Re: [PATCH 11/13] ARM: dts: stm32: fix LTDC port node on STM32 MCU ad MPU

[Marek Vasut <marex@xxxxxxx>]

On 4/15/21 4:35 PM, Alexandre TORGUE wrote:
> On 4/15/21 4:30 PM, Marek Vasut wrote:
> > On 4/15/21 3:34 PM, Alexandre TORGUE wrote:
> > > Hi Marek
> >
> > Hello Alexandre,
> >
> > > > > diff --git a/arch/arm/boot/dts/stm32mp157c-dk2.dts 
> > > > > b/arch/arm/boot/dts/stm32mp157c-dk2.dts
> > > > > index 2bc92ef3aeb9..19ef475a48fc 100644
> > > > > --- a/arch/arm/boot/dts/stm32mp157c-dk2.dts
> > > > > +++ b/arch/arm/boot/dts/stm32mp157c-dk2.dts
> > > > > @@ -82,9 +82,15 @@
> > > > >   };
> > > > >   &ltdc {
> > > > > -    status = "okay";
> > > > > -
> > > > >       port {
> > > > > +        #address-cells = <1>;
> > > > > +        #size-cells = <0>;
> > > > > +
> > > > > +        ltdc_ep0_out: endpoint@0 {
> > > > > +            reg = <0>;
> > > > > +            remote-endpoint = <&sii9022_in>;
> > > > > +        };
> > > > > +
> > > > >           ltdc_ep1_out: endpoint@1 {
> > > > >               reg = <1>;
> > > > >               remote-endpoint = <&dsi_in>;
> > > >
> > > > [...]
> > > >
> > > > > diff --git a/arch/arm/boot/dts/stm32mp15xx-dhcor-avenger96.dtsi 
> > > > > b/arch/arm/boot/dts/stm32mp15xx-dhcor-avenger96.dtsi
> > > > > index 64dca5b7f748..e7f10975cacf 100644
> > > > > --- a/arch/arm/boot/dts/stm32mp15xx-dhcor-avenger96.dtsi
> > > > > +++ b/arch/arm/boot/dts/stm32mp15xx-dhcor-avenger96.dtsi
> > > > > @@ -277,11 +277,7 @@
> > > > >       status = "okay";
> > > > >       port {
> > > > > -        #address-cells = <1>;
> > > > > -        #size-cells = <0>;
> > > > > -
> > > > > -        ltdc_ep0_out: endpoint@0 {
> > > > > -            reg = <0>;
> > > > > +        ltdc_ep0_out: endpoint {
> > > > >               remote-endpoint = <&adv7513_in>;
> > > > >           };
> > > > >       };
> > > >
> > > > I think this is wrong, the AV96 can have two displays connected to 
> > > > two ports of the LTDC, just like DK2 for example.
> > >
> > > As for dk2 address/size cells are added only if there are 2 
> > > endpoints. It is for this reason I moved endpoint0 definition from 
> > > stm32mp15xx-dkx to stm32mp151a-dk1.dts (dk1 has only one endpoint).
> > >
> > > Here it's the same, if you have second endpoint then adress/size will 
> > > have to be added.
> >
> > That's a bit problematic. Consider either the use case of DTO which 
> > adds the other display, or even a custom board DTS. Without your 
> > patch, this works:
> >
> > arch/arm/boot/dts/stm32mp15xx-dhcor-avenger96.dtsi
> > &ltdc {
> >    ...
> >    ports {
> >      ltdc_ep0_out: endpoint@0 {
> >        remote-endpoint = <&adv7513_in>;
> >      };
> >    };
> > };
> >
> > board-with-display.dts or board-overlay.dts
> > &ltdc {
> >    ports {
> >      endpoint@1 { // just add another endpoint@1, no problem
> >        remote-endpoint = <&display>;
> >      };
> >    };
> > };
> >
> > With your patch, the DTS would have to modify the "endpoint" node to 
> > be "endpoint@0" probably with a whole lot of /detele-node/ etc. magic 
> > (DTO cannot do that, so that's a problem, and I do use DTOs on AV96 
> > extensively for the various expansion cards) and then add the 
> > endpoint@1. That becomes real complicated in custom board DT, and 
> > impossible with DTO.
>
> Yes I agree that it'll be problematic. So maybe so solution would be to 
> not detect a warning for the initial case (only one endpoint with a reg)

That looks OK. Or even better, if the checker warned only on IPs which 
cannot have more than one endpoint, but have endpoint@N in DT (where N 
in 0..+inf) . On IPs which can have one or more endpoints, the warning 
should not be emitted.