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Subject: Re: Generic RGB LED support was Re: [PATCH 2/2] leds: lp5024: Add the
 LP5024/18 RGB LED driver
From:   Dan Murphy <dmurphy@ti.com>
To:     Jacek Anaszewski <jacek.anaszewski@gmail.com>,
        Pavel Machek <pavel@ucw.cz>
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        <linux-kernel@vger.kernel.org>, <linux-leds@vger.kernel.org>
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Date:   Thu, 10 Jan 2019 06:46:26 -0600
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Jacek

On 1/8/19 3:25 PM, Dan Murphy wrote:
> Jacek
> 
> On 1/8/19 3:18 PM, Jacek Anaszewski wrote:
>> Hi Dan,
>>
>> On 1/7/19 10:14 PM, Dan Murphy wrote:
>>> Jacek
>>>
>>> On 1/7/19 2:59 PM, Jacek Anaszewski wrote:
>>>> Dan,
>>>>
>>>> On 1/7/19 8:36 PM, Dan Murphy wrote:
>>>>> Jacek
>>>>>
>>>>> On 1/7/19 1:13 PM, Jacek Anaszewski wrote:
>>>>>> On 1/6/19 4:52 PM, Jacek Anaszewski wrote:
>>>>>>> Hi Pavel,
>>>>>>>
>>>>>>> On 1/5/19 11:12 PM, Pavel Machek wrote:
>>>>>>>> Hi!
>>>>>>>>
>>>>>>>>>> Grab yourself an RGB LED and play with it; you'll see what the
>>>>>>>>>> problems are. It is hard to explain colors over email...
>>>>>>>>>
>>>>>>>>> Video [0] gives some overview of lp5024 capabilities.
>>>>>>>>>
>>>>>>>>> I don't see any problems in exposing separate red,green,blue
>>>>>>>>> files and brightness for the devices with hardware support for
>>>>>>>>> that.
>>>>>>>>
>>>>>>>> Well, that's what we do today, as three separate LEDs, right?
>>>>>>>
>>>>>>> No. It doesn't allow for setting color intensity by having
>>>>>>> the color fixed beforehand. Below is relevant excerpt from
>>>>>>> the lp5024 documentation. This is not something that can be
>>>>>>> mapped to RGB color space, but rather to HSV/HSL, with the
>>>>>>> reservation that the hardware implementation uses PWM
>>>>>>> for setting color intensity.
>>>>>>>
>>>>>>> <quote>
>>>>>>> 8.3.1.2 Independent Intensity Control Per RGB LED Module
>>>>>>>
>>>>>>> When color is fixed, the independent intensity-control is used to
>>>>>>> achieve accurate and flexible dimming control for every RGB LED module.
>>>>>>>
>>>>>>> 8.3.1.2.1 Intensity-Control Register Configuration
>>>>>>>
>>>>>>> Every three consecutive output channels are assigned to their respective
>>>>>>> intensity-control register (LEDx_BRIGHTNESS). For example, OUT0, OUT1,
>>>>>>> and OUT2 are assigned to LED0_BRIGHTNESS, so it is recommended to
>>>>>>> connect the RGB LEDs in the sequence as shown in Table 1. The LP50xx
>>>>>>> device allows 256-step intensity control for each RGB LED module, which
>>>>>>> helps achieve a smooth dimming effect.
>>>>>>> </quote>
>>>>>>>
>>>>>>>> I don't have problem with that, either; other drivers already do
>>>>>>>> that. He's free to use existing same interface.
>>>>>>>>
>>>>>>>> But that is insufficient, as it does not allow simple stuff, such as
>>>>>>>> turning led "white".
>>>>>>>>
>>>>>>>> So... perhaps we should agree on requirements, first, and then we can
>>>>>>>> discuss solutions?
>>>>>>>>
>>>>>>>> Requirements for RGB LED interface:
>>>>>>>>
>>>>>>>> 1) Userspace should be able to set the white color
>>>>>>>>
>>>>>>>> 2) Userspace should be able to arbitrary color from well known list
>>>>>>>> and it should approximately match what would CRT, LCD or OLED monitor display
>>>>>>>
>>>>>>> The difference is that monitor display driver is pre-calibrated
>>>>>>> for given display by the manufacturer. With the LED controllers the
>>>>>>> manufacturer has no control over what LEDs will be connected to the
>>>>>>> iouts. Therefore it should be not surprising that colors produced
>>>>>>> by custom LEDs are not as user would expect when comparing to
>>>>>>> the RGB color displayed on the monitor display.
>>>>>>>
>>>>>>> TI provides "Various LED Ring Lighting Patterns Reference Design" [0]
>>>>>>> that show how to produce various patterns with use of the reference
>>>>>>> board with LED ring built using sixteen 19-337/R6GHBHC-A01/2T LEDs [1].
>>>>>>>
>>>>>>> Document [0] mentions also specific "Design considerations" in the
>>>>>>> chapter 2.2:
>>>>>>>
>>>>>>> <quote>
>>>>>>> Several considerations are taken into account for this particular design:
>>>>>>> ? LED map (ring) for meeting the requirement of popular human-machine interaction style.
>>>>>>> ? LED size, numbers and the diffuse design for meeting lighting pattern uniformity.
>>>>>>> ? Analog dimming in the difference ambient light lux without losing dimming resolution in lighting pattern.
>>>>>>>
>>>>>>> These considerations apply to most human-machine interaction end equipment with day and night vision
>>>>>>> designs in some way, but the designer must decide the particular considerations to take into account for a
>>>>>>> specific design.
>>>>>>> </quote>
>>>>>>>
>>>>>>> This renders your requirement 2) infeasible with use of custom LEDs
>>>>>>> any fixed algorithm, since the final effect will always heavily depend
>>>>>>
>>>>>> Typo here: s/any fixed/and fixed/
>>>>>>
>>>>>>> on the LED circuit design.
>>>>>>>
>>>>>>>>
>>>>>>>> ?????? 2a) LEDs probably slightly change color as they age. That's out of
>>>>>>>> ?????? scope, unless the variation is much greater than on monitors.
>>>>>>>>
>>>>>>>> ?????? 2b) Manufacturing differences cause small color variation. Again,
>>>>>>>> ?????? that's out of scope, unless the variation is much greater than on
>>>>>>>> ?????? monitors.
>>>>>>>>
>>>>>>>> Nice to have features:
>>>>>>>>
>>>>>>>> 3) Full range of available colors/intensities should be available to
>>>>>>>> userspace
>>>>>>>>
>>>>>>>> 4) Interface should work well with existing triggers
>>>>>>>>
>>>>>>>> 5) It would be nice if userland knew how many lumens are produced at
>>>>>>>> each wavelength for each setting (again, minus aging and manufacturing
>>>>>>>> variations).
>>>>>>>>
>>>>>>>> 6) Complexity of math in kernel should be low, and preferably it
>>>>>>>> should be integer or fixed point
>>>>>>>>
>>>>>>>> Problems:
>>>>>>>>
>>>>>>>> a) RGB LEDs are usually not balanced. Setting 100% PWM on
>>>>>>>> red/green/blue channels will result in nothing close to white
>>>>>>>> light. In fact, to get white light on N900, blue and green channel's
>>>>>>>> PWM needs to be set pretty low, as in 5%.
>>>>>>>>
>>>>>>>> b) LED class does not define any relation between "brightness" in
>>>>>>>> sysfs and ammount of light in lumens. Some drivers use close to linear
>>>>>>>> relation, some use exponential relation. Human eyes percieve logarithm
>>>>>>>> of lumens. RGB color model uses even more complex function.
>>>>>>>>
>>>>>>>> c) Except for white LEDs, LEDs are basically sources of single
>>>>>>>> wavelength of light, while CRTs and LCDs produce broader
>>>>>>>> spectrums.
>>>>>>>>
>>>>>>>> d) RG, RGBW and probably other LED combinations exist.
>>>>>>>>
>>>>>>>> e) Not all "red" LEDs will produce same wavelength. Similar
>>>>>>>> differences will exist for other colors.
>>>>>>>>
>>>>>>>> f) We have existing RGB LEDs represented as three separate
>>>>>>>> monochromatic LEDs in sysfs.
>>>>>>>
>>>>>>> One general question: do you have any solutions in store?
>>>>>>>
>>>>>>> [0] http://www.ti.com/lit/ug/tiduee6/tiduee6.pdf
>>>>>>> [1] http://www.everlight.com/file/ProductFile/19-337-R6GHBHC-A01-2T.pdf
>>>>>>>
>>>>>>
>>>>>
>>>>> I just wanted to point out that there are 4 total devices right now that use the same mapping
>>>>>
>>>>> LP5018, LP5024, LP5030 and the LP5036.
>>>>>
>>>>> I can implement what ever we would like to I just need to know what to design against.
>>>>
>>>> As you can see from the discussion in this thread it may take some
>>>> time to work out the interface satisfying everyone. I made some design
>>>> proposal, but Pavel had no warm word for it. It would be easier if
>>>> we had more opinions.
>>>
>>> I got it from the threads and just the time invested in the FW and HSV.
>>>
>>>>
>>>> How do you feel about using brightness file for setting LEDn_BRIGHTNESS?
>>>
>>> I am using that now.? The brightness file will adjust the overall brightness of the LED group
>>> or bank pending on how the LEDs are grouped in the DT file.
>>>
>>>>
>>>> Does increasing LEDn_BRIGHTNESS value (i.e. color intensity) feel like
>>>> increasing color lightness (i.e. the pattern presented in the video [0]
>>>> starting from 1:22)?
>>>
>>> No unfortunately this is why I introduced the new files to control the individual RGB intensities
>>> so that the designers can set, tune, create color variations or patterns like the video.
>>>
>>> The RGB group brightness would be independent based on lighting conditions, enclosures and diffusers.
>>> So you could technically be changing color and overall brightness virtually simultaneously
>>
>> Oh, so this is surprising. Now it gets even more obscure to me.
>>
>> It would be really helpful if we could see a video showing
>> the LED effects with regard to the applied settings.
> 
> Well I am doing a test off the command line to ensure the user space can interface with the RGB LED.
> 
> I can ping someone in product development to see the application of this device if that would help.
> We did give them a test driver to work on their features but told them the driver is not final until it
> is in the mainline kernel
> 
> Dan
> 
>>
>>>>> But keep in mind I still need to invest my time in the other TI-lmu patches on my list to complete.
>>>>
>>>> Do what you deem most suitable for you. We are here only to help
>>>> merging the patches, but keeping in mind that kernel interface once
>>>> introduced must be preserved forever. Therefore we need to do our
>>>> best to make the best possible design decisions.
>>>>
>>>> [0] https://www.youtube.com/watch?v=qdt-alh8i6E
>>>>
>>>
>>> I understand.? Maybe I can make the files generic to use for either control or individual control.
>>>
>>> We can probably define new ABI's until either HSV or DT frameworks get going.? And them make the file presentation
>>> configurable and default to the new files.
>>
>> I am leaning towards it. Just commented on your patches.
>>
> 
> 

Asked the HW team for videos this is what they sent
https://training.ti.com/lp50x-led-drivers-achieve-optimal-color-brightness-zero-audible-noise
https://training.ti.com/how-configuring-led-brightness-color-and-patterns-lp50x-gui-tool

Not sure how helpful these would be

Dan

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