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Subject: Re: [PATCH 1/2] dt: bindings: lp5024: Introduce the lp5024 and lp5018
 RGB driver
To:     Jacek Anaszewski <jacek.anaszewski@gmail.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>
 <ae700129-7b59-c92b-0c0a-b57a6f230ff7@gmail.com>
 <adcd7987-f7fc-ae1f-9aa4-cebcbf01ad58@ti.com>
 <1702dfd6-b08f-c1ff-e46d-1366618bedb0@gmail.com>
 <72112839-11d4-54be-df94-b2322f77cb0f@ti.com>
 <8b126077-c200-ed34-03b7-6d43a22fb0c9@gmail.com>
From:   Dan Murphy <dmurphy@ti.com>
Message-ID: <92cc81dc-7280-8bf0-9536-9c4d990eaf3b@ti.com>
Date:   Thu, 10 Jan 2019 14:43:54 -0600
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Jacek

On 1/10/19 1:57 PM, Jacek Anaszewski wrote:
> 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@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.
>>>>>
>>>>
>>>> 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.
> 

I am as well but as I tried to explain that if you define OUT0 as bank controlled then OUT1 and OUT2 are also bank controlled
within the hardware.  We have no control of that.  If BIT(0) and BIT(1) are set in the LED_CONFIG0 register then OUT0, 1, 2, 3, 4 and 5 are all bank controlled.

These OUTPUTs will appear as a single RGB LED grouping.

>> 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.

Yes but there is no BANK output pin just like there is no dedicated LEDn output pin.  The banks are grouped internally to the device
so again if OUT0 and OUT3 are defined as banked then 1, 2, 4, and 5 are all mapped to the bank.  1 BANK brightness register and 3 bank
color adjustment registers.

> 
>> 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.
> 

Yes.  When the RGBs are banked you have to think of them as a single RGB LED cluster and not as separate RGB LED clusters.
As you know the brightness is controlled by the single BANK_BRIGHTNESS register.  So identifying each output in the led-sources is
misleading as the hardware does this all on the chip.  This is why I just mapped each output to the Virtual LEDx module.

If you define LED0 and LED1 as banked then OUT0->5 are banked and it would be considered a single virtual output.

LED_CONFIG0 even uses the modular approach to define what is banked and what is not.  With the modular approach to led-sources
the mapping of the sources to the CONFIG register become 1-1.

1 = LED7 bank control mode enabled
0 = LED7 independent control mode enabled

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