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Date:   Wed, 21 Jun 2023 09:01:39 +0100
From:   Conor Dooley <conor.dooley@microchip.com>
To:     Lucas Tanure <tanure@linux.com>
CC:     Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>,
        Yixun Lan <dlan@gentoo.org>, Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Conor Dooley <conor+dt@kernel.org>,
        Neil Armstrong <neil.armstrong@linaro.org>,
        Jerome Brunet <jbrunet@baylibre.com>,
        Kevin Hilman <khilman@baylibre.com>, Nick <nick@khadas.com>,
        Artem <art@khadas.com>, <devicetree@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>,
        <linux-amlogic@lists.infradead.org>,
        <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v2 2/2] arm64: dts: meson-t7-a311d2-khadas-vim4: add
 initial device-tree
Message-ID: <20230621-barber-enjoyably-04806271daea@wendy>
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On Wed, Jun 21, 2023 at 08:37:02AM +0100, Lucas Tanure wrote:
> On Wed, Jun 21, 2023 at 7:02=E2=80=AFAM Krzysztof Kozlowski
> <krzysztof.kozlowski@linaro.org> wrote:
> >
> > On 21/06/2023 00:09, Yixun Lan wrote:
> > >> +            apb4: bus@fe000000 {
> > >> +                    compatible =3D "simple-bus";
> > >> +                    reg =3D <0x0 0xfe000000 0x0 0x480000>;
> > >> +                    #address-cells =3D <2>;
> > >> +                    #size-cells =3D <2>;
> > >> +                    ranges =3D <0x0 0x0 0x0 0xfe000000 0x0 0x480000=
>;
> > >> +
> > >> +                    uart_A: serial@78000 {
> > >> +                            compatible =3D "amlogic,meson-t7-uart",
> > >                                               ~~~~~~~~~~~~~~~~~
> > > if you introduce new compatible string, then at least you need to doc=
ument it
> > > so Documentation/devicetree/bindings/serial/amlogic,meson-uart.yaml n=
eed 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 str=
ucture length of
> > > meson_uart_dt_match[], but also relieve maintainer's review burden?
> >
> > https://elixir.bootlin.com/linux/v6.1-rc1/source/Documentation/devicetr=
ee/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?

No, you can't.

> I think Yes, as I can see a few compatible strings in dts that don't
> exist anywhere else.

Aye, but we do not want to propagate that. New stuff should not be
adding undocumented compatibles, and those that are undocumented should
be documented.

> 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.
>=20
> >From Krzysztof said in the writing-bindings.rst, I am following the rule=
s.
>=20
> So, what's the path forward here?

You are following the rules from the dts point of view, you just need a
3rd patch in which you document the pattern you have added here in
amlogic,meson-uart.yaml. It is probably something like:
+      - items:
+          - const: amlogic,meson-t7-uart
+          - const: amlogic,meson-s4-uart
But I have not tested that, I just wrote that in my mail client.

Cheers,
Conor.

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