linux-kernel - Re: [PATCH v3 3/3] ARM: dts: stm32: fix several DT warnings on stm32mp15

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Date:   Thu, 18 May 2023 01:33:57 +0200
From:   Marek Vasut <marex@...x.de>
To:     Raphael Gallais-Pou <raphael.gallais-pou@...s.st.com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        Philippe Cornu <philippe.cornu@...s.st.com>,
        Yannick Fertre <yannick.fertre@...s.st.com>
Cc:     dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
        linux-stm32@...md-mailman.stormreply.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kernel@...electronics.com
Subject: Re: [PATCH v3 3/3] ARM: dts: stm32: fix several DT warnings on
 stm32mp15

On 5/17/23 19:04, Raphael Gallais-Pou wrote:
> Hi Marek

Hi,

> On 5/17/23 17:41, Marek Vasut wrote:
>> On 5/17/23 16:35, Raphael Gallais-Pou wrote:
>>
>> Hi,
>>
>>> diff --git a/arch/arm/boot/dts/stm32mp15xx-dkx.dtsi
>>> b/arch/arm/boot/dts/stm32mp15xx-dkx.dtsi
>>> index 0f1110e42c93..a6e2e20f12fa 100644
>>> --- a/arch/arm/boot/dts/stm32mp15xx-dkx.dtsi
>>> +++ b/arch/arm/boot/dts/stm32mp15xx-dkx.dtsi
>>> @@ -457,8 +457,7 @@ &ltdc {
>>>        status = "okay";
>>>          port {
>>> -        ltdc_ep0_out: endpoint@0 {
>>> -            reg = <0>;
>>> +        ltdc_ep0_out: endpoint {
>>>                remote-endpoint = <&sii9022_in>;
>>>            };
>>>        };
>>
>> This LTDC port/endpoint stuff always scares me, because I always feel I get it
>> wrong.
>>
>> I believe the LTDC does have one "port" , correct.
>>
>> But I think (?) that the LTDC has two endpoints, endpoint@0 for DPI (parallel
>> output out of the SoC) and endpoint@1 for DSI (internal connection into the
>> DSI serializer) ?
> 
> You are correct indeed, I rushed the patch and did not thought about this. I
> agree that this can be confusing, as I also take some time to think through it.
> 
>>
>> Only one of the endpoints can be connected at a time, but there are actually
>> two endpoints in the LTDC port {} node, aren't there ?
> Yes, they are mutually exclusive.
>>
>> So the original description should be OK I think , maybe #address/#size-cells
>> are missing instead ?
> 
> Thing is: this file is only included in two device-trees : stm32mp157c-dk1.dts
> and stm32mp157c-dk2.dts.
> 
> Among those two files there is only one which adds a second endpoint. Thus if
> the fields are set higher in the hierarchy, a warning yields.

I do not understand this one part, which warning are you trying to fix ?
I just ran '$ make CHECK_DTBS=1 stm32mp157a-dk1.dtb stm32mp157c-dk2.dtb' 
in latest linux-next and there was no warning related to LTDC .

I think if you retain the stm32mp151.dtsi &ltdc { port { #address-cells 
= <1>; #size-cells = <0>; }; }; part, then you wouldn't be getting any 
warnings regarding LTDC , and you wouldn't have to remove the 
unit-address from endpoint@0 .

btw. I do use both endpoint@...ndpoint@1 in Avenger96 DTOs, but those 
are not submitted yet, I have to clean them up a bit more first.

> One way to do it would be to make the endpoint@0 go down in the device-tree with
> its dependencies, so that both endpoints are the same level without generating
> noise.

I'm afraid I really don't quite understand which warning you're 
referring to. Can you please share that warning and ideally how to 
trigger it (the command-line incantation) ?

-- 
Best regards,
Marek Vasut