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

Stephen Warren
2016-09-12T18:18:37Z

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.

> 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.

> + 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.