linux-kernel - Re: [PATCH] backlight: pm8941-wled: Add default-brightness property

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Date:	Wed, 29 Jul 2015 16:51:39 -0700
From:	Bjorn Andersson <bjorn.andersson@...ymobile.com>
To:	Rob Herring <robherring2@...il.com>
CC:	Rob Herring <robh+dt@...nel.org>, Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Jingoo Han <jingoohan1@...il.com>,
	Lee Jones <lee.jones@...aro.org>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	Tomi Valkeinen <tomi.valkeinen@...com>,
	Rob Clark <robdclark@...il.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-fbdev@...r.kernel.org" <linux-fbdev@...r.kernel.org>,
	linux-arm-msm <linux-arm-msm@...r.kernel.org>
Subject: Re: [PATCH] backlight: pm8941-wled: Add default-brightness property

On Fri 24 Jul 08:29 PDT 2015, Rob Herring wrote:

> On Thu, Jul 23, 2015 at 2:52 PM, Bjorn Andersson
> <bjorn.andersson@...ymobile.com> wrote:
> > Add the possibility of specifying the default brightness in DT.
> >
> > Signed-off-by: Bjorn Andersson <bjorn.andersson@...ymobile.com>
> > ---
> >
> > This depends on the patch moving pm8941-wled to backlight [1]. The dt property
> > is used by several other backlight drivers, so I considered this to be a
> > "common" property and it's hence not prefixed with "qcom,".
> 
> Well, we have "default-brightness" and "default-brightness-level" used
> by 1 driver each. But default-brightness-level is much more commonly
> used (in dts files) since it is in the pwm backlight binding, so we
> should go with it. I'd like to see this moved to a common backlight
> doc.
> 

As I looked at these, the default-brightness used in tps65217 is a value
between 0 and 100, so that can be interpreted as a percentage.

The pwm binding however uses a separate array of "brightness-levels" and
then default-brightness-level is supposed to be an index into that
array.


As we're trying to specify a default brightness within the range [0,
max_brightness) the latter doesn't make much sense.

Therefor my suggestion is that we make the "default-brightness" the
common property and we define it as a percentage of [0,max_brightness).

> Really, I think all the backlight documentation should be merged with
> LEDs docs. Things like "default-on" are common. But I won't ask to do
> that here.

I think the backlight framework should be merged with the LED framework.
There's several hw blocks that are split between the two, with an mfd
tying them together...

Regards,
Bjorn
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