netdev - Re: RFC: Advice on adding support for Qualcomm IPQ9574 SoC Ethernet

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Message-ID: <6e764e04-acbd-4973-af59-f58203a556dd@quicinc.com>
Date: Fri, 25 Oct 2024 18:33:41 +0530
From: Kiran Kumar C.S.K <quic_kkumarcs@...cinc.com>
To: Andrew Lunn <andrew@...n.ch>
CC: "Russell King (Oracle)" <linux@...linux.org.uk>, <netdev@...r.kernel.org>,
        Andy Gross <agross@...nel.org>, Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        "David S. Miller"
	<davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski
	<kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, Rob Herring
	<robh+dt@...nel.org>,
        Krzysztof Kozlowski
	<krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Jacob Keller
	<jacob.e.keller@...el.com>,
        Bhupesh Sharma <bhupesh.sharma@...aro.org>,
        <linux-arm-msm@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <vsmuthu@....qualcomm.com>,
        <arastogi@....qualcomm.com>, <linchen@....qualcomm.com>,
        <john@...ozen.org>, Luo Jie <quic_luoj@...cinc.com>,
        Pavithra R <quic_pavir@...cinc.com>,
        "Suruchi Agarwal (QUIC)" <quic_suruchia@...cinc.com>,
        "Lei Wei (QUIC)"
	<quic_leiwei@...cinc.com>
Subject: Re: RFC: Advice on adding support for Qualcomm IPQ9574 SoC Ethernet



On 10/24/2024 7:57 PM, Andrew Lunn wrote:
>>> I'm just wondering if you have circular dependencies at runtime?
>>>
>>> Where you will need to be careful is probe time vs runtime. Since you
>>> have circular phandles you need to first create all the clock
>>> providers, and only then start the clock consumers. Otherwise you
>>> might get into an endless EPROBE_DEFER loop.
>>>
>>
>> The Rx/Tx clocks sourced from the SERDES are registered as provider
>> clocks by the UNIPHY/PCS driver during probe time. There is no runtime
>> operation needed for these clocks after this.
> 
> So they are always ticking. You cannot turn them on/off? It is nice to
> model them a fixed-clocks, since it describes the architecture, but i
> have to question if it is worth the effort.
> 

Yes, we cannot turn them off. However the rates of these clocks from
SERDES to NSSCC, is not fixed. It will be either 312.5Mhz or 125Mhz,
depending on the whether the SERDES mode is USXGMII or SGMII respectively.

> 	Andrew