linux-kernel - Re: [PATCH v2 2/3] dt-bindings: arm: mediatek: mmsys: Add OF graph support for board path

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Date: Thu, 25 Apr 2024 02:23:58 +0000
From: CK Hu (胡俊光) <ck.hu@...iatek.com>
To: "angelogioacchino.delregno@...labora.com"
	<angelogioacchino.delregno@...labora.com>, "chunkuang.hu@...nel.org"
	<chunkuang.hu@...nel.org>
CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mediatek@...ts.infradead.org" <linux-mediatek@...ts.infradead.org>,
	"wenst@...omium.org" <wenst@...omium.org>, "devicetree@...r.kernel.org"
	<devicetree@...r.kernel.org>, "tzimmermann@...e.de" <tzimmermann@...e.de>,
	Shawn Sung (宋孝謙) <Shawn.Sung@...iatek.com>,
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	Jitao Shi (石记涛) <jitao.shi@...iatek.com>,
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	<matthias.bgg@...il.com>, Yu-chang Lee (李禹璋)
	<Yu-chang.Lee@...iatek.com>, "linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2 2/3] dt-bindings: arm: mediatek: mmsys: Add OF graph
 support for board path

Hi, Angelo:

On Tue, 2024-04-09 at 14:02 +0200, AngeloGioacchino Del Regno wrote:
> Document OF graph on MMSYS/VDOSYS: this supports up to three DDP
> paths
> per HW instance (so potentially up to six displays for multi-vdo
> SoCs).
> 
> The MMSYS or VDOSYS is always the first component in the DDP
> pipeline,
> so it only supports an output port with multiple endpoints - where
> each
> endpoint defines the starting point for one of the (currently three)
> possible hardware paths.
> 
> Signed-off-by: AngeloGioacchino Del Regno <
> angelogioacchino.delregno@...labora.com>
> ---
>  .../bindings/arm/mediatek/mediatek,mmsys.yaml | 23
> +++++++++++++++++++
>  1 file changed, 23 insertions(+)
> 
> diff --git
> a/Documentation/devicetree/bindings/arm/mediatek/mediatek,mmsys.yaml
> b/Documentation/devicetree/bindings/arm/mediatek/mediatek,mmsys.yaml
> index b3c6888c1457..4e9acd966aa5 100644
> ---
> a/Documentation/devicetree/bindings/arm/mediatek/mediatek,mmsys.yaml
> +++
> b/Documentation/devicetree/bindings/arm/mediatek/mediatek,mmsys.yaml
> @@ -93,6 +93,29 @@ properties:
>    '#reset-cells':
>      const: 1
>  
> +  port:
> +    $ref: /schemas/graph.yaml#/properties/port
> +    description:
> +      Output port node. This port connects the MMSYS/VDOSYS output
> to
> +      the first component of one display pipeline, for example one
> of
> +      the available OVL or RDMA blocks.
> +      Some MediaTek SoCs support up to three display outputs per
> MMSYS.
> +    properties:
> +      endpoint@0:
> +        $ref: /schemas/graph.yaml#/properties/endpoint
> +        description: Output to the primary display pipeline
> +
> +      endpoint@1:
> +        $ref: /schemas/graph.yaml#/properties/endpoint
> +        description: Output to the secondary display pipeline
> +
> +      endpoint@2:
> +        $ref: /schemas/graph.yaml#/properties/endpoint
> +        description: Output to the tertiary display pipeline
> +
> +    required:
> +      - endpoint@0
> +

mmsys/vdosys does not output data to the first component of display
pipeline, so this connection looks 'virtual'. Shall we add something
virtual in device tree? You add this in order to decide which pipeline
is 1st, 2nd, 3rd, but for device it don't care which one is first. In
computer, software could change which display is the primary display.
I'm not sure it's good to decide display order in device tree?

Regards,
CK


>  required:
>    - compatible
>    - reg