RE: [PATCH v5 2/3] dt-bindings: pci-imx6: Add external reference clock mode support

[Hongxing Zhu]

> -----Original Message-----
> From: Rob Herring <robh@xxxxxxxxxx>
> Sent: 2025年9月22日 23:51
> To: Hongxing Zhu <hongxing.zhu@xxxxxxx>
> Cc: Frank Li <frank.li@xxxxxxx>; l.stach@xxxxxxxxxxxxxx; lpieralisi@xxxxxxxxxx;
> kwilczynski@xxxxxxxxxx; mani@xxxxxxxxxx; krzk+dt@xxxxxxxxxx;
> conor+dt@xxxxxxxxxx; bhelgaas@xxxxxxxxxx; shawnguo@xxxxxxxxxx;
> s.hauer@xxxxxxxxxxxxxx; kernel@xxxxxxxxxxxxxx; festevam@xxxxxxxxx;
> linux-pci@xxxxxxxxxxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx;
> devicetree@xxxxxxxxxxxxxxx; imx@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH v5 2/3] dt-bindings: pci-imx6: Add external reference clock
> mode support
> 
> On Mon, Sep 15, 2025 at 11:53:47AM +0800, Richard Zhu wrote:
> > On i.MX, PCIe has two reference clock inputs: one from the internal
> > PLL and one from an external clock source. Only one needs to be used,
> > depending on the board design. Add the external reference clock source
> > for reference clock.
> >
> > Signed-off-by: Richard Zhu <hongxing.zhu@xxxxxxx>
> > Reviewed-by: Frank Li <Frank.Li@xxxxxxx>
> > ---
> >  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..6be45abe6e52 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 has two reference clock
> > +                    inputs, internal system PLL and external clock
> > +                    source. Only one needs to be used.
> > +                  enum: [ref, extref]
> 
> This seems wrong to me. There's still only 1 ref input to the PCIe block. If you
> had 10 possible choices for the ref clock source, would you add 10 clock names
> here? No!
> 
> Can't you detect what the parent clock is for the 'ref' clock? and configure the
> GPR register appropriately. Or that mux should be modeled as a clock provider.
Hi Rob:
Thanks for your concerns.
Per to the discussion about clock source.
https://lore.kernel.org/imx/aGKm41I%2FFsrWN8jN@lizhi-Precision-Tower-5810/
There are two clock sources on i.MX95 PCIe.

Best Regards
Richard Zhu
> 
> Rob