dt-bindings: display: add bindings for MIPI DBI compatible SPI panels

# 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@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@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>;

                vactive = <128>;

                hback-porch = <0>;

                vback-porch = <0>;

                clock-frequency = <0>;

                hfront-porch = <0>;

                hsync-len = <0>;

                vfront-porch = <0>;

                vsync-len = <0>;

            };

        };

    };

...