From mboxrd@z Thu Jan  1 00:00:00 1970
From: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Date: Wed, 14 Sep 2016 15:20:38 +0000
Subject: [U-Boot] [PATCH v1 3/5] colibri_t20: fix display configuration
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 <b5e96b82-3f8f-55c2-d3b8-28c1f76a4827@wwwdotorg.org>
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On Mon, 2016-09-12 at 12:18 -0600, Stephen Warren wrote:
> On 09/09/2016 10:10 AM, Marcel Ziswiler wrote:
> > 
> > Without this patch the following error will be shown:
> > 
> > stdio_add_devices: Video device failed (ret=-22)
> > 
> > As commit ec5507707a1d1e84056a6c864338f95f6118d3ca (video: tegra:
> > Move
> > to using simple-panel and pwm-backlight) states the Colibri T20
> > needs
> > updating too which this patch finally attempts doing.
> > 
> > Please note that the current U-Boot implementation requires a dummy
> > GPIO e.g. for a fixed backlight regulator to be explicitly defined
> > in
> > order to work unlike in the Linux kernel where this is taken care
> > of
> > automatically.
> The binding documentation does state that the power supply is
> mandatory.

Yes, of course.

> > diff --git a/arch/arm/dts/tegra20-colibri.dts
> > b/arch/arm/dts/tegra20-colibri.dts
> > 
> > +	regulators {
> > +		compatible = "simple-bus";
> > +		#address-cells = <1>;
> > +		#size-cells = <0>;
> > +
> > +		reg_dummy: regulator at 0 {
> Why call this a dummy? This is a real regulator that describes the
> power?
> supply to the backlight. Even if there's no SW control over the power
> to?
> the backlight, there is still a (fixed) power source, and this DT
> node?
> represents that power source.

OK.

> > +			compatible = "regulator-fixed";
> > +			reg = <0>;
> > +			regulator-name = "Dummy";
> > +			/* Dummy N/C */
> > +			gpio = <&gpio TEGRA_GPIO(V, 7)
> > GPIO_ACTIVE_HIGH>;
> This is wrong. If that GPIO isn't actually part of the backlight, the
> DT?
> should not say that it is. The gpio property is optional according
> to?
> the DT binding documentation, so this shouldn't be needed.


Well, I guess then it's lying. If I leave it away I get the following:

stdio_add_devices: Video device failed (ret=-38)

And it won't quite work.