linux-kernel - Re: [PATCH v3 07/11] dt-bindings: clock: Add StarFive JH7110 system clock and reset generator

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Date:   Fri, 17 Feb 2023 16:27:34 +0000
From:   Conor Dooley <conor@...nel.org>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc:     Conor Dooley <conor.dooley@...rochip.com>,
        Hal Feng <hal.feng@...rfivetech.com>,
        linux-riscv@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-clk@...r.kernel.org, Palmer Dabbelt <palmer@...belt.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Stephen Boyd <sboyd@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Emil Renner Berthing <emil.renner.berthing@...onical.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 07/11] dt-bindings: clock: Add StarFive JH7110 system
 clock and reset generator

On Fri, Feb 17, 2023 at 04:47:48PM +0100, Krzysztof Kozlowski wrote:
> On 17/02/2023 14:32, Conor Dooley wrote:
> >>>> Yes, it is.
> >>>
> >>> Which would then make GMAC1 RGMII RX optional, rather than required?
> >>
> >> If thinking in this way, I must say yes, it is optional. But actually
> >> GMAC1 RGMII RX feeds gmac1_rx by default. 
> >> For a mux, it usually works if you populate only one input to it.
> >> Does it mean all the other inputs are optional? And how can we define
> >> which input is required?
> > 
> > I'm not sure, that is a question for Krzysztof and/or Rob.
> 
> That's a long thread, please summarize what you ask. Otherwise I have no
> clue what is the question.

Sorry. I tried to preserve the context of the conversation the last time
I cropped it so that things would be contained on one email.

For me at least, I am wondering how you convey that out of a list of
clock inputs (for example a, b, c, d) that two of the clocks are inputs
to a mux and it is only required to provide one of the two (say b & c).

> Does the mux works correctly if clock input is not connected? I mean,
> are you now talking about real hardware or some simplification from SW
> point of view?

I'm coming at this from an angle of "is a StarFive customer going to show
up with a devicetree containing dummy fixed-clocks to satisfy dtbs_check
because they opted to only populate one input to the mux".
I don't really care about implications for the driver, just about
whether the hardware allows for inputs to the mux to be left
un-populated.

Cheers,
Conor.


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