# Re: \[PATCH v2 4/4\] backlight: pwm\_bl: Set scale type for brightness curves specified in the DT

- From: Pavel Machek \<hidden\>
- Date: 2019-06-28 08:18:10 
- List: linux-fbdev
- Page: https://ratatoskr.run/linux-fbdev/2019/06/5643106
- Thread: https://ratatoskr.run/linux-pwm/2019/06/5638592/t.md

```text
On Fri 2019-06-28 08:55:16, Daniel Thompson wrote:
> On Wed, Jun 26, 2019 at 04:56:18PM +0200, Pavel Machek wrote:
> > On Mon 2019-06-24 13:31:13, Matthias Kaehlcke wrote:
> > > Check if a brightness curve specified in the device tree is linear or
> > > not and set the corresponding property accordingly. This makes the
> > > scale type available to userspace via the 'scale' sysfs attribute.
> > > 
> > > To determine if a curve is linear it is compared to a interpolated linear
> > > curve between min and max brightness. The curve is considered linear if
> > > no value deviates more than +/-5% of ${brightness_range} from their
> > > interpolated value.
> > 
> > I don't think this works. Some hardware does takes brightness in perceptual units,
> > converting it in the LED controller.
> 
> This check is exclusive to PWM backlights so I'd like to double check
> that you are thinking specifically of hardware that takes it's signal
> from the PWM and works in perceptual units?

I missed that details. Taking PWM input then converting it to
perceptual units would indeed be strange.

Sorry,
									Pavel

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
```

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