linux-kernel - Re: [PATCH v5 02/10] dt-bindings: phy: qcom,qmp-usb: Add Glymur USB UNI PHY compatible

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Message-ID: <b2b68430-5127-5eca-6bd8-4af31eb9fbed@oss.qualcomm.com>
Date: Thu, 16 Oct 2025 17:15:48 -0700
From: Wesley Cheng <wesley.cheng@....qualcomm.com>
To: Krzysztof Kozlowski <krzk@...nel.org>, krzk+dt@...nel.org,
        conor+dt@...nel.org, konrad.dybcio@....qualcomm.com,
        dmitry.baryshkov@....qualcomm.com, kishon@...nel.org, vkoul@...nel.org,
        gregkh@...uxfoundation.org, robh@...nel.org
Cc: linux-arm-msm@...r.kernel.org, linux-phy@...ts.infradead.org,
        linux-usb@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 02/10] dt-bindings: phy: qcom,qmp-usb: Add Glymur USB
 UNI PHY compatible



On 10/13/2025 9:36 PM, Krzysztof Kozlowski wrote:
> On 14/10/2025 03:16, Wesley Cheng wrote:
>>>>
>>>>>>> +          maxItems: 5
>>>>>>> +        clock-names:
>>>>>>> +          items:
>>>>>>> +            - const: aux
>>>>>>> +            - const: clkref
>>>>>>> +            - const: ref
>>>>>>
>>>>>> What is the difference between these two? Which block INPUTs
>>>>>> (important!) they represent?
>>>>>>
>>>>>
>>>>> clkref is the TCSR reference clock switch, and the ref is the actual CXO
>>>>> handle.
>>>
>>>
>>> Then this should be named somehow differently. CXO is clock. Reference
>>> clock is clock... To me it feels like you are describing the same clock,
>>> just missing some gate in TCSR. But in case these are not the same
>>> clocks, you need to name it accurately.
>>>
>>
>> Technically its all handling the same clock branch (CXO), we have the
>> TCSR clkref register that allows us to gate the CXO to the USB PHY, as
> 
> 
> Ah, exactly. Then clkref is not a clock. You need rather proper clock
> hierarchy.
> 
>> CXO is shared across several HW blocks, so it allows us to properly
>> powerdown the PHY even though other clients are voting for CXO on.  Then
>> we obviously have to remove our vote to the overall CXO, so that it can
>> potentially be shutdown.
>>
>> Maybe we can rename it to "clkref" for the CXO handle and
>> "clkref_switch" for the TCSRCC handle?
> 
> Naming is better, but it is still not correct. This is not independent
> clock signal. It is the same clock.
> 

Hmmm... I guess that's why I kept the same clkref tag, to denote that 
its the same clock, but one is a switch/gate for it.  Would you happen 
to have any suggestions you might have that makes it clearer for 
everyone to understand?

Thanks
Wesley Cheng