Date:   Thu, 10 Jan 2019 23:03:26 +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

On 1/10/19 9:43 PM, Dan Murphy wrote:
> 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@...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.

There is naming conflict I noticed just now - LEDn_BANK_EN bits
in LED_CONFIG0 register enable RGB LED modules, and not BANKs (A,B,C).

> These OUTPUTs will appear as a single RGB LED grouping.

Single? W would rather expect that we get two RGB LED modules, whose
brightness will be controlled via LED0_BRIGHTNESS and LED1_BRIGHTNESS
registers respectively.

>>> 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.

Here as above, I would expect two separate banks - LED0 and LED1.
Moreover - not 3 color adjustment registers, but six - one per iout:
OUT0_COLOR to OUT5_COLOR.

>>> 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.

We have RGB LED modules (enabled with LEDn_Bank_EN bits) and three
banks (A,B,C), which are enabled by default, am I right?

Bank A iouts: 0, 3 ,6, 9, 12, 15
Bank B iouts: 1, 4, 7, 10, 13, 16
Bank C iouts: 2, 5, 8, 11, 14, 17

When RGB LED module is enabled (via LEDn_Bank_EN bit),
the BANK_{A.B,C}_COLOR and BANK_BRIGHTNESS registers
lose control over related IOUTs in favour of LEDn_BRIGHTNESS and
related OUTn_COLOR registers. Is it correct?

> 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.

Ekhm, I messed something here.

So for this I would define a single LED class device.
Related DT node would not need led-sources at all,
but only ti,control-bank. The semantics would be:
controls all iouts not taken by RGB LED modules.

I would also add Table 1 contents (Bank Number and LED Number
Assignment) to the DT bindings.

> 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
> 

-- 
Best regards,
Jacek Anaszewski

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