linux-kernel - Re: [PATCH v2 4/4] backlight: pwm_bl: Set scale type for brightness curves specified in the DT

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Message-ID: <20190628081806.GA31375@amd>
Date:   Fri, 28 Jun 2019 10:18:06 +0200
From:   Pavel Machek <pavel@....cz>
To:     Daniel Thompson <daniel.thompson@...aro.org>
Cc:     Matthias Kaehlcke <mka@...omium.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Lee Jones <lee.jones@...aro.org>,
        Jingoo Han <jingoohan1@...il.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        linux-pwm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-fbdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        Douglas Anderson <dianders@...omium.org>,
        Brian Norris <briannorris@...omium.org>,
        Jacek Anaszewski <jacek.anaszewski@...il.com>
Subject: Re: [PATCH v2 4/4] backlight: pwm_bl: Set scale type for brightness
 curves specified in the DT

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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