linux-kernel - Re: [PATCH 1/2] dt-bindings: display: bridge: Add NXP i.MX93 parallel display format configuration

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Date:   Sun, 29 Jan 2023 12:46:47 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Liu Ying <victor.liu@....com>, dri-devel@...ts.freedesktop.org,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Cc:     andrzej.hajda@...el.com, neil.armstrong@...aro.org,
        robert.foss@...aro.org, Laurent.pinchart@...asonboard.com,
        jonas@...boo.se, jernej.skrabec@...il.com, airlied@...il.com,
        daniel@...ll.ch, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, shawnguo@...nel.org,
        s.hauer@...gutronix.de, kernel@...gutronix.de, festevam@...il.com,
        linux-imx@....com
Subject: Re: [PATCH 1/2] dt-bindings: display: bridge: Add NXP i.MX93 parallel
 display format configuration

On 28/01/2023 04:47, Liu Ying wrote:
> NXP i.MX93 mediamix blk-ctrl contains one DISPLAY_MUX register which
> configures parallel display format by using the "PARALLEL_DISP_FORMAT"
> field. Add device tree bindings for the display format configuration.
> 
> Signed-off-by: Liu Ying <victor.liu@....com>
> ---
>  .../display/bridge/nxp,imx93-pdfc.yaml        | 78 +++++++++++++++++++
>  1 file changed, 78 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/display/bridge/nxp,imx93-pdfc.yaml
> 
> diff --git a/Documentation/devicetree/bindings/display/bridge/nxp,imx93-pdfc.yaml b/Documentation/devicetree/bindings/display/bridge/nxp,imx93-pdfc.yaml
> new file mode 100644
> index 000000000000..a84bfb46b01d
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/display/bridge/nxp,imx93-pdfc.yaml
> @@ -0,0 +1,78 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/display/bridge/nxp,imx93-pdfc.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: NXP i.MX93 Parallel Display Format Configuration
> +
> +maintainers:
> +  - Liu Ying <victor.liu@....com>
> +
> +description: |
> +  The i.MX93 mediamix blk-ctrl contains one DISPLAY_MUX register which
> +  configures parallel display format by using the "PARALLEL_DISP_FORMAT"
> +  field.
> +
> +properties:
> +  compatible:
> +    const: nxp,imx93-pdfc


Based on description, I have doubts this is a separate bridge device.
Why this is not part of display driver/bindings?

We do not create usually devices for single registers, because they are
not a devices. Devices are a bit more complex - have some pin
inputs/outputs, not a register only. Of course there are exception, but
this one does not look like one.

> +
> +  reg:
> +    maxItems: 1

Your driver tells different story:

syscon_node_to_regmap(dev->of_node->parent);

(which also points to fact this is not a separate device)

Best regards,
Krzysztof