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Subject: Re: Re: [PATCH v3 2/4] backlight: Expose brightness curve type
 through sysfs
To:     Matthias Kaehlcke <mka@chromium.org>,
        Thierry Reding <thierry.reding@gmail.com>,
        Lee Jones <lee.jones@linaro.org>,
        Jingoo Han <jingoohan1@gmail.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Cc:     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>
References: <20190709190007.91260-1-mka@chromium.org>
 <20190709190007.91260-3-mka@chromium.org>
 <20190807201528.GO250418@google.com>
From:   Daniel Thompson <daniel.thompson@linaro.org>
Message-ID: <510f6d8a-71a0-fa6e-33ea-c4a4bfa96607@linaro.org>
Date:   Fri, 16 Aug 2019 16:54:18 +0100
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On 07/08/2019 21:15, Matthias Kaehlcke wrote:
> 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.
>>
>> 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'.
>>
>> Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
> 
> Daniel (et al): do you have any more comments on this patch/series or
> is it ready to land?

I decided to leave it for a long while for others to review since I'm 
still a tiny bit uneasy about the linear/non-linear terminology.

However that's my only concern, its fairly minor and I've dragged by 
feet for more then long enough, so:
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>


Daniel.