Re: [PATCH 1/4] dt-bindings: display: panel: document panel-id

Sam Ravnborg
2019-12-07T21:13:57Z

On Sat, Dec 07, 2019 at 12:35:50PM -0800, Rob Clark wrote:
> From: Rob Clark <robdclark@chromium.org>
>
> For devices that have one of several possible panels installed, the
> panel-id property gives firmware a generic way to locate and enable the
> panel node corresponding to the installed panel.

For display timings there is something similar.
Here the property is named native-mode and is a phandle to the
preferred timing.
And it is documented that if no native-mode is specified the first
timing in the tree is chosen.
So a different concept than this.

I could not from your otherwise well-documented changelog see why you
wanted to go for an opauge integer and status rather than a phandle to
the active display.

The panel-id, if I get it right, is optional and the important part is
that the first panel with staus = "okay" is selected.
This would cover my usecase fine.
I have a target with four different displays and the bootloader
knows what display is used (based on gpio etc).
The bootloader (barebox in my case) uses a simple variant of the DT,
but reads in the DT used by the kernel and can modify the DT before
it is passed to the kernel.

Sam

> Example of how to use this property:
>
> ivo_panel {
> compatible = "ivo,m133nwf4-r0";
> panel-id = <0xc5>;
> status = "disabled";
>
> ports {
> port {
> ivo_panel_in_edp: endpoint {
> remote-endpoint = <&sn65dsi86_out_ivo>;
> };
> };
> };
> };
>
> boe_panel {
> compatible = "boe,nv133fhm-n61";
> panel-id = <0xc4>;
> status = "disabled";
>
> ports {
> port {
> boe_panel_in_edp: endpoint {
> remote-endpoint = <&sn65dsi86_out_boe>;
> };
> };
> };
> };
>
> sn65dsi86: bridge@2c {
> compatible = "ti,sn65dsi86";
>
> ports {
> #address-cells = <1>;
> #size-cells = <0>;
>
> port@0 {
> reg = <0>;
> sn65dsi86_in_a: endpoint {
> remote-endpoint = <&dsi0_out>;
> };
> };
>
> port@1 {
> reg = <1>;
>
> sn65dsi86_out_boe: endpoint@c4 {
> remote-endpoint = <&boe_panel_in_edp>;
> };
>
> sn65dsi86_out_ivo: endpoint@c5 {
> remote-endpoint = <&ivo_panel_in_edp>;
> };
> };
> };
> };
>
> Signed-off-by: Rob Clark <robdclark@chromium.org>
> ---
> .../bindings/display/panel/panel-common.yaml | 26 +++++++++++++++++++
> 1 file changed, 26 insertions(+)
>
> diff --git a/Documentation/devicetree/bindings/display/panel/panel-common.yaml b/Documentation/devicetree/bindings/display/panel/panel-common.yaml
> index ef8d8cdfcede..6113319b91dd 100644
> --- a/Documentation/devicetree/bindings/display/panel/panel-common.yaml
> +++ b/Documentation/devicetree/bindings/display/panel/panel-common.yaml
> @@ -75,6 +75,32 @@ properties:
> in the device graph bindings defined in
> Documentation/devicetree/bindings/graph.txt.
>
> + panel-id:
> + description:
> + To support the case where one of several different panels can be installed
> + on a device, the panel-id property can be used by the firmware to identify
> + which panel should have it's status changed to "ok". This property is not
> + used by the HLOS itself.
> +
> + For a device with multiple potential panels, a node for each potential
> + should be defined with status = "disabled", and an appropriate panel-id
> + property. The video data producer should be setup with endpoints going to
> + each possible panel. The firmware will find the dt node with a panel-id
> + matching the actual panel installed, and change it's status to "ok".
> +
> + The exact method the firmware uses to determine the panel-id of the installed
> + panel is outside the scope of this binding, but a few examples are
> +
> + 1) u-boot module reading a value from a u-boot env var
> + 2) EFI driver module reading a value from an EFI variable
> + 3) device specific firmware reading some device specific GPIOs or
> + e-fuse
> +
> + The panel-id values are an opaque integer. They can be sparse. The only
> + important thing is that each possible panel in the system has a unique
> + panel-id, and that the values configured in the device's DTB match the
> + values that the firmware is looking for.
> +
> ddc-i2c-bus:
> $ref: /schemas/types.yaml#/definitions/phandle
> description:
> --
> 2.23.0
>
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