linux-kernel - RE: [PATCH v8 2/3] dt-bindings: PCI: pci-imx6: Add external reference clock input

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Message-ID:
 <AS8PR04MB8833DEEA9CB4CE4968B2B5F18CFCA@AS8PR04MB8833.eurprd04.prod.outlook.com>
Date: Mon, 27 Oct 2025 06:36:32 +0000
From: Hongxing Zhu <hongxing.zhu@....com>
To: Conor Dooley <conor@...nel.org>
CC: "robh@...nel.org" <robh@...nel.org>, "krzk+dt@...nel.org"
	<krzk+dt@...nel.org>, "conor+dt@...nel.org" <conor+dt@...nel.org>,
	"bhelgaas@...gle.com" <bhelgaas@...gle.com>, Frank Li <frank.li@....com>,
	"l.stach@...gutronix.de" <l.stach@...gutronix.de>, "lpieralisi@...nel.org"
	<lpieralisi@...nel.org>, "kwilczynski@...nel.org" <kwilczynski@...nel.org>,
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	<shawnguo@...nel.org>, "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
	"kernel@...gutronix.de" <kernel@...gutronix.de>, "festevam@...il.com"
	<festevam@...il.com>, "linux-pci@...r.kernel.org"
	<linux-pci@...r.kernel.org>, "linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>, "devicetree@...r.kernel.org"
	<devicetree@...r.kernel.org>, "imx@...ts.linux.dev" <imx@...ts.linux.dev>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v8 2/3] dt-bindings: PCI: pci-imx6: Add external reference
 clock input

> -----Original Message-----
> From: Conor Dooley <conor@...nel.org>
> Sent: 2025年10月25日 1:07
> To: Hongxing Zhu <hongxing.zhu@....com>
> Cc: robh@...nel.org; krzk+dt@...nel.org; conor+dt@...nel.org;
> bhelgaas@...gle.com; Frank Li <frank.li@....com>; l.stach@...gutronix.de;
> lpieralisi@...nel.org; kwilczynski@...nel.org; mani@...nel.org;
> shawnguo@...nel.org; s.hauer@...gutronix.de; kernel@...gutronix.de;
> festevam@...il.com; linux-pci@...r.kernel.org;
> linux-arm-kernel@...ts.infradead.org; devicetree@...r.kernel.org;
> imx@...ts.linux.dev; linux-kernel@...r.kernel.org
> Subject: Re: [PATCH v8 2/3] dt-bindings: PCI: pci-imx6: Add external reference
> clock input
> 
> On Fri, Oct 24, 2025 at 10:40:12AM +0800, Richard Zhu wrote:
> > i.MX95 PCIes have two reference clock inputs: one from internal PLL,
> > the other from off chip crystal oscillator. The "extref" clock refers
> > to a reference clock from an external crystal oscillator.
> >
> > Add external reference clock input for i.MX95 PCIes.
> >
> > Signed-off-by: Richard Zhu <hongxing.zhu@....com>
> > Reviewed-by: Frank Li <Frank.Li@....com>
> > ---
> >  Documentation/devicetree/bindings/pci/fsl,imx6q-pcie.yaml | 3 +++
> >  1 file changed, 3 insertions(+)
> >
> > diff --git a/Documentation/devicetree/bindings/pci/fsl,imx6q-pcie.yaml
> > b/Documentation/devicetree/bindings/pci/fsl,imx6q-pcie.yaml
> > index ca5f2970f217c..b4c40d0573dce 100644
> > --- a/Documentation/devicetree/bindings/pci/fsl,imx6q-pcie.yaml
> > +++ b/Documentation/devicetree/bindings/pci/fsl,imx6q-pcie.yaml
> > @@ -212,14 +212,17 @@ allOf:
> >      then:
> >        properties:
> >          clocks:
> > +          minItems: 4
> >            maxItems: 5
> >          clock-names:
> > +          minItems: 4
> >            items:
> >              - const: pcie
> 
> 1
> 
> >              - const: pcie_bus
> 
> 2
> 
> >              - const: pcie_phy
> 
> 3
> 
> >              - const: pcie_aux
> 
> 4
> 
> >              - const: ref
> 
> 5
> 
> > +            - const: extref  # Optional
> 
> 6
> 
> There are 6 clocks here, but clocks and clock-names in this binding do not
> permit 6:
> |  clocks:
> |    minItems: 3
> |    items:
> |      - description: PCIe bridge clock.
> |      - description: PCIe bus clock.
> |      - description: PCIe PHY clock.
> |      - description: Additional required clock entry for imx6sx-pcie,
> |           imx6sx-pcie-ep, imx8mq-pcie, imx8mq-pcie-ep.
> |      - description: PCIe reference clock.
> |
> |  clock-names:
> |    minItems: 3
> |    maxItems: 5
> 
> AFAICT, what this patch actually did is make "ref" an optional clock, but the
> claim in the patch is that extref is optional. With this patch applied, you can
> have a) no reference clocks or b) only "ref". "extref"
> is never allowed. 
Hi Conor:
Thanks for your review comments.
Just same to "extref", the "ref" should be marked as optional clock too.

> 
> Is it supposed to be possible to have "ref" and "extref"?
> Or "extref" without "ref"?
> Neither "ref" or "extref"?
"ref" and "extref" have an exclusive relationship of choosing one of the two,
 and they cannot all exist simultaneously.

> I don't know the answer to that question because you're doing things that
> are contradictory in your patch and the commit message isn't clear.
> 
Sorry for causing you confusion.


Best Regards
Richard Zhu

> I don't see how this can have been successfully tested.
> 
> pw-bot: changes-requested