linux-kernel - Re: [PATCH 2/3] dt-bindings: usb: mtk-xhci: Allow middle optional clocks to be missing

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Date:   Sun, 19 Jun 2022 14:05:30 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Chunfeng Yun <chunfeng.yun@...iatek.com>,
        Nícolas F. R. A. Prado 
        <nfraprado@...labora.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Matthias Brugger <matthias.bgg@...il.com>
Cc:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>, kernel@...labora.com,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-mediatek@...ts.infradead.org, linux-usb@...r.kernel.org
Subject: Re: [PATCH 2/3] dt-bindings: usb: mtk-xhci: Allow middle optional
 clocks to be missing

On 19/06/2022 09:46, Chunfeng Yun wrote:
> On Fri, 2022-06-17 at 18:25 -0700, Krzysztof Kozlowski wrote:
>> On 17/06/2022 15:29, Nícolas F. R. A. Prado wrote:
>>> The current clock list in the binding doesn't allow for one of the
>>> optional clocks to be missing and a subsequent clock to be present.
>>> An
>>> example where this is an issue is in mt8192.dtsi, which has
>>> "sys_ck",
>>> "ref_ck", "xhci_ck" and would cause dtbs_check warnings.
>>>
>>> Change the clock list in a way that allows the middle optional
>>> clocks to
>>> be missing, while still guaranteeing a fixed order. The "ref_ck" is
>>> kept
>>> as a const even though it is optional for simplicity, since it is
>>> present in all current dts files.
>>>
>>> Signed-off-by: Nícolas F. R. A. Prado <nfraprado@...labora.com>
>>> ---
>>>
>>>  .../devicetree/bindings/usb/mediatek,mtk-xhci.yaml       | 9
>>> +++++++--
>>>  1 file changed, 7 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/Documentation/devicetree/bindings/usb/mediatek,mtk-
>>> xhci.yaml b/Documentation/devicetree/bindings/usb/mediatek,mtk-
>>> xhci.yaml
>>> index 63cbc2b62d18..99a1b233ec90 100644
>>> --- a/Documentation/devicetree/bindings/usb/mediatek,mtk-xhci.yaml
>>> +++ b/Documentation/devicetree/bindings/usb/mediatek,mtk-xhci.yaml
>>> @@ -80,8 +80,13 @@ properties:
>>>      items:
>>>        - const: sys_ck  # required, the following ones are optional
>>>        - const: ref_ck
>>> -      - const: mcu_ck
>>> -      - const: dma_ck
>>> +      - enum:
>>> +          - mcu_ck
>>> +          - dma_ck
>>> +          - xhci_ck
>>> +      - enum:
>>> +          - dma_ck
>>> +          - xhci_ck
>>>        - const: xhci_ck
>>
>> You allow now almost any order here, including incorrect like
>> sys,ref,xhci,xhci,xhci.
>>
>> The order of clocks has to be fixed and we cannot allow flexibility.
>> Are
>> you sure that these clocks are actually optional (not wired to the
>> device)?
> In fact, these optional clocks are fixed, due to no gates are provided,
> SW can't control them by CCF;
> In this case, I usually use a fixed clock, or ignore it.

But in some versions these clocks are controllable or not?

Best regards,
Krzysztof