netdev - Re: [PATCH v2 5/5] dt-bindings: net: ipq4019-mdio: Document ipq5332 platform

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Date: Fri, 15 Dec 2023 18:40:54 +0800
From: Jie Luo <quic_luoj@...cinc.com>
To: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Conor Dooley
	<conor@...nel.org>
CC: <agross@...nel.org>, <andersson@...nel.org>, <konrad.dybcio@...aro.org>,
        <davem@...emloft.net>, <edumazet@...gle.com>, <kuba@...nel.org>,
        <pabeni@...hat.com>, <robh+dt@...nel.org>,
        <krzysztof.kozlowski+dt@...aro.org>, <conor+dt@...nel.org>,
        <andrew@...n.ch>, <hkallweit1@...il.com>, <linux@...linux.org.uk>,
        <robert.marko@...tura.hr>, <linux-arm-msm@...r.kernel.org>,
        <netdev@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <quic_srichara@...cinc.com>
Subject: Re: [PATCH v2 5/5] dt-bindings: net: ipq4019-mdio: Document ipq5332
 platform



On 12/15/2023 6:37 PM, Krzysztof Kozlowski wrote:
> On 15/12/2023 11:33, Jie Luo wrote:
>>>>>>>>>> +  cmn-reference-clock:
>>>>>>>>>> +    oneOf:
>>>>>>>>>> +      - items:
>>>>>>>>>> +          - enum:
>>>>>>>>>> +              - 0   # CMN PLL reference internal 48MHZ
>>>>>>>>>> +              - 1   # CMN PLL reference external 25MHZ
>>>>>>>>>> +              - 2   # CMN PLL reference external 31250KHZ
>>>>>>>>>> +              - 3   # CMN PLL reference external 40MHZ
>>>>>>>>>> +              - 4   # CMN PLL reference external 48MHZ
>>>>>>>>>> +              - 5   # CMN PLL reference external 50MHZ
>>>>>>>>>> +              - 6   # CMN PLL reference internal 96MHZ
>>>>>>>>>
>>>>>>>>> Why is this not represented by an element of the clocks property?
>>>>>>>>
>>>>>>>> This property is for the reference clock source selection of CMN PLL,
>>>>>>>> CMN PLL generates the different clock rates for the different Ethernet
>>>>>>>> blocks, this CMN PLL configuration is not located in the GCC, so the
>>>>>>>> clock framework can't be used, which is the general hardware register
>>>>>>>> instead of RCG register for GCC.
>>>>>>>
>>>>>>> I don't see how the clock being provided by the "GCC" (whatever that is)
>>>>>>> or by some other clock controller or fixed clock makes a difference.
>>>>>>> Why can't the other clock provider be represented in the devicetree?
>>>>>>>
>>>>>>
>>>>>> cmn-reference-clock is for selecting the reference clock source for the
>>>>>> whole Ethernet block, which is just the standalone configure register.
>>>>>
>>>>> Sure, you are aware though that all clocks are just configure registers?
>>>>>
>>>>> Which clocks are these mentioned in the property? From where do they come?
>>>>>
>>>>> Anyway, property is in existing form is not correct - this is not a
>>>>> generic property.
>>>>>
>>>>
>>>> This property cmn-reference-clock is just the hardware register
>>>> configuration, since the different IPQ platform needs to select
>>>> the different reference clock source for the CMN PLL block that
>>>> provides the various clock outputs to the all kinds of Ethernet
>>>> devices, which is not from GCC provider.
>>>
>>> AGAIN: where do the clocks come from? Which device generates them?
>>
>> Oh, OK, the reference clock is from wifi that provides 48MHZ to
>> Ethernet block.
> 
> Then WiFi should be providing you the clock and this device should be
> clock consumer, right?

Yes, wifi provides 48MHz clock to CMM PLL block, there is no GCC
for this 48MHZ clock output, it is the hardware PIN connection.
> 
> 
> 
> Best regards,
> Krzysztof
>