Date:   Thu, 10 Jan 2019 20:23:02 +0100
From:   Jacek Anaszewski <jacek.anaszewski@...il.com>
To:     Dan Murphy <dmurphy@...com>, Pavel Machek <pavel@....cz>
Cc:     Vesa Jääskeläinen <dachaac@...il.com>,
        robh+dt@...nel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-leds@...r.kernel.org
Subject: Re: Generic RGB LED support was Re: [PATCH 2/2] leds: lp5024: Add the
 LP5024/18 RGB LED driver

Dan,

On 1/10/19 1:46 PM, Dan Murphy wrote:
> 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

Thank you for the videos - they are helpful, and they confirm my first
impression regarding the LEDn_BRIGHTNESS effect. In is shown in the
second video starting from 3:37.

This is the same what I was asking about previously (video [0] from
previous message starting from 1:22). For me this looks similarly
to increasing V of HSV or L of HSL [1].

You denied, so either we interpret colors differently, or there was
some misunderstanding.

[1] http://hslpicker.com

-- 
Best regards,
Jacek Anaszewski

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