linux-kernel - Re: [PATCH v9 4/5] arm64: dts: ti: k3-j784s4-evm: Enable DisplayPort-0

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Message-ID: <435f9b99-b888-2e18-cf70-8c7d074b68be@ti.com>
Date:   Mon, 7 Aug 2023 23:59:31 +0530
From:   Aradhya Bhatia <a-bhatia1@...com>
To:     Andrew Davis <afd@...com>, Jayesh Choudhary <j-choudhary@...com>,
        <nm@...com>, <vigneshr@...com>
CC:     Tomi Valkeinen <tomi.valkeinen@...asonboard.com>,
        <s-vadapalli@...com>, <kristo@...nel.org>, <robh+dt@...nel.org>,
        <krzysztof.kozlowski+dt@...aro.org>, <conor+dt@...nel.org>,
        <r-ravikumar@...com>, <sabiya.d@...com>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>, <rogerq@...nel.org>
Subject: Re: [PATCH v9 4/5] arm64: dts: ti: k3-j784s4-evm: Enable
 DisplayPort-0



On 07-Aug-23 21:19, Andrew Davis wrote:
> On 8/7/23 7:56 AM, Aradhya Bhatia wrote:
>> Hi Jayesh,
>>
>> On 07-Aug-23 17:54, Jayesh Choudhary wrote:
>>> Hello Aradhya,
>>>
>>> Thank you for the review.
>>>
>>> On 05/08/23 00:52, Aradhya Bhatia wrote:
>>>> Hi Jayesh,
>>>>
>>>>
>>>> On 03-Aug-23 13:34, Jayesh Choudhary wrote:
>>>>> From: Rahul T R <r-ravikumar@...com>
>>>>>
>>>>> Enable display for J784S4 EVM.
>>>>>
>>>>> Add assigned clocks for DSS, DT node for DisplayPort PHY and pinmux
>>>>> for
>>>>> DP HPD. Add the clock frequency for serdes_refclk.
>>>>>
>>>>> Add the endpoint nodes to describe connection from:
>>>>> DSS => MHDP => DisplayPort connector.
>>>>>
>>>>> Also add the GPIO expander-4 node and pinmux for main_i2c4 which is
>>>>> required for controlling DP power. Set status for all required nodes
>>>>> for DP-0 as "okay".
>>>>>
>>>>> Signed-off-by: Rahul T R <r-ravikumar@...com>
>>>>> [j-choudhary@...com: move all the changes together to enable DP-0 in
>>>>> EVM]
>>>>> Signed-off-by: Jayesh Choudhary <j-choudhary@...com>
>>>>> ---
>>>>>    arch/arm64/boot/dts/ti/k3-j784s4-evm.dts | 119
>>>>> +++++++++++++++++++++++
>>>>>    1 file changed, 119 insertions(+)
>>>
>>> [...]
>>>
>>>>> +        reg = <0>;
>>>>> +        cdns,num-lanes = <4>;
>>>>> +        #phy-cells = <0>;
>>>>> +        cdns,phy-type = <PHY_TYPE_DP>;
>>>>> +        resets = <&serdes_wiz4 1>, <&serdes_wiz4 2>,
>>>>> +             <&serdes_wiz4 3>, <&serdes_wiz4 4>;
>>>>> +    };
>>>>> +};
>>>>> +
>>>>> +&mhdp {
>>>>> +    status = "okay";
>>>>> +    pinctrl-names = "default";
>>>>> +    pinctrl-0 = <&dp0_pins_default>;
>>>>> +    phys = <&serdes4_dp_link>;
>>>>> +    phy-names = "dpphy";
>>>>> +};
>>>>> +
>>>>> +&dss_ports {
>>>>> +    port {
>>>>
>>>> Port index has not been added here. Since this port outputs to MHDP
>>>> bridge, this should be "port@0", and a "reg = <0>;" property should be
>>>> added below (along with the address and size cells properties).
>>>>
>>>> I suppose this works functionally in this case, because the port gets
>>>> defaulted to "0" by the driver. But in future, when we add support for
>>>> other dss output(s) on j784s4-evm, the driver will need indices to
>>>> distinguish among them.
>>>>
>>>
>>> Okay. It makes sense.
>>> Just one thing here. Adding reg here would require it to have #address-
>>> cells and #size-cell but since we have only single child port that too
>>> at reg=<0>, it would throw dtbs_check warning:
>>>
>>> arch/arm64/boot/dts/ti/k3-j784s4-main.dtsi:1828.20-1831.5: Warning
>>> (graph_child_address): /bus@...000/dss@...0000/ports: graph node has
>>> single child node 'port@0', #address-cells/#size-cells are not necessary
>>>    also defined at arch/arm64/boot/dts/ti/k3-j784s4-evm.dts:911.12-919.3
>>>
>>
>> Okay! Was not aware about this. I still think "port@0" should be
>> specified instead of just "port" and the warning should be ignored, if
>> possible.
>>
> 
> Do not ignore new DT check warnings, if you go with "port@0" (which you
> need to do as the "ti,j721e-dss" binding requires it) you must also add
> the #address-cells/#size-cells.
> 

The warning that Jayesh mentioned above comes when "port@0" is
mentioned, *along-with* the #address-cells/#size-cells properties.
Essentially, it wants us to not use "port@0" when only single port is
being added whose reg values is 0.

This warning does not come when only a single port other than 0,
"port@1" for e.g., is being used. That's the warning, that should get
ignored, if possible.

However, just mentioning "port@0", without the #address-cells/
#size-cells, would be plain wrong.

Regards
Aradhya

> 
>> If there were only a "port@1" child node, this warning would not have
>> come up, and I believe "port@0" should be treated just the same.
>>
>> Moreover, while we can add these properties at a later stage as an
>> incremental patch, adding the size and address cells in the dtsi would
>> affect other platform dts files as well, that use this SoC.
>>
>> For e.g., the patch 5/5 of this series, on AM69-SK will still require
>> the size and address cells for its ports. The clean up then will be that
>> much more, when adding those incremental patches.
>>
>> Anyway, I will let Nishanth and Vignesh take the final call on this.
>>
>> Regards
>> Aradhya
>>
>>>
>>>>> +        dpi0_out: endpoint {
>>>>> +            remote-endpoint = <&dp0_in>;
>>>
>>>
>>> [...]
>>