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

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Message-ID: <afae6179-3681-f5c6-4615-3228f16f1271@linaro.org>
Date:   Tue, 21 Jun 2022 09:14:50 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Nícolas F. R. A. Prado 
        <nfraprado@...labora.com>
Cc:     Chunfeng Yun <chunfeng.yun@...iatek.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        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 20/06/2022 17:50, Nícolas F. R. A. Prado wrote:
> On Mon, Jun 20, 2022 at 10:50:57AM +0200, Krzysztof Kozlowski wrote:
>> On 20/06/2022 08:59, Chunfeng Yun wrote:
>>> On Sun, 2022-06-19 at 14:05 +0200, Krzysztof Kozlowski wrote:
>>>> 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?
>>> Some SoCs are controllable, some ones are not (fixed clock).
>>
>> Thanks for confirming. Then I would prefer to make these clocks required
>> (not optional) and always provide them - via common clock framework or
>> fixed-clock.
> 
> Hi Krzysztof and Chunfeng,
> 
> thank you both for the feedback.
> 
> Since the solution I proposed in this patch is not acceptable I see two options:
> 1. Split the clocks in several if blocks matched by compatibles
> 2. Make the clocks required and use fixed-clock nodes for the missing clocks in
>    the DT
> 
> My understanding is that 1 is the desirable solution if the clock is really
> missing in some hardware variants, while 2 is desirable if all hardware variants
> really receive all the clocks, only that on some variants they're fixed and not
> controlable by SW.
> 
> From what I'm reading of this discussion it seems that the latter is the case
> here and thus we should go for 2. Is this correct?

This is how I understood it as well, so correct from my side.

> 
> Also Chunfeng, do you have information on whether the same is true for the MMC
> HW block? I recently submitted some changes to that binding [1] but I followed
> approach 1 there instead. However if all the clocks are present in the HW level
> there as well it would make more sense for me to change it to follow approach 2.
> 
> Thanks,
> Nícolas
> 
> [1] https://lore.kernel.org/all/20220617230114.2438875-1-nfraprado@collabora.com


Best regards,
Krzysztof