linux-kernel - Re: [PATCH v3 1/2] dt-binding: pci-imx6: Add external reference clock mode support

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Message-ID: <6ojwsgzi4rrn7zoiktiutdjgaly4uhbe7xc35lafyxgl5yacwv@oajobetnqsps>
Date: Mon, 23 Jun 2025 08:49:25 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Frank Li <Frank.li@....com>
Cc: Hongxing Zhu <hongxing.zhu@....com>, 
	"l.stach@...gutronix.de" <l.stach@...gutronix.de>, "lpieralisi@...nel.org" <lpieralisi@...nel.org>, 
	"kwilczynski@...nel.org" <kwilczynski@...nel.org>, "mani@...nel.org" <mani@...nel.org>, 
	"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>, 
	"shawnguo@...nel.org" <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 v3 1/2] dt-binding: pci-imx6: Add external reference
 clock mode support

On Fri, Jun 20, 2025 at 10:40:52AM -0400, Frank Li wrote:
> On Fri, Jun 20, 2025 at 03:08:16PM +0200, Krzysztof Kozlowski wrote:
> > On 20/06/2025 10:26, Hongxing Zhu wrote:
> > >> -----Original Message-----
> > >> From: Krzysztof Kozlowski <krzk@...nel.org>
> > >> Sent: 2025年6月20日 15:53
> > >> To: Hongxing Zhu <hongxing.zhu@....com>
> > >> Cc: Frank Li <frank.li@....com>; l.stach@...gutronix.de;
> > >> lpieralisi@...nel.org; kwilczynski@...nel.org; mani@...nel.org;
> > >> robh@...nel.org; krzk+dt@...nel.org; conor+dt@...nel.org;
> > >> bhelgaas@...gle.com; 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 v3 1/2] dt-binding: pci-imx6: Add external reference clock
> > >> mode support
> > >>
> > >> On Fri, Jun 20, 2025 at 11:13:49AM GMT, Richard Zhu wrote:
> > >>> On i.MX, the PCIe reference clock might come from either internal
> > >>> system PLL or external clock source.
> > >>> Add the external reference clock source for reference clock.
> > >>>
> > >>> Signed-off-by: Richard Zhu <hongxing.zhu@....com>
> > >>> Reviewed-by: Frank Li <Frank.Li@....com>
> > >>> ---
> > >>>  Documentation/devicetree/bindings/pci/fsl,imx6q-pcie.yaml | 7 ++++++-
> > >>>  1 file changed, 6 insertions(+), 1 deletion(-)
> > >>>
> > >>> diff --git a/Documentation/devicetree/bindings/pci/fsl,imx6q-pcie.yaml
> > >>> b/Documentation/devicetree/bindings/pci/fsl,imx6q-pcie.yaml
> > >>> index ca5f2970f217..c472a5daae6e 100644
> > >>> --- a/Documentation/devicetree/bindings/pci/fsl,imx6q-pcie.yaml
> > >>> +++ b/Documentation/devicetree/bindings/pci/fsl,imx6q-pcie.yaml
> > >>> @@ -219,7 +219,12 @@ allOf:
> > >>>              - const: pcie_bus
> > >>>              - const: pcie_phy
> > >>>              - const: pcie_aux
> > >>> -            - const: ref
> > >>> +            - description: PCIe reference clock.
> > >>> +              oneOf:
> > >>> +                - description: The controller might be configured
> > >> clocking
> > >>> +                    coming in from either an internal system PLL or
> > >> an
> > >>> +                    external clock source.
> > >>> +                  enum: [ref, gio]
> > >>
> > >> Internal like within PCIe or coming from other SoC block? What does "gio"
> > >> mean?
> > > Internal means that the PCIe reference clock is coming from other
> > >  internal SoC block, such as system PLL. "gio" is on behalf that the
> > > reference clock comes form external crystal oscillator.
> >
> > Then what does "ref" mean, if gio is the clock supplied externally?
> 
> In snps,dw-pcie-common.yaml
> 
> 	- description:
>             Generic reference clock. In case if there are several
>             interfaces fed up with a common clock source it's advisable to
>             define it with this name (for instance pipe, core and aux can
>             be connected to a single source of the periodic signal).
>           const: ref
> 
>         - description: See native 'ref' clock for details.
>           enum: [ gio ]

... ok, but the rest of description is saying: don't use it.

Best regards,
Krzysztof