Re: [PATCH 1/5] dt-bindings: display: panel: mipi-dbi-spi: Add a pixel format property

From: Rob Herring
Date: Tue May 07 2024 - 16:28:58 EST


On Tue, May 07, 2024 at 11:57:26AM +0200, Noralf Trønnes wrote:
> The MIPI DBI 2.0 specification (2005) lists only two pixel formats for
> the Type C Interface (SPI) and that is 3-bits/pixel RGB111 with
> 2 options for bit layout.
>
> For Type A and B (parallel) the following formats are listed: RGB332,
> RGB444, RGB565, RGB666 and RGB888 (some have 2 options for the bit layout).
>
> Many MIPI DBI compatible controllers support all interface types on the
> same chip and often the manufacturers have chosen to provide support for
> the Type A/B interface pixel formats also on the Type C interface.
>
> Some chips provide many pixel formats with optional bit layouts over SPI,
> but the most common by far are RGB565 and RGB666. So even if the
> specification doesn't list these formats for the Type C interface, the
> industry has chosen to include them.
>
> The MIPI DCS specification lists the standard commands that can be sent
> over the MIPI DBI interface. The set_address_mode (36h) command has one
> bit in the parameter that controls RGB/BGR order:
> This bit controls the RGB data latching order transferred from the
> peripheral’s frame memory to the display device.
> This means that each supported RGB format also has a BGR variant.
>
> Based on this rationale document the following pixel formats describing
> the bit layout going over the wire:
> - RGB111 (option 1): x2r1g1b1r1g1b1 (2 pixels per byte)
> - BGR111 (option 1): x2b1g1r1b1g1r1 (2 pixels per byte)
> - RGB111 (option 2): x1r1g1b1x1r1g1b1 (2 pixels per byte)
> - BGR111 (option 2): x1b1g1r1x1b1g1r1 (2 pixels per byte)
> - RGB565: r5g6b5 (2 bytes)
> - BGR565: b5g6r5 (2 bytes)
> - RGB666: r6x2g6x2b6x2 (3 bytes)
> - BGR666: b6x2g6x2r6x2 (3 bytes)
> (x: don't care)
>
> Signed-off-by: Noralf Trønnes <noralf@xxxxxxxxxxx>
> ---
> .../bindings/display/panel/panel-mipi-dbi-spi.yaml | 31 ++++++++++++++++++++++
> 1 file changed, 31 insertions(+)
>
> diff --git a/Documentation/devicetree/bindings/display/panel/panel-mipi-dbi-spi.yaml b/Documentation/devicetree/bindings/display/panel/panel-mipi-dbi-spi.yaml
> index e808215cb39e..dac8f9af100e 100644
> --- a/Documentation/devicetree/bindings/display/panel/panel-mipi-dbi-spi.yaml
> +++ b/Documentation/devicetree/bindings/display/panel/panel-mipi-dbi-spi.yaml
> @@ -50,6 +50,12 @@ description: |
> | Command or data |
> |<D7><D6><D5><D4><D3><D2><D1><D0>|
>
> + The standard defines one pixel format for type C: RGB111. The industry
> + however has decided to provide the type A/B interface pixel formats also on
> + the Type C interface and most common among these are RGB565 and RGB666.
> + The MIPI DCS command set_address_mode (36h) has one bit that controls RGB/BGR
> + order. This gives each supported RGB format a BGR variant.
> +
> 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
> @@ -90,6 +96,29 @@ properties:
>
> spi-3wire: true
>
> + format:
> + description: >
> + Pixel format in bit order as going on the wire:
> + * `x2r1g1b1r1g1b1` - RGB111, 2 pixels per byte
> + * `x2b1g1r1b1g1r1` - BGR111, 2 pixels per byte
> + * `x1r1g1b1x1r1g1b1` - RGB111, 2 pixels per byte
> + * `x1b1g1r1x1b1g1r1` - BGR111, 2 pixels per byte
> + * `r5g6b5` - RGB565, 2 bytes
> + * `b5g6r5` - BGR565, 2 bytes
> + * `r6x2g6x2b6x2` - RGB666, 3 bytes
> + * `b6x2g6x2r6x2` - BGR666, 3 bytes
> + This property is optional for backwards compatibility and `r5g6b5` is
> + assumed in its absence.

Use schemas, not free form text:

default: r5g6b5

> + enum:
> + - x2r1g1b1r1g1b1
> + - x2b1g1r1b1g1r1
> + - x1r1g1b1x1r1g1b1
> + - x1b1g1r1x1b1g1r1
> + - r5g6b5
> + - b5g6r5
> + - r6x2g6x2b6x2
> + - b6x2g6x2r6x2
> +
> required:
> - compatible
> - reg
> @@ -116,6 +145,8 @@ examples:
> reset-gpios = <&gpio 25 GPIO_ACTIVE_HIGH>;
> write-only;
>
> + format = "r5g6b5";
> +
> backlight = <&backlight>;
>
> width-mm = <35>;
>
> --
> 2.45.0
>