Message-ID: <4fed02bb-3f10-4694-800a-484d76833414@ti.com>
Date:   Fri, 13 Oct 2023 10:38:42 +0530
From:   Jayesh Choudhary <j-choudhary@...com>
To:     <robh+dt@...nel.org>, <krzysztof.kozlowski+dt@...aro.org>,
        <vigneshr@...com>, <nm@...com>, <rogerq@...nel.org>,
        Andrew Davis <afd@...com>, Aradhya Bhatia <a-bhatia1@...com>
CC:     Tomi Valkeinen <tomi.valkeinen@...asonboard.com>,
        <s-vadapalli@...com>, <kristo@...nel.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>
Subject: Re: [PATCH v9 4/5] arm64: dts: ti: k3-j784s4-evm: Enable
 DisplayPort-0


On 08/08/23 00:24, Andrew Davis wrote:
> On 8/7/23 1:29 PM, Aradhya Bhatia wrote:
>>
>>
>> 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.
>>
> 
> Ah, I see now.
> 
> Almost seems like a bug in dtc checks, but checking the code it
> looks deliberate, although I cannot see why..
> 
> Rob,
> 
> Could you provide some guidance on why graph nodes are handled
> this way? Seems this is valid:
> 
> ports {
>      #address-cells = <1>;
>      #size-cells = <0>;
> 
>      port@1 {
>          reg = <1>;
>      };
> }
> 
> but this is not:
> 
> ports {
>      #address-cells = <1>;
>      #size-cells = <0>;
> 
>      port@0 {
>          reg = <0>;
>      };
> };
> 
> I'm guessing we allow port 0 to not be numbered if it is the only
> one for legacy convenience, but *forcing* it to not be numbered
> when it would otherwise be more consistent seems overly strict.
> 
> Andrew

Hello Rob, Krzysztof,

For this series, v11 has been already reviewed by Roger and Aradhya:
<https://lore.kernel.org/all/77701023-7bd1-4e04-aa44-0e46aa087c4f@kernel.org/>

Only this warning persist. Can you ACK the series so that it can
be queued/merged.
If W=1 warning is not acceptable, I can revert to port description
here in v9.

Warm Regards,
Jayesh



> 
>> 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>;
>>>>>
>>>>>
>>>>> [...]
>>>>
>>

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