Re: [PATCH] ARM: dts: imx6qdl: Adjust the brightness setting for LVDS panel

[Philipp Zabel <p.zabel@pengutronix.de>]

Am Dienstag, den 20.01.2015, 19:38 +0800 schrieb Shawn Guo:
> Add LAKML and a few interested people.
> 
> Shawn
> 
> On Tue, Jan 20, 2015 at 06:22:35PM +0800, Robby Cai wrote:
> > Hannstar XGA panel is used by default on i.MX6QDL Sabre Auto/Lite/SD
> > or derived board.
> > 
> > According to its data sheet [1],
> > a) the dimming duty cycle is 20% - 100%.
> > This patch changes the brightness-level from 20 to 100 with step 10 to
> > make it straight-forward.
> > b) the typical dimming frequency is 20KHz.
> > The previous setting is 200Hz. This patch corrects it.
> > 
> > [1]
> > http://boundarydevices.com/wp-content/uploads/2013/06/HSD100PXN1-A00-C11-1.0.pdf
> > 
> > Signed-off-by: Robby Cai <r63905@freescale.com>
> > ---
> >  arch/arm/boot/dts/imx6qdl-gw52xx.dtsi     | 6 +++---
> >  arch/arm/boot/dts/imx6qdl-gw53xx.dtsi     | 6 +++---
> >  arch/arm/boot/dts/imx6qdl-gw54xx.dtsi     | 6 +++---
> >  arch/arm/boot/dts/imx6qdl-nitrogen6x.dtsi | 6 +++---
> >  arch/arm/boot/dts/imx6qdl-sabreauto.dtsi  | 6 +++---
> >  arch/arm/boot/dts/imx6qdl-sabrelite.dtsi  | 6 +++---
> >  arch/arm/boot/dts/imx6qdl-sabresd.dtsi    | 6 +++---
> >  7 files changed, 21 insertions(+), 21 deletions(-)
> > 
> > diff --git a/arch/arm/boot/dts/imx6qdl-gw52xx.dtsi b/arch/arm/boot/dts/imx6qdl-gw52xx.dtsi
> > index b5756c2..33484d8 100644
> > --- a/arch/arm/boot/dts/imx6qdl-gw52xx.dtsi
> > +++ b/arch/arm/boot/dts/imx6qdl-gw52xx.dtsi
> > @@ -29,9 +29,9 @@
> >  
> >  	backlight {
> >  		compatible = "pwm-backlight";
> > -		pwms = <&pwm4 0 5000000>;
> > -		brightness-levels = <0 4 8 16 32 64 128 255>;
> > -		default-brightness-level = <7>;
> > +		pwms = <&pwm4 0 50000>;
> > +		brightness-levels = <0 20 30 40 50 60 70 80 90 100>;
> > +		default-brightness-level = <9>;

I notice that the intervals are changed from exponential to linear.
Is this really wanted here?
I expect that the new settings result in huge steps in perceived
brightness at low levels and a nearly imperceptible change at the
last step.

regards
Philipp