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

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Date: Fri, 15 Dec 2023 11:53:28 +0100
From: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To: Jie Luo <quic_luoj@...cinc.com>, 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 15/12/2023 11:40, Jie Luo wrote:
> 
> 
> 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.

All clocks are some hardware pin connections.

Best regards,
Krzysztof