Re: [PATCH 1/3] dt-bindings: display: add bindings for MIPI DBI compatible SPI panels

[Rob Herring <robh+dt@xxxxxxxxxx>]

On Sun, Jan 23, 2022 at 11:25 AM Noralf Trønnes <noralf@xxxxxxxxxxx> wrote:
>
> Add binding for MIPI DBI compatible SPI panels.

I'm sure we already have MIPI DBI panels. What's this for?

>
> Signed-off-by: Noralf Trønnes <noralf@xxxxxxxxxxx>
> ---
>  .../display/panel/panel-mipi-dbi-spi.yaml     | 69 +++++++++++++++++++
>  1 file changed, 69 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/display/panel/panel-mipi-dbi-spi.yaml
>
> diff --git a/Documentation/devicetree/bindings/display/panel/panel-mipi-dbi-spi.yaml b/Documentation/devicetree/bindings/display/panel/panel-mipi-dbi-spi.yaml
> new file mode 100644
> index 000000000000..d6c8accb045c
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/display/panel/panel-mipi-dbi-spi.yaml
> @@ -0,0 +1,69 @@
> +# SPDX-License-Identifier: GPL-2.0-only
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/display/panel/panel-mipi-dbi-spi.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: MIPI DBI SPI Panels Device Tree Bindings
> +
> +maintainers:
> +  - Noralf Trønnes <noralf@xxxxxxxxxxx>
> +
> +description:
> +  This binding is for display panels using a MIPI DBI controller
> +  in SPI mode.
> +
> +allOf:
> +  - $ref: panel/panel-common.yaml#
> +  - $ref: /schemas/spi/spi-peripheral-props.yaml#
> +
> +properties:
> +  compatible:
> +    const: panel-mipi-dbi-spi

Does the MIPI spec define how to power on a DBI panel with regulators,
enable/reset lines, etc. and all the timing constraints between those?
If not, then this compatible on its own is useless. It's fine as a
fallback if it's presence means the panel uses only standard DBI
commands and no vendor specific commands.

> +
> +  model:
> +    $ref: /schemas/types.yaml#/definitions/string
> +    description: The name of the display panel.
> +
> +  write-only:
> +    type: boolean
> +    description:
> +      Controller is not readable (ie. MISO is not wired up).
> +
> +  dc-gpios:
> +    maxItems: 1
> +    description: |
> +      Controller data/command selection (D/CX) in 4-line SPI mode.
> +      If not set, the controller is in 3-line SPI mode.
> +
> +  backlight: true
> +  reg: true
> +  reset-gpios: true
> +
> +required:
> +  - compatible
> +  - model
> +  - reg
> +
> +additionalProperties: false
> +
> +examples:
> +  - |
> +    #include <dt-bindings/gpio/gpio.h>
> +
> +    spi {
> +            #address-cells = <1>;
> +            #size-cells = <0>;
> +
> +            display@0{
> +                    compatible = "panel-mipi-dbi-spi";
> +                    model = "sainsmart18";
> +                    reg = <0>;
> +                    spi-max-frequency = <40000000>;
> +                    dc-gpios = <&gpio 24 GPIO_ACTIVE_HIGH>;
> +                    reset-gpios = <&gpio 25 GPIO_ACTIVE_HIGH>;
> +                    write-only;
> +            };
> +    };
> +
> +...
> --
> 2.33.0
>