linux-kernel - Re: [PATCH 2/3] dt-bindings: display: sitronix,st7920: Add DT schema

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Message-ID: <a211c028-b6f4-4f0f-9dea-842eff201c8f@kernel.org>
Date: Thu, 7 Aug 2025 10:09:06 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Iker Pedrosa <ikerpedrosam@...il.com>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>,
 Javier Martinez Canillas <javierm@...hat.com>
Cc: linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
 devicetree@...r.kernel.org
Subject: Re: [PATCH 2/3] dt-bindings: display: sitronix,st7920: Add DT schema

On 06/08/2025 14:48, Iker Pedrosa wrote:
> +title: Sitronix ST7920 LCD Display Controllers
> +
> +maintainers:
> +  - Iker Pedrosa <ikerpedrosam@...il.com>
> +
> +description: |

Do not need '|' unless you need to preserve formatting.

> +  The Sitronix ST7920 is a controller for monochrome dot-matrix graphical LCDs,
> +  most commonly used for 128x64 pixel displays.
> +  This binding supports connecting the display via a standard SPI bus.

Drop last sentence. You should write complete bindings for complete
hardware. Binding cannot support something and should not cover only one
bus.

> +
> +properties:
> +  compatible:
> +    const: sitronix,st7920
> +
> +  reg:
> +    description: The chip-select number for the device on the SPI bus.
> +    maxItems: 1
> +
> +  spi-max-frequency:
> +    description: Maximum SPI clock frequency in Hz.
> +    maximum: 600000
> +
> +  spi-cs-high:
> +    type: boolean
> +    description: Indicates the chip select is active high.

No supplies?

> +
> +required:
> +  - compatible
> +  - reg
> +  - spi-max-frequency

Missing allOf: with ref to spi properties

> +
> +additionalProperties: false

And this is unevaluatedProperties. Please look at other examples of
devices like that.

> +
> +examples:
> +  - |
> +    // Example: ST7920 connected to an SPI bus
> +    #include <dt-bindings/gpio/gpio.h>
> +
> +    spi0 {

spi {

> +        #address-cells = <1>;
> +        #size-cells = <0>;
> +
> +        display@0 {
> +            compatible = "sitronix,st7920";
> +            reg = <0>; // Chip select 0

Drop comment, obvious.

> +            spi-max-frequency = <600000>;
> +            spi-cs-high;
> +        };
> +    };
> 


Best regards,
Krzysztof