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: <20190626145617.GB22348@xo-6d-61-c0.localdomain>
Date:   Wed, 26 Jun 2019 16:56:18 +0200
From:   Pavel Machek <pavel@....cz>
To:     Matthias Kaehlcke <mka@...omium.org>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Lee Jones <lee.jones@...aro.org>,
        Daniel Thompson <daniel.thompson@...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 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.

									Pavel