linux-kernel - Re: [PATCH v15 5/6] dt-bindings: clock: meson: add A1 Peripherals clock controller bindings

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Date:   Tue, 30 May 2023 21:55:16 +0200
From:   Martin Blumenstingl <martin.blumenstingl@...glemail.com>
To:     Dmitry Rokosov <ddrokosov@...rdevices.ru>
Cc:     Conor Dooley <conor.dooley@...rochip.com>, jbrunet@...libre.com,
        krzysztof.kozlowski+dt@...aro.org, neil.armstrong@...aro.org,
        mturquette@...libre.com, sboyd@...nel.org, robh+dt@...nel.org,
        khilman@...libre.com, jian.hu@...ogic.com, kernel@...rdevices.ru,
        rockosov@...il.com, linux-amlogic@...ts.infradead.org,
        linux-clk@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v15 5/6] dt-bindings: clock: meson: add A1 Peripherals
 clock controller bindings

Hi,

On Tue, May 30, 2023 at 6:03 PM Dmitry Rokosov <ddrokosov@...rdevices.ru> wrote:
[...]
> > If I am understanding correctly, this series implements the child
> > controller and a parent, which is unimplemented, provides the child with
> > 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 clocks
> > 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