>>>>>>>> new file mode 100644
>>>>>>>>>>> index 000000000000..9567aa6f7813
>>>>>>>>>>> --- /dev/null
>>>>>>>>>>> +++ b/Documentation/devicetree/bindings/leds/leds-lp5024.txt
>>>>>>>>>>> @@ -0,0 +1,63 @@
>>>>>>>>>>> +* Texas Instruments - LP5024/18 RGB LED driver
>>>>>>>>>>> +
>>>>>>>>>>> +The LM3692x is an ultra-compact, highly efficient,
>>>>>>>>>>> +white-LED driver designed for LCD display backlighting.
>>>>>>>>>>> +
>>>>>>>>>>> +The main difference between the LP5024 and L5018 is the number of
>>>>>>>>>>> +RGB LEDs they support.  The LP5024 supports twenty four strings while the
>>>>>>>>>>> +LP5018 supports eighteen strings.
>>>>>>>>>>> +
>>>>>>>>>>> +Required properties:
>>>>>>>>>>> +    - compatible:
>>>>>>>>>>> +        "ti,lp5018"
>>>>>>>>>>> +        "ti,lp5024"
>>>>>>>>>>> +    - reg :  I2C slave address
>>>>>>>>>>> +    - #address-cells : 1
>>>>>>>>>>> +    - #size-cells : 0
>>>>>>>>>>> +
>>>>>>>>>>> +Optional properties:
>>>>>>>>>>> +    - enable-gpios : gpio pin to enable/disable the device.
>>>>>>>>>>> +    - vled-supply : LED supply
>>>>>>>>>>> +
>>>>>>>>>>> +Required child properties:
>>>>>>>>>>> +    - reg : Is the child node iteration.
>>>>>>>>>>> +    - led-sources : LP5024 - 0 - 7
>>>>>>>>>>> +            LP5018 - 0 - 5
>>>>>>>>>>> +            Declares the LED string or strings that the child node
>>>>>>>>>>> +            will control.  If ti,control-bank is set then this
>>>>>>>>>>> +            property will contain multiple LED IDs.
>>>>>>>>>>> +
>>>>>>>>>>> +Optional child properties:
>>>>>>>>>>> +    - label : see Documentation/devicetree/bindings/leds/common.txt
>>>>>>>>>>> +    - linux,default-trigger :
>>>>>>>>>>> +       see Documentation/devicetree/bindings/leds/common.txt
>>>>>>>>>>> +    - ti,control-bank : Indicates that the LED strings declared in the
>>>>>>>>>>> +                led-sources property are grouped within a control
>>>>>>>>>>> +                bank for brightness and mixing control.
>>>>>>>>>>> +
>>>>>>>>>>> +Example:
>>>>>>>>>>> +
>>>>>>>>>>> +led-controller@28 {
>>>>>>>>>>> +    compatible = "ti,lp5024";
>>>>>>>>>>> +    reg = <0x28>;
>>>>>>>>>>> +    #address-cells = <1>;
>>>>>>>>>>> +    #size-cells = <0>;
>>>>>>>>>>> +
>>>>>>>>>>> +    enable-gpios = <&gpio1 28 GPIO_ACTIVE_HIGH>;
>>>>>>>>>>> +    vled-supply = <&vbatt>;
>>>>>>>>>>> +
>>>>>>>>>>> +    led@0 {
>>>>>>>>>>> +        reg = <0>;
>>>>>>>>>>> +        led-sources = <1>;
>>>>>>>>>>> +    };
>>>>>>>>>>> +
>>>>>>>>>>> +    led@1 {
>>>>>>>>>>> +        reg = <1>;
>>>>>>>>>>> +        led-sources = <0 6>;
>>>>>>>>>>> +        ti,control-bank;
>>>>>>>>>>
>>>>>>>>>> Do you really need ti,control-bank? Doesn't led-sources array size
>>>>>>>>>> greater than 1 mean that the node describes control bank?
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>> That will work too.
>>>>>>>>
>>>>>>>>>> Also, does it make sense to have only two LEDs in the bank?
>>>>>>>>>
>>>>>>>>> The array can populate all 7 LEDs in a single node.  I only show 2 here as the example.
>>>>>>>>> See the description above of the led-sources
>>>>>>>>
>>>>>>>> OK, I confused RGB LED modules with banks.
>>>>>>>>
>>>>>>>> Shouldn't we allow for defining either strings or RGB LED
>>>>>>>> triplets somehow then?
>>>>>>>>
>>>>>>>
>>>>>>> Well that is what this should be doing.  If you define a single LED in LED sources then
>>>>>>> the triplet is controlled via the associated LEDx_brightness register.
>>>>>>
>>>>>> led-sources should map to iouts directly.
>>>>>> So, for RGB LED modules I would expect:
>>>>>>
>>>>>> LED0: led-sources = <0 1 2>;
>>>>>> LED1: led-sources = <3 4 5>;
>>>>>> LED2: led-sources = <6 7 8>;
>>>>>> and so on.
>>>>>
>>>>>>
>>>>>> for banks:
>>>>>>
>>>>>> Bank A with iouts 0,3,6,9: led-sources<0 3 6 9>;
>>>>>> Bank B with iouts 2,4,10:  led-sources<2 4 10>;
>>>>>> Bank C with iouts 5,8,11,14,17: led-sources<5 8 11 14 17>;
>>>>>>
>>>>>
>>>>> Ok the led-sources would need to be different then this as I don't define the sources for banks.
>>>>>
>>>>> The led-sources for the banks and the individual groups will have different meanings within the same
>>>>> document.  I was attempting to keep the led-sources mapped to the LEDx_brightness registers as opposed to
>>>>> the hardware outputs since the RGB LEDs are controlled and grouped by a single brightness register and if banked then
>>>>> it would be controlled by the bank brightness register.
>>>>>
>>>>> Describing these in the DT seems wrought with potential issues as the data sheet defines what outputs map to what bank and LED
>>>>> registers.
>>>>
>>>> Yes, that's why I mentioned the need for validation of led-sources.
>>>> But they have to be iouts. This property was introduced specifically
>>>> for such purposes.
>>>>
>>>
>>> Yes Pavel also mentioned that as well.
>>>
>>> I will look into validating the sources.  But there will be no mapping of the sources to the output that is done
>>> in the hardware.  This would just be a data sheet mapping since the outputs are not configurable.
>>
>> Hmm, isn't the mapping defined in the hardware via LED_CONFIG0 register?
>> I have an impression that it defines whether LED belongs to an RGB LED
>> module or to a bank. Basing on that I created my DT example above.
>>
> 
> Yes so if you turn on the bank control for LED0 and LED1 then
> out 0, 3 are mapped to BANK A
> out 1, 4 are mapped to BANK B

Just noticed that I made a mistake in my example, it should have been:

Bank B with iouts 1,4,10:  led-sources<1 4 10>;

> out 2, 5 are mapped to BANK C

Correct.

> All done automatically in the hardware and the LED0_BRIGHTNESS and LED1_BRIGHTNESS registers have no affect on the brightness

That's right.

> If we grouped the LEDs into a bank the led-sources would look more like this
> led-sources = < 0 1 2 3 4 5 >;

Why? This would be a mix of three banks. Like you listed above.
I'm still interpreting led-sources elements as iout identifiers.

> ti,control-bank; // But this can be omitted as led-sources is greater then 3
> 
> non-banked case would be
> led-sources = < 0 1 2 >;

Agreed here. It would be LED0 RGB LED module.
> But the actual OUT numbers don't matter in the bank case unless we do the validation.  There would need to be an algorithim
> that translates these output to the correct LEDx register and CONFIG0 bits.  Basically if OUT0 is mapped to the bank then OUT1 and OUT2
> are inherently mapped to the bank.  

To three separate banks, right?
OUT0 - bank A, OUT1 - bank B, OUT2 - bank C.

> They cannot be separated so the device theoretically treats the RGB group as a single LED.  And
> when banked it treats the groups of RGBs that are defined as a single LED.
> 
> This is why it was easier use the LEDx out as the virtual out as we only need to define the group number(s) that are controled by the
> LED file presented to the user space.

I suspect there is logical clash here due to interpreting
led-sources elements as iouts in one case and LEDn modules
in the other case.

-- 
Best regards,
Jacek Anaszewski

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