linux-kernel - Re: [PATCH v3 05/10] dt-bindings: clock: ipq9574: Rename NSS CC source clocks to drop rate

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Message-ID: <830f3989-d1ac-4b7c-8888-397452fe0abe@quicinc.com>
Date: Fri, 18 Jul 2025 23:51:34 +0800
From: Luo Jie <quic_luoj@...cinc.com>
To: Konrad Dybcio <konrad.dybcio@....qualcomm.com>,
        Rob Herring
	<robh@...nel.org>
CC: Georgi Djakov <djakov@...nel.org>,
        Krzysztof Kozlowski
	<krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Bjorn Andersson
	<andersson@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        "Stephen
 Boyd" <sboyd@...nel.org>,
        Anusha Rao <quic_anusha@...cinc.com>,
        Konrad Dybcio
	<konradybcio@...nel.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        "Richard
 Cochran" <richardcochran@...il.com>,
        Catalin Marinas
	<catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, <linux-arm-msm@...r.kernel.org>,
        <linux-pm@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-clk@...r.kernel.org>,
        <netdev@...r.kernel.org>, <linux-arm-kernel@...ts.infradead.org>,
        <quic_kkumarcs@...cinc.com>, <quic_linchen@...cinc.com>,
        <quic_leiwei@...cinc.com>, <quic_pavir@...cinc.com>,
        <quic_suruchia@...cinc.com>
Subject: Re: [PATCH v3 05/10] dt-bindings: clock: ipq9574: Rename NSS CC
 source clocks to drop rate



On 7/18/2025 5:28 PM, Konrad Dybcio wrote:
> On 7/18/25 11:12 AM, Luo Jie wrote:
>>
>>
>> On 7/11/2025 8:15 PM, Konrad Dybcio wrote:
>>> On 7/11/25 12:54 AM, Rob Herring wrote:
>>>> On Thu, Jul 10, 2025 at 08:28:13PM +0800, Luo Jie wrote:
>>>>> Drop the clock rate suffix from the NSS Clock Controller clock names for
>>>>> PPE and NSS clocks. A generic name allows for easier extension of support
>>>>> to additional SoCs that utilize same hardware design.
>>>>
>>>> This is an ABI change. You must state that here and provide a reason the
>>>> change is okay (assuming it is). Otherwise, you are stuck with the name
>>>> even if not optimal.
>>>
>>> The reason here seems to be simplifying the YAML.. which is not a good
>>> reason really..
>>>
>>> I would instead suggest keeping the clocks list as-is for ipq9574 (this
>>> existing case), whereas improving it for any new additions
>>>
>>> Konrad
>>
>> Thanks Rob and Konrad for the comments.
>>
>> "nss_1200" and "nss" refer to the same clock pin on different SoC.
>> As per Krzystof's previous comment on V2, including the frequency
>> as a suffix in the clock name is not required, since only the
>> frequencies vary across different IPQ SoCs, while the source clock
>> pins for 'PPE' and 'NSS' clocks are the same. Hence this ABI change
>> was deemed necessary.
>>
>> By removing the frequency suffix, the device tree bindings becomes
>> more flexible and easier to extend for supporting new hardware
>> variants in the future.
>>
>> Impact due to this ABI change: The NSS clock controller node is only
>> enabled for the IPQ9574 DTS. In this patch series, the corresponding
>> DTS changes for IPQ9574 are also included to align with this ABI
>> change.
> 
> The point of an ABI is to keep exposing the same interface without
> any change requirements, i.e. if a customer ships the DT from
> torvalds/master in firmware and is not willing to update it, they
> can no longer update the kernel without a workaround.
> 
>> Please let me know if further clarification or adjustments are needed.
> 
> What we're asking for is that you don't alter the name on the
> existing platform, but use a no-suffix version for the ones you
> introduce going forward
> 
> i.e. (pseudo-YAML)
> 
> if:
>    properties:
>      compatible:
>        - const: qcom,ipq9574-nsscc
> then:
>    properties:
>      clock-names:
>        items:
>          - clockname_1200
> else:
>    properties:
>      clock-names:
>        items:
>          - clockname # no suffix
> 
> Konrad

We had adopted this proposal in version 2 previously, but as noted in
the discussion linked below, Krzysztof had suggested to avoid using the
clock rate in the clock names when defining the constraints for them.
However I do agree that we should keep the interface for IPQ9574
unchanged and instead use a generic clock name to support the newer
SoCs.

https://lore.kernel.org/all/20250701-optimistic-esoteric-swallow-d93fc6@krzk-bin/

Request Krzysztof to provide his comments as well, on whether we can
follow your suggested approach to avoid breaking ABI for IPQ9574.