From mboxrd@z Thu Jan  1 00:00:00 1970
From: Uwe =?iso-8859-1?Q?Kleine-K=F6nig?=  <u.kleine-koenig@pengutronix.de>
Date: Fri, 16 Aug 2019 16:51:48 +0000
Subject: Re: [PATCH v3 2/4] backlight: Expose brightness curve type through sysfs
Message-Id: <20190816165148.7keg45fmlndr22fl@pengutronix.de>
List-Id: <linux-fbdev.vger.kernel.org>
References: <20190709190007.91260-1-mka@chromium.org>
 <20190709190007.91260-3-mka@chromium.org>
In-Reply-To: <20190709190007.91260-3-mka@chromium.org>
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To: Matthias Kaehlcke <mka@chromium.org>
Cc: Thierry Reding <thierry.reding@gmail.com>, Lee Jones <lee.jones@linaro.org>, Daniel Thompson <daniel.thompson@linaro.org>, Jingoo Han <jingoohan1@gmail.com>, Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>, linux-pwm@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-fbdev@vger.kernel.org, linux-kernel@vger.kernel.org, Enric Balletbo i Serra <enric.balletbo@collabora.com>, Douglas Anderson <dianders@chromium.org>, Brian Norris <briannorris@chromium.org>, Pavel Machek <pavel@ucw.cz>, Jacek Anaszewski <jacek.anaszewski@gmail.com>

On Tue, Jul 09, 2019 at 12:00:05PM -0700, Matthias Kaehlcke wrote:
> Backlight brightness curves can have different shapes. The two main
> types are linear and non-linear curves. The human eye doesn't
> perceive linearly increasing/decreasing brightness as linear (see
> also 88ba95bedb79 "backlight: pwm_bl: Compute brightness of LED
> linearly to human eye"), hence many backlights use non-linear (often
> logarithmic) brightness curves. The type of curve currently is opaque
> to userspace, so userspace often uses more or less reliable heuristics
> (like the number of brightness levels) to decide whether to treat a
> backlight device as linear or non-linear.
>=20
> Export the type of the brightness curve via the new sysfs attribute
> 'scale'. The value of the attribute can be 'linear', 'non-linear' or
> 'unknown'. For devices that don't provide information about the scale
> of their brightness curve the value of the 'scale' attribute is 'unknown'.
>=20
> Signed-off-by: Matthias Kaehlcke <mka@chromium.org>

I wonder what kind of problem you are solving here. Can you describe
that in a few words?

Best regards
Uwe

--=20
Pengutronix e.K.                           | Uwe Kleine-K=F6nig            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |