Re: [PATCH 2/3] PCI: imx6: Use the external clock as REF_CLK when needed for i.MX8MQ

On Sun, Aug 02, 2026 at 11:49:27AM +0000, [email protected] wrote:
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [High] The patch breaks backward compatibility with existing i.MX8MQ device trees by changing the default reference clock source, causing PCIe initialization to fail.
> --
>
> --- Patch [2]: [PATCH 2/3] PCI: imx6: Use the external clock as REF_CLK when needed for i.MX8MQ ---
> commit 6f37370c304d3692e11e97087dc50e68e2389b9e
> Author: Rudi Heitbaum <[email protected]>
>
> PCI: imx6: Use the external clock as REF_CLK when needed for i.MX8MQ
>
> This commit updates the i.MX8MQ PCIe PHY initialization to conditionally
> select the external oscillator as the reference clock based on the
> enable_ext_refclk flag. It falls back to the internal PLL if an "extref"
> clock is not supplied.
>
> > diff --git a/drivers/pci/controller/dwc/pci-imx6.c b/drivers/pci/controller/dwc/pci-imx6.c
> > index 98e1db751132a..9e3b64fecb451 100644
> > --- a/drivers/pci/controller/dwc/pci-imx6.c
> > +++ b/drivers/pci/controller/dwc/pci-imx6.c
> > @@ -445,11 +445,16 @@ static int pcie_phy_write(struct imx_pcie *imx_pcie, int addr, u16 data)
> >
> >  static int imx8mq_pcie_init_phy(struct imx_pcie *imx_pcie)
> >  {
> > -	/* TODO: This code assumes external oscillator is being used */
> > +	bool ext = imx_pcie->enable_ext_refclk;
> > +
> > +	/*
> > +	 * Select the off-chip oscillator as REF_CLK when an "extref" clock is
> > +	 * supplied, otherwise fall back to the internal PLL.
> > +	 */
> >  	regmap_update_bits(imx_pcie->iomuxc_gpr,
> >  			   imx_pcie_grp_offset(imx_pcie),
> >  			   IMX8MQ_GPR_PCIE_REF_USE_PAD,
> > -			   IMX8MQ_GPR_PCIE_REF_USE_PAD);
> > +			   ext ? IMX8MQ_GPR_PCIE_REF_USE_PAD : 0);
>
> [Severity: High]
> Will this change break backward compatibility with existing i.MX8MQ device
> trees?

This is problem.  enable_ext_refclk is good direction to align imx95. but
need find way to avoid break backward compatibility.

Frank
>
> Looking at imx8mq_pcie_init_phy() in drivers/pci/controller/dwc/pci-imx6.c,
> if a legacy device tree does not provide a clock named "extref",
> imx_pcie->enable_ext_refclk evaluates to false.
>
> This causes the driver to clear IMX8MQ_GPR_PCIE_REF_USE_PAD and fall back to
> the internal PLL. On boards that previously relied on the unconditional
> external oscillator selection, this regression will cause PCIe initialization
> to fail.
>
> --
> Sashiko AI review · https://sashiko.dev/#/patchset/[email protected]?part=2