linux-kernel - Re: [PATCH v2 3/4] ARM: dts: imx6qdl-colibri: backlight pwm: Simplify inverted backlight

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Date:   Wed, 11 May 2022 10:35:20 -0300
From:   Fabio Estevam <festevam@...il.com>
To:     Max Krummenacher <max.oss.09@...il.com>
Cc:     Max Krummenacher <max.krummenacher@...adex.com>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        NXP Linux Team <linux-imx@....com>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Rob Herring <robh+dt@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Shawn Guo <shawnguo@...nel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 3/4] ARM: dts: imx6qdl-colibri: backlight pwm: Simplify
 inverted backlight

On Wed, May 11, 2022 at 10:32 AM Max Krummenacher <max.oss.09@...il.com> wrote:

> I disagree. Just setting the invert without at the same changing the
> brightness-levels does
> change the user experience way more than when one adapts the available
> duty cycles
> at the same time.
>
> With the change to use the PWM with inverted polarity the PWM signals
> is inverted to
> how it was before this patch. Keeping the brightness-levels will then
> have a big brightness
> jump from 0 to 127 duty cycle, the other 6 steps will then be barely noticable.
>
> I.e. before the change the brightness for level [0..7] was
> ['off', 128/255, 64/255, 32/255, 16/255, 8/255, 4/255, 'off'],
> if one only inverts the polarity it will be
> ['off', 128/255, 191/255, 223/255, 239/255, 247/255, 255/255].
> With the proposed patch it will be
> ['off', 4/255, 8/255, 16/255, 32/255, 64/255, 128/255, 255/255].

Ok, please add an explanation to the commit log as to why you are
changing the brightness levels
like you did here. Thanks