linux-kernel - Re: [PATCH V5 1/5] dt-bindings: serial: meson: Drop legacy compatible.

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Date:   Mon, 10 Jan 2022 10:18:02 -0600
From:   Rob Herring <robh+dt@...nel.org>
To:     Yu Tu <yu.tu@...ogic.com>
Cc:     "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        "open list:ARM/Amlogic Meson..." <linux-amlogic@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        devicetree@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Neil Armstrong <narmstrong@...libre.com>,
        Kevin Hilman <khilman@...libre.com>,
        Jerome Brunet <jbrunet@...libre.com>,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>
Subject: Re: [PATCH V5 1/5] dt-bindings: serial: meson: Drop legacy compatible.

On Mon, Jan 10, 2022 at 4:42 AM Yu Tu <yu.tu@...ogic.com> wrote:
>
> Deprecated, don't use anymore because legacy amlogic,meson-gx-uart
> compatible. Don't differentiate between GXBB, GXL and G12A which
> have different revisions of the UART IP. So it's split into
> GXBB,GXL and G12A.

You are breaking compatibility. If your dts is updated to use the new
compatible, then a kernel without the change will not work anymore. It
worked before without understanding the changes you are making. It
should continue to. A compatible value like this would accomplish what
you want:

"amlogic,meson-gxbb-uart", "amlogic,meson-gx-uart", "amlogic,meson-ao-uart"

A new kernel will match on "amlogic,meson-gxbb-uart" or
"amlogic,meson-gx-uart" depending if the dtb is updated or not. An old
kernel will continue to match on "amlogic,meson-gx-uart".

If you are going to go breaking things, the power domain distinction
in the compatible is odd...

Rob