[PATCH v5 1/5] dt-bindings: display: add bindings for MIPI DBI compatible SPI panels

[Rob Herring]

On Thu, Feb 24, 2022 at 04:27:04PM +0100, Noralf Trønnes wrote:
> Add binding for MIPI DBI compatible SPI panels.
> 
> v5:
> - Add sainsmart18 to compatible items (Rob)
> - Expand write-only description (Sam)
> 
> v4:
> - There should only be two compatible (Maxime)
> - s/panel-dbi-spi/panel-mipi-dbi-spi/in compatible
> 
> v3:
> - Move properties to Device Tree (Maxime)
> - Use contains for compatible (Maxime)
> - Add backlight property to example
> - Flesh out description
> 
> v2:
> - Fix path for panel-common.yaml
> - Use unevaluatedProperties
> - Drop properties which are in the allOf section
> - Drop model property (Rob)
> 
> Acked-by: Maxime Ripard <maxime at cerno.tech>
> Acked-by: Sam Ravnborg <sam at ravnborg.org>
> Signed-off-by: Noralf Trønnes <noralf at tronnes.org>
> ---
>  .../display/panel/panel-mipi-dbi-spi.yaml     | 127 ++++++++++++++++++
>  1 file changed, 127 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..a054f65435ce
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/display/panel/panel-mipi-dbi-spi.yaml
> @@ -0,0 +1,127 @@
> +# SPDX-License-Identifier: (GPL-2.0-only or BSD-2-Clause)
> +%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 Panel
> +
> +maintainers:
> +  - Noralf Trønnes <noralf at tronnes.org>
> +
> +description: |
> +  This binding is for display panels using a MIPI DBI compatible controller
> +  in SPI mode.
> +
> +  The MIPI Alliance Standard for Display Bus Interface defines the electrical
> +  and logical interfaces for display controllers historically used in mobile
> +  phones. The standard defines 4 display architecture types and this binding is
> +  for type 1 which has full frame memory. There are 3 interface types in the
> +  standard and type C is the serial interface.
> +
> +  The standard defines the following interface signals for type C:
> +  - Power:
> +    - Vdd: Power supply for display module
> +    - Vddi: Logic level supply for interface signals
> +    Combined into one in this binding called: power-supply
> +  - Interface:
> +    - CSx: Chip select
> +    - SCL: Serial clock
> +    - Dout: Serial out
> +    - Din: Serial in
> +    - SDA: Bidrectional in/out
> +    - D/CX: Data/command selection, high=data, low=command
> +      Called dc-gpios in this binding.
> +    - RESX: Reset when low
> +      Called reset-gpios in this binding.
> +
> +  The type C interface has 3 options:
> +
> +    - Option 1: 9-bit mode and D/CX as the 9th bit
> +      |              Command              |  the next command or following data  |
> +      |<0><D7><D6><D5><D4><D3><D2><D1><D0>|<D/CX><D7><D6><D5><D4><D3><D2><D1><D0>|
> +
> +    - Option 2: 16-bit mode and D/CX as a 9th bit
> +      |              Command or data                              |
> +      |<X><X><X><X><X><X><X><D/CX><D7><D6><D5><D4><D3><D2><D1><D0>|
> +
> +    - Option 3: 8-bit mode and D/CX as a separate interface line
> +      |        Command or data         |
> +      |<D7><D6><D5><D4><D3><D2><D1><D0>|
> +
> +  The panel resolution is specified using the panel-timing node properties
> +  hactive (width) and vactive (height). The other mandatory panel-timing
> +  properties should be set to zero except clock-frequency which can be
> +  optionally set to inform about the actual pixel clock frequency.
> +
> +  If the panel is wired to the controller at an offset specify this using
> +  hback-porch (x-offset) and vback-porch (y-offset).
> +
> +allOf:
> +  - $ref: panel-common.yaml#
> +  - $ref: /schemas/spi/spi-peripheral-props.yaml#
> +
> +properties:
> +  compatible:
> +    items:
> +      - enum:
> +        - sainsmart18
> +      - const: panel-mipi-dbi-spi
> +
> +  write-only:
> +    type: boolean
> +    description:
> +      Controller is not readable (ie. Din (MISO on the SPI interface) 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.
> +
> +required:
> +  - compatible
> +  - reg
> +  - panel-timing
> +
> +unevaluatedProperties: false
> +
> +examples:
> +  - |
> +    #include <dt-bindings/gpio/gpio.h>
> +
> +    spi {
> +            #address-cells = <1>;
> +            #size-cells = <0>;
> +
> +            display at 0{
> +                    compatible = "sainsmart18", "panel-mipi-dbi-spi";
> +                    reg = <0>;
> +                    spi-max-frequency = <40000000>;
> +
> +                    dc-gpios = <&gpio 24 GPIO_ACTIVE_HIGH>;
> +                    reset-gpios = <&gpio 25 GPIO_ACTIVE_HIGH>;
> +                    write-only;
> +
> +                    backlight = <&backlight>;
> +
> +                    width-mm = <35>;
> +                    height-mm = <28>;
> +
> +                    panel-timing {
> +                        hactive = <160>;

The indentation is inconsistent here. I'd suggest using 4 spaces for 
each level.

With that and yamllint fix,

Reviewed-by: Rob Herring <robh at kernel.org>


> +                        vactive = <128>;
> +                        hback-porch = <0>;
> +                        vback-porch = <0>;
> +
> +                        clock-frequency = <0>;
> +                        hfront-porch = <0>;
> +                        hsync-len = <0>;
> +                        vfront-porch = <0>;
> +                        vsync-len = <0>;

0 doesn't make much sense here. 

If most of this is n/a and just populated to satisfy the schema, we 
should probably make all these optional. Anyway, that's a separate 
issue to address.

Rob