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

[Marek Vasut]

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@0/endpoint@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