linux-kernel - Re: [PATCH] thinkpad_acpi: don't yell on unsupported brightness interfaces

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Date:	Fri, 8 Jan 2016 17:26:28 +0000
From:	Eric Curtin <ericcurtin17@...il.com>
To:	David Herrmann <dh.herrmann@...il.com>
Cc:	Darren Hart <dvhart@...radead.org>,
	Henrique de Moraes Holschuh <hmh@....eng.br>,
	platform-driver-x86@...r.kernel.org,
	ibm-acpi-devel@...ts.sourceforge.net,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] thinkpad_acpi: don't yell on unsupported brightness interfaces

On 8 January 2016 at 11:55, David Herrmann <dh.herrmann@...il.com> wrote:
> Hi
>
> On Thu, Jan 7, 2016 at 2:03 AM, Eric Curtin <ericcurtin17@...il.com> wrote:
>> Also another query, could be a mini-side project for me as I'm a
>> beginner kernel dev when I have some spare time. Could we change the
>> minimum brightness value not to be off? 0 does not have to mean
>> backlight off from reading various things around the web:
>>
>> http://www.x.org/wiki/Events/XDC2014/XDC2014GoedeBacklight/backlight.pdf
>>
>> And to be honest having the ability to completely turn off the
>> backlight is a useless function and is probably unintended as discussed
>> in the github thread above also. You would need night vision googles to
>> read the screen in this state! I'm pretty sure the Windows driver does
>> not completely turn off the screen on minimum brightness either, no
>> need to have different functionality on different platforms especially
>> when this functionality isn't very useful.
>
> Whether '0' means 'off' or 'lowest brightness level' has been
> discussed several times. Sadly, we cannot change semantics without
> breaking user-space, so you better work around it. There have been
> several proposals to fix it, but I guess no-one cared so far.
>
> Anyway, both features (turning backlight off *and* lowest backlight
> level) _are_ used actively by user-space. Hence, both should be
> supported.
>
> Thanks
> David

As regards the "Unsupported brightness interface" log message will I
add 101 to the switch statement so it doesn't get reported on my device
or just remove it? This seems to be reporting many false positives (or
negatives whatever way you want to look at it) on different machines so
can I remove this logging?