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

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Message-ID: <a3217699-7b23-35e6-84b2-fe9e52158481@linaro.org>
Date:   Sat, 18 Feb 2023 15:55:25 +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 18/02/2023 12:17, Conor Dooley wrote:
> Hey Krzysztof,
> 
> On Sat, Feb 18, 2023 at 11:20:30AM +0100, Krzysztof Kozlowski wrote:
>> 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).
> 
> You skipped this part which was what I was trying to ask you about.

Yeah, I skipped a lot because there was one big thread with a question:
what do you think? Sorry, I will not dig 8 emails thread to figure out
which question is to me and which is not...

> Do you know how to convey this situation, or is it even possible to
> express those rules?

oneOf:
 - clock-names:
     minItems: 3
     items:
       - a
       - b
       - c
       - d
 - clock-names:
     items:
       - a
       - b
       - d

or maybe:
 - clock-names:
     minItems: 3
     items:
       - a
       - b
       - enum: [c, d]
       - d


> 
>>>> 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...
> 
> I don't understand what you mean by this, sorry.

You said to a letter addressed to me "whether the hardware allows for
...". Why would you ask me about hardware I know nothing about? That was
my question - I am asking - whether hardware allows it or not. Then
write bindings depending on that.

Best regards,
Krzysztof