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From:   Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Date:   Tue, 30 May 2023 21:55:16 +0200
Message-ID: <CAFBinCCZcT=7BZsgXDjzbcqAZpEkKYZRBDRwDX1poWZHa9Hxdg@mail.gmail.com>
Subject: Re: [PATCH v15 5/6] dt-bindings: clock: meson: add A1 Peripherals
 clock controller bindings
To:     Dmitry Rokosov <ddrokosov@sberdevices.ru>
Cc:     Conor Dooley <conor.dooley@microchip.com>, jbrunet@baylibre.com,
        krzysztof.kozlowski+dt@linaro.org, neil.armstrong@linaro.org,
        mturquette@baylibre.com, sboyd@kernel.org, robh+dt@kernel.org,
        khilman@baylibre.com, jian.hu@amlogic.com, kernel@sberdevices.ru,
        rockosov@gmail.com, linux-amlogic@lists.infradead.org,
        linux-clk@vger.kernel.org, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org
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Hi,

On Tue, May 30, 2023 at 6:03=E2=80=AFPM Dmitry Rokosov <ddrokosov@sberdevic=
es.ru> wrote:
[...]
> > If I am understanding correctly, this series implements the child
> > controller and a parent, which is unimplemented, provides the child wit=
h
> > sys_pll_div16.
> > The thing I am missing is whether the child controller has some outputs
> > that depend on this sys_pll_div16 input & whether those are documented
> > in this series. Regardless, you should be able to add more output clock=
s
> > without compatibility issues.
Conor, the short answer is yes, the "gen_sel" mux (see patch 6/6 from
this series, which is then part of a clock tree that's an output of
the peripheral clock controller) uses sys_pll_div16 as input.
Dmitry goes into more details below.

[...]
> As for new input clock connections, such as the cpu_clock
> (sys_pll_div16), these are handled by clock muxing abstraction, allowing
> CCF to find the clock object by fw.name and returning -ENOENT if the
> connection is missing without breaking any CCF flow. It happens in the
> kernel function clk_core_fill_parent_index()
> https://elixir.bootlin.com/linux/latest/source/drivers/clk/clk.c#L424
> Despite not having the connection for the new input in the old Device
> Tree version, this will not break kernel boot flow and workflow, and the
> new clock object just would not be utilized.
>
> Based on the presented arguments, I fully agree with Jerome's position.
> We can add new connections and objects in new driver versions, but their
> removal is prohibited.
>
> If it's alright with you, I would prefer to keep the Peripherals and PLL
> clock driver and their bindings as they are, and continue with the CPU
> and Audio clock controllers in a separate patch series. Would that be
> feasible for you?
To me this sounds good!


Best regards,
Martin