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Date:   Fri, 11 Jan 2019 22:52:19 +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

Dan,

On 1/11/19 1:38 PM, Dan Murphy wrote:
> Jacek
> 
> Sorry I missed some replies
> 
> On 1/10/19 4:03 PM, Jacek Anaszewski wrote:
>> 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.
>>
> 
> When the LEDs are banked the banked LEDs are controlled by the bank registers not the LEDx registers
> so you should only see 3 color adjustments on the banked LEDs.
> 
>>>>> 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?
> 
> No.  Independent LED modules are enabled by default.  You have to explicitly enable the banks.
> 
>>
>> 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?
> 
> No it is the opposite.  When the bit is enabled LED banking is enabled and the BANK brightness and color registers over
> ride the LEDx color and brightness registers.
> 
> Default is independent control of the RGB via the LEDx color and brightness registers.
> 
>>
>>> 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.
>>
> 
> Hmm.  I guess I will put that on hold until you read the responses.  I am not sure that would work or
> that would be really clean.  I still believe that mapping led-sources to the LEDx module number is the cleanest
> simplest solution since the driver cannot inter mix different outputs for enablement.

I've read the doc again more carefully and hopefully I finally have
proper understanding. Let's check it.

1. On reset LED_CONFIG0 bits are zeroed, which means
    LEDn module independent control mode.
2. LEDn modules (i.e. IOUT triplets) are controlled independently,
    with use of LEDn_BRIGHTNESS registers, and each IOUT color can
    be adjusted using OUTn_CONTROL registers.
3. LEDn_Bank_EN bits, when set to 1, assign given RGB LED module
    to one global bank, controlled via BANK_BRIGHTNESS and BANK_n_COLOR
    registers.

Having that, I'd see led-sources definitions as follows
(led-sources element is IOUT identifier)

1.

- LED0, LED1, LED2, LED3 modules controlled by separate
   LED class devices

led-sources = <0 1 2>   // LED0
led-sources = <3 4 5>   // LED1
led-sources = <6 7 8>   // LED2
led-sources = <9 10 11> // LED3

2.

- LED0 and LED3 modules assigned to the bank, and controlled
   by one LED class device,
- LED1 and LED2 modules controlled by separate LED class devices

led-sources = <0 1 2 9 10 11> // Bank with LED0 and LED3
led-sources = <3 4 5>         // LED1
led-sources = <6 7 8>         // LED2


So now I see your point. It would be indeed easier
to switch to LEDn module identifiers for led-sources
elements. With that the definitions would look like
this:


1.

- LED0, LED1, LED2, LED3 modules controlled by separate
   LED class devices

led-sources = <0>   // LED0
led-sources = <1>   // LED1
led-sources = <2>   // LED2
led-sources = <3>   // LED3

2.

- LED0 and LED3 modules assigned to the bank, and controlled
   by one LED class device,
- LED1 and LED2 modules controlled by separate LED class devices

led-sources = <0 3> // Bank with LED0 and LED3
led-sources = <1>   // LED1
led-sources = <2>   // LED2


But, I don't think use of led-sources is justified in
this case. I propose to introduce device specific properties:

ti,led-module and ti,led-bank

With that we would have:

ti,led-bank = <0 3>   // Bank with LED0 and LED3 modules
ti,led-module = <1>   // LED1
ti.led-module = <2>   // LED2


>> I would also add Table 1 contents (Bank Number and LED Number
>> Assignment) to the DT bindings.
>>
> 
> Should I add that to the DT binding or reference the data sheet table since this driver will support 4 different devices
> with varying number of outputs from 18-36.

My first thought was to show full table, but four different
mappings would add too much noise. So the reference to the data
sheet should suffice.

-- 
Best regards,
Jacek Anaszewski

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