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

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Date:   Thu, 15 Apr 2021 16:30:38 +0200
From:   Marek Vasut <marex@...x.de>
To:     Alexandre TORGUE <alexandre.torgue@...s.st.com>, arnd@...db.de,
        robh+dt@...nel.org, jagan@...rulasolutions.com,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        Marcin Sloniewski <marcin.sloniewski@...il.com>,
        Ahmad Fatoum <a.fatoum@...gutronix.de>
Cc:     linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-stm32@...md-mailman.stormreply.com,
        linux-kernel@...r.kernel.org, Lee Jones <lee.jones@...aro.org>,
        kuba@...nel.org
Subject: Re: [PATCH 11/13] ARM: dts: stm32: fix LTDC port node on STM32 MCU ad
 MPU

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.