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

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Date:   Wed, 22 Jun 2022 09:57:12 +0800
From:   Chunfeng Yun <chunfeng.yun@...iatek.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        "Nícolas F. R. A. Prado" <nfraprado@...labora.com>,
        Wenbin Mei <wenbin.mei@...iatek.com>
CC:     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 Tue, 2022-06-21 at 09:14 +0200, Krzysztof Kozlowski wrote:
> 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 right for me.

> 
> > 
> > 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.

I discussed it with Wenbin, MMC seems a little different with USB,

Hi Wenbin,

   Please give some comments about MMC, thanks

> > 
> > Thanks,
> > Nícolas
> > 
> > [1] 
> > https://lore.kernel.org/all/20220617230114.2438875-1-nfraprado@collabora.com
> 
> 
> Best regards,
> Krzysztof