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

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Date:   Mon, 20 Jun 2022 14:59:58 +0800
From:   Chunfeng Yun <chunfeng.yun@...iatek.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        "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 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).

> 
> Best regards,
> Krzysztof