[U-Boot] [PATCH v1 3/5] colibri_t20: fix display configuration

[Marcel Ziswiler]

On Wed, 2016-09-14 at 17:19 +0000, Stephen Warren wrote:
> On 09/14/2016 09:20 AM, Marcel Ziswiler wrote:
> > 
> > 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.
> > 
> > > 
> > > > 
> > > > +			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.
> Does "it" mean the binding? Please note that the binding defines how
> the 
> DT should be structured and how code interpreting the DT should
> operate. 
> The binding isn't derived from the code, but rather the code is
> derived 
> from the binding.

In theory I agree but in practical speak this is wishful thinking as we
just first handedly saw now.

>  > If I leave it away I get the following:
> > 
> > 
> > stdio_add_devices: Video device failed (ret=-38)
> > 
> > And it won't quite work.
> That sounds like a bug in the U-Boot regulator driver. I believe you 
> should fix that, rather than working around the bug in DT.


Yes, I am pretty sure it won't be the last bug I uncover.
Unfortunately right now I do not feel like fixing all of U-Boot. This
series just tries to fix a very few select things (e.g. display and
USB) which used to work just fine before some bigger agendas came along
and broke them.