Re: [PATCH v2 1/3] leds: turris-omnia: change max brightness from 255 to 1

[Lee Jones <lee@kernel.org>]

On Sun, 16 Jul 2023, Marek Behún wrote:

> On Sun, 16 Jul 2023 11:19:30 +0200
> Pavel Machek <pavel@ucw.cz> wrote:
> 
> > Hi!
> > 
> > > Using binary brightness makes more sense for this controller, because
> > > internally in the MCU it works that way: the LED has a color, and a
> > > state whether it is ON or OFF.  
> > 
> > So, controller can do (1, 3, 5) but not (3, 3, 3)?
> > 
> > > The resulting brightness computation with led_mc_calc_color_components()
> > > will now always result in either (0, 0, 0) or the multi_intensity value.  
> > 
> > Won't that limit you to 8 colors total?
> > 
> > I guess I`m confused how this hw works...
> 
> Hi Pavel.
> 
> No no no. That's not how it is.
> 
> The HW exposes color control for three channels (RGB), each channel with
> range 0-255 (so 16M colors). The driver exposes this via the
> multi_intensity sysfs file. This is communicated to the HW via
> LED_SET_COLOR I2C command.
> 
> HW also exposes setting the LED ON and OFF, via the LED_SET_STATE
> I2C command.
> 
> We currently have the following sysfs files via which we set LED state
> and color:
>   brightness
>   multi_intensity
> 
> Because currently the driver sets max_brightness to 255, the actual
> color that is sent to HW is recalculated via
> led_mc_calc_color_components(). For example with
> 
>   $ echo 255 255 100 >multi_intensity
>   $ echo 150 >brightness
> 
> the led_mc_calc_color_components() function recalculates the channel
> intensities with formula
>   brightness * channel_intensity / max_brightness
> and so the (255, 255, 100) tuple is converted to (150, 150, 58) before
> sending to HW.
> 
> What I think would make more sense is to make the two sysfs files
>   brightness
>   multi_intensity
> correspond 1-to-1 with I2C commands LED_SET_STATE and LED_SET_COLOR.
> 
> This can be simply done by setting max_brightness to 1. The brightness
> sysfs file then can simply control whether the LED is ON or OFF. The
> multi_intensity file control the color.
> 
> I realize now that in the patch I should also make away with the call
> to led_mc_calc_color_components()...

FYI, due to the revelations above, I'm dropping this from my queue.

-- 
Lee Jones [李琼斯]