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Subject: Re: [PATCH 1/2] dt: bindings: lp5024: Introduce the lp5024 and lp5018
 RGB driver
To:     Dan Murphy <dmurphy@ti.com>, robh+dt@kernel.org, pavel@ucw.cz
Cc:     devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-leds@vger.kernel.org
References: <20181219162626.12297-1-dmurphy@ti.com>
 <20181219162626.12297-2-dmurphy@ti.com>
 <dc2283f9-db85-1eaf-f046-3fbbd4adcace@gmail.com>
 <2d2d5dcd-9c23-e901-daac-9b79aa5a5e82@ti.com>
 <6c62956e-7789-58ba-5437-f2e033f2825c@gmail.com>
 <366cbf6d-94fa-fea9-be58-07ddb09cff3a@ti.com>
 <df59c10d-7038-cb4a-45f0-7420254c6398@gmail.com>
 <ec0393b7-118e-1f3b-d5af-86ecdf66412a@ti.com>
From:   Jacek Anaszewski <jacek.anaszewski@gmail.com>
Message-ID: <ae700129-7b59-c92b-0c0a-b57a6f230ff7@gmail.com>
Date:   Wed, 9 Jan 2019 22:28:18 +0100
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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@ti.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.

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."
> 

-- 
Best regards,
Jacek Anaszewski