linux-kernel - Re: [PATCH v2 2/2] arm64: dts: meson-t7-a311d2-khadas-vim4: add initial device-tree

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Date:   Wed, 21 Jun 2023 08:37:02 +0100
From:   Lucas Tanure <tanure@...ux.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc:     Yixun Lan <dlan@...too.org>, Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Jerome Brunet <jbrunet@...libre.com>,
        Kevin Hilman <khilman@...libre.com>, Nick <nick@...das.com>,
        Artem <art@...das.com>, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-amlogic@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 2/2] arm64: dts: meson-t7-a311d2-khadas-vim4: add
 initial device-tree

On Wed, Jun 21, 2023 at 7:02 AM Krzysztof Kozlowski
<krzysztof.kozlowski@...aro.org> wrote:
>
> On 21/06/2023 00:09, Yixun Lan wrote:
> >> +            apb4: bus@...00000 {
> >> +                    compatible = "simple-bus";
> >> +                    reg = <0x0 0xfe000000 0x0 0x480000>;
> >> +                    #address-cells = <2>;
> >> +                    #size-cells = <2>;
> >> +                    ranges = <0x0 0x0 0x0 0xfe000000 0x0 0x480000>;
> >> +
> >> +                    uart_A: serial@...00 {
> >> +                            compatible = "amlogic,meson-t7-uart",
> >                                               ~~~~~~~~~~~~~~~~~
> > if you introduce new compatible string, then at least you need to document it
> > so Documentation/devicetree/bindings/serial/amlogic,meson-uart.yaml need to be updated
> >
> > but my qeustion here, why bother introducing new compatible string if nothing
> > changed with the compatible data? given the uart is same IP with g12a, can't we just
> > use "amlogic,meson-g12-uart" for this? no only it will reduce the structure length of
> > meson_uart_dt_match[], but also relieve maintainer's review burden?
>
> https://elixir.bootlin.com/linux/v6.1-rc1/source/Documentation/devicetree/bindings/writing-bindings.rst#L42
>
> Best regards,
> Krzysztof
>
Hi, I did not understand the recommendation here.
Can I add "amlogic,meson-t7-uart" without Documentation changes?
I think Yes, as I can see a few compatible strings in dts that don't
exist anywhere else.

My idea here is to add "amlogic,meson-t7-uart" for future use if ever
created, like if we find a bug in the future that is only relevant to
T7 soc.
But for now, fallback to s4 uart, as it seems to be the same controller.

>From Krzysztof said in the writing-bindings.rst, I am following the rules.

So, what's the path forward here?

Thanks
Lucas