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Date:   Wed, 9 Jan 2019 21:12:15 +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

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>;

We could additionally mark banks with ti,control-bank,
but I'm not sure if it would ease parsing, since
you will have to validate iouts configuration anyway.

> If you have multiple LED sources defined in the led-sources then those LEDs would be grouped in the bank.
> I guess I need to provide some protection or a warning if a DT defines two banks because there is only one bank control.

Does the hardware allow the IOUT to belong to an RGB LED module
and to a bank in the same time?

-- 
Best regards,
Jacek Anaszewski

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