Date:   Wed, 9 Jan 2019 15:31:10 -0600
From:   Dan Murphy <dmurphy@...com>
To:     Jacek Anaszewski <jacek.anaszewski@...il.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

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.

Dan

> common LED bindings say:
> 
> - led-sources : List of device current outputs the LED is connected to. The
>                 outputs are identified by the numbers that must be defined
>                 in the LED device binding documentation.
> 
>>> We could additionally mark banks with ti,control-bank,
>>
>> We would have to keep the ti,control-bank node based on the above.
>>
>>> 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?
>>>
>>
>> No it does not.  LED_CONFIG0 sets the bit if it is control bank or not.
> 
> OK, so validation will also have to check if led-sources definitions
> are not mutually exclusive between child DT nodes. For consistency it
> would be really better if bank definitions also used led-sources.
> 
>> Section 8.3.2 in the data sheet says
>> "When a channel is configured in
>> LED bank-control mode, the related color mixing and intensity control is governed by the bank control registers
>> (BANK_A_COLOR, BANK_B_COLOR, BANK_C_COLOR, and BANK_BRIGHTNESS) regardless of the inputs
>> on its own color-mixing and intensity-control registers."
>>
> 


-- 
------------------
Dan Murphy

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