linux-kernel - Re: [PATCH v4 2/3] dt-bindings: arm: mediatek: mmsys: Add OF graph support for board path

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Message-ID: <eea541cb-1917-44de-ae40-0824372baab8@collabora.com>
Date: Thu, 16 May 2024 11:42:51 +0200
From: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
To: CK Hu (胡俊光) <ck.hu@...iatek.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>,
 "mripard@...nel.org" <mripard@...nel.org>,
 Jitao Shi (石记涛) <jitao.shi@...iatek.com>,
 "daniel@...ll.ch" <daniel@...ll.ch>,
 "p.zabel@...gutronix.de" <p.zabel@...gutronix.de>,
 "conor+dt@...nel.org" <conor+dt@...nel.org>,
 "maarten.lankhorst@...ux.intel.com" <maarten.lankhorst@...ux.intel.com>,
 "robh@...nel.org" <robh@...nel.org>,
 "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
 "airlied@...il.com" <airlied@...il.com>,
 "krzysztof.kozlowski+dt@...aro.org" <krzysztof.kozlowski+dt@...aro.org>,
 "kernel@...labora.com" <kernel@...labora.com>,
 "matthias.bgg@...il.com" <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 v4 2/3] dt-bindings: arm: mediatek: mmsys: Add OF graph
 support for board path

Il 16/05/24 11:23, CK Hu (胡俊光) ha scritto:
> Hi, Angelo:
> 
> On Thu, 2024-05-16 at 10:11 +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.
>>
>> Reviewed-by: Rob Herring (Arm) <robh@...nel.org>
>> Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
>> ---
>>   .../bindings/arm/mediatek/mediatek,mmsys.yaml | 28 +++++++++++++++++++
>>   1 file changed, 28 insertions(+)
>>
>> diff --git a/Documentation/devicetree/bindings/arm/mediatek/mediatek,mmsys.yaml b/Documentation/devicetree/bindings/arm/mediatek/mediatek,mmsys.yaml
>> index b3c6888c1457..0ef67ca4122b 100644
>> --- a/Documentation/devicetree/bindings/arm/mediatek/mediatek,mmsys.yaml
>> +++ b/Documentation/devicetree/bindings/arm/mediatek/mediatek,mmsys.yaml
>> @@ -93,6 +93,34 @@ 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 multiple display outputs per MMSYS.
> 
> The display pipeline number usually depend on how many display interface. Display interface is in the end of pipeline.
> 

I have never stated that the display pipeline number depends on that.

Plus, the display interface is not described in the mmsys binding: this document
is only saying that mmsys' endpoint is to be connected to a (supported) component
of your choice. Nothing else.

> In below case, two RDMA is merged into one pipeline and output to one display interface DP_INTF. This is usually ONE display.
> 
> RDMA -+
>        Merge -> ... -> DP_INTF
> RDMA -+
> 
> In below case, one RDMA data output to two display interface DSI and DPI. This is usually TWO display with the same content.
> 
>                 +-> DSI
> RDMA -> ... -> +
>                 +-> DPI
> 

The actual content of a display is a software capability - if the hardware supports
that, and some MediaTek SoCs do, the connection does not happen at the endpoint of
mmsys, but later.

> So the display pipeline number does not depend on the number of first component. It usually depend on the number of display interface.
> 

I sure agree with that, but again, I have *never stated* that the display pipeline
number depends on the number of the first component.

> Regards,
> CK
> 
> 
>> +    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
>> +
>> +    oneOf:
>> +      - required:
>> +          - endpoint@0
>> +      - required:
>> +          - endpoint@1
>> +      - required:
>> +          - endpoint@2
>> +
>>   required:
>>     - compatible
>>     - reg