[PATCH v3 1/3] dt-bindings: display: add bindings for MIPI DBI compatible SPI panels

[Maxime Ripard]

On Fri, Feb 11, 2022 at 02:04:32PM +0100, Noralf Trønnes wrote:
> Add binding for MIPI DBI compatible SPI panels.
> 
> 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)
> 
> Signed-off-by: Noralf Trønnes <noralf at tronnes.org>
> ---
>  .../display/panel/panel-mipi-dbi-spi.yaml     | 124 ++++++++++++++++++
>  1 file changed, 124 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..4d017a36ad4d
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/display/panel/panel-mipi-dbi-spi.yaml
> @@ -0,0 +1,124 @@
> +# 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:
> +    contains:
> +      const: panel-dbi-spi

This could be further improved by using

properties:
  compatible:
    items:
      - {} # Panel Specific Compatible
      - const: panel-dbi-spi

To make it obvious we expect two compatible, and what the first one should be.

Once fixed,

Acked-by: Maxime Ripard <maxime at cerno.tech>

Maxime
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