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

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Date:   Sat, 18 Feb 2023 11:20:30 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Conor Dooley <conor@...nel.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 17/02/2023 17:27, Conor Dooley wrote:
> 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.

Whether hardware allows - not a question to me. BTW, this is rather
question coming from me...

Best regards,
Krzysztof