Re: [PATCH v2 02/14] dt-bindings: display: Add Solomon SSD16xx e-paper controller binding

[Krzysztof Kozlowski <krzk@kernel.org>]

On Sun, Sep 27, 2026 at 11:53:17PM +0530, Devarsh Thakkar wrote:
> Add device tree binding for the Solomon Systech SSD16xx family of e-Paper
> display controllers (SSD1683 [1], SSD1673 [3], SSD1680 [4], SSD1681 [5]).
> 

A nit, subject: drop second/last, redundant "binding". The
"dt-bindings" prefix is already stating that these are bindings.
See also:
https://elixir.bootlin.com/linux/v7.1-rc7/source/Documentation/devicetree/bindings/submitting-patches.rst#L23

> The binding covers the 4-wire SPI interface with required GPIO pins for
> reset (active-low), busy status (active-high), and data/command selection.
> The spi-max-frequency is capped at 20 MHz per the SSD1683 datasheet [1]
> which is also the maximum supported frequency amongst the family.
> 
> An optional rotation property allows static display orientation to be
> configured from device tree.
> 
> The data/command selection GPIO pin is also kept as optional since various
> SSD16XX controllers such as SSD1683 [1] support 3-wire mode too with
> data/command selection bit transmitted as first bit before sending the data
> sequence.
> 
> The first supported compatible is for Gooddisplay GDEY042T81 which is 4.2",
> 400x300 resolution black/white e-paper display using SSD1683 controller.
> 
> Links:
> [1] : https://www.crystalfontz.com/controllers/SolomonSystech/SSD1683
> [2] : https://files.seeedstudio.com/wiki/Other_Display/42-epaper/GDEY042T81.pdf
> [3] : https://www.crystalfontz.com/controllers/SolomonSystech/SSD1673
> [4] : https://www.crystalfontz.com/controllers/SolomonSystech/SSD1680
> [5] : https://www.crystalfontz.com/controllers/SolomonSystech/SSD1681
> 
> Signed-off-by: Devarsh Thakkar <devarsht@ti.com>
> ---
> Changes from v1:
>   - Added fallback compatible for the controller
>   - Wrap lines to 80
> 
>  .../bindings/display/solomon,ssd16xx.yaml     | 87 +++++++++++++++++++
>  1 file changed, 87 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/display/solomon,ssd16xx.yaml
> 
> diff --git a/Documentation/devicetree/bindings/display/solomon,ssd16xx.yaml b/Documentation/devicetree/bindings/display/solomon,ssd16xx.yaml
> new file mode 100644
> index 000000000000..b31fb862de04
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/display/solomon,ssd16xx.yaml

Filename must match compatible.

> @@ -0,0 +1,87 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/display/solomon,ssd16xx.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Solomon Systech SSD16xx controller based e-paper display panels
> +
> +maintainers:
> +  - Devarsh Thakkar <devarsht@ti.com>
> +
> +description:
> +  The SSD16xx family includes e-paper display controllers (SSD1673,
> +  SSD1680, SSD1681, SSD1683, SSD1677) with integrated gate driver,
> +  source driver and timing controller. Different panels use these
> +  controllers in monochrome or 3-color (black/white/red) configurations.
> +  The controller uses a 4-wire SPI interface and requires GPIO pins for
> +  reset, busy status, and data/command control. A 3-wire mode is also
> +  available where the D/C bit is transmitted along the SPI data line
> +  before each byte.
> +
> +allOf:
> +  - $ref: /schemas/spi/spi-peripheral-props.yaml#
> +
> +properties:
> +  compatible:
> +    items:
> +      - enum:
> +          # Good Display 4.2" 400x300 monochrome e-ink panel
> +          - gooddisplay,gdey042t81
> +      - enum:

No, fallback cannot be enumeration.

> +          - solomon,ssd1683
> +
> +  reg:
> +    maxItems: 1
> +
> +  spi-max-frequency:
> +    maximum: 20000000
> +
> +  reset-gpios:
> +    maxItems: 1
> +    description:
> +      GPIO connected to the RSTB (reset) pin. Active low.
> +
> +  busy-gpios:
> +    maxItems: 1
> +    description:
> +      GPIO connected to the BUSY pin. Active high when the controller
> +      is busy updating the display.
> +
> +  dc-gpios:
> +    maxItems: 1
> +    description:
> +      GPIO connected to the D/C (Data/Command) pin. Low for command,
> +      high for data.
> +
> +  rotation:
> +    $ref: /schemas/types.yaml#/definitions/uint32
> +    enum: [0, 90, 180, 270]
> +    description:
> +      Display rotation in degrees clockwise.
> +

Is this display controller or panel? If panel, then missing ref to
panel-common. If display controller, then description is misleading.

Best regards,
Krzysztof