Re: [PATCH v5] PCI: imx6: Update MPLLB bandwidth to improve i.MX95 Gen3 PCIe stability

[Frank Li <Frank.li@oss.nxp.com>]

On Thu, Sep 10, 2026 at 12:46:43PM +0200, Manivannan Sadhasivam wrote:
> On Mon, Aug 03, 2026 at 11:43:19AM +0800, hongxing.zhu@oss.nxp.com wrote:
> > From: Richard Zhu <hongxing.zhu@nxp.com>
> >
> > We observed poor bandwidth margins during i.MX95 Gen3 PCIe tests with
> > the default MPLLB_BANDWIDTH value (120). The margins worsened across
> > voltage and temperature (VT) variations and different test matrices,
> > potentially causing link stability issues.
> >
> > Testing with MPLLB_BANDWIDTH value of 140 (0x8c) shows significant
> > improvement in bandwidth margins across all VT conditions and test
> > scenarios.
> >
> > Implement PHY register write helper function and configure:
> > - MPLLB_BW_OVRD_IN = 140 (0x8c) for improved bandwidth margin
> > - MPLLB_BW_OVRD_EN to enable the override
> >
> > This ensures robust PCIe Gen3 performance across all operating
> > conditions.
> >
> > Signed-off-by: Richard Zhu <hongxing.zhu@nxp.com>
> > Reviewed-by: Frank Li <Frank.Li@nxp.com>
> > ---
> > Changes in v5:
> > Update the commit log refer to Bjorn's suggestions.
> >
> > Changes in v4:
> > Move the delay to imx95_pcie_init_phy() with a comment added.
> >
> > Changes in v3:
> > Regarding Frank's comments, refine naming consistency and clarity.
> >
> > Changes in v2:
> > Update the register name and bit definitions.
> > Don't move IMX95_PCIE_PHY_CR_PARA_SEL settings.
> > ---
> >  drivers/pci/controller/dwc/pci-imx6.c | 32 +++++++++++++++++++++++++++
> >  1 file changed, 32 insertions(+)
> >
> > diff --git a/drivers/pci/controller/dwc/pci-imx6.c b/drivers/pci/controller/dwc/pci-imx6.c
> > index 39790e66b98dc..3bc52c4781903 100644
> > --- a/drivers/pci/controller/dwc/pci-imx6.c
> > +++ b/drivers/pci/controller/dwc/pci-imx6.c
> > @@ -80,6 +80,17 @@
> >  #define IMX95_SID_MASK				GENMASK(5, 0)
> >  #define IMX95_MAX_LUT				32
> >
> > +#define IMX95_PCIE_PHY_REG_ADDR			0x3008
> > +#define IMX95_PCIE_PHY_REG_EN			BIT(31)
> > +#define IMX95_PCIE_PHY_REG_ADDR_MASK		GENMASK(15, 0)
> > +#define IMX95_PCIE_PHY_REG_DATA			0x300c
> > +#define IMX95_PCIE_PHY_MPLLB_OVRD_IN		0x2004
> > +/* BIT(10): Override enable for mpllb_bandwidth[15:0] */
> > +#define IMX95_PCIE_PHY_MPLLB_OVRD_BW_EN		BIT(10)
> > +/* Register offset: Override value for mpllb_bandwidth[15:0] */
> > +#define IMX95_PCIE_PHY_MPLLB_BW_IN		0x2005
> > +#define IMX95_PCIE_PHY_MPLLB_BW_VAL		0x8c
> > +
> >  #define IMX95_PCIE_RST_CTRL			0x3010
> >  #define IMX95_PCIE_COLD_RST			BIT(0)
> >
> > @@ -270,6 +281,15 @@ static int imx95_pcie_select_ref_clk_src(struct imx_pcie *imx_pcie)
> >  	return 0;
> >  }
> >
> > +static void imx95_pcie_phy_write(struct imx_pcie *imx_pcie, int addr, u16 data)
> > +{
> > +	regmap_update_bits(imx_pcie->iomuxc_gpr, IMX95_PCIE_PHY_REG_ADDR,
> > +			   IMX95_PCIE_PHY_REG_EN, IMX95_PCIE_PHY_REG_EN);
> > +	regmap_update_bits(imx_pcie->iomuxc_gpr, IMX95_PCIE_PHY_REG_ADDR,
> > +			   IMX95_PCIE_PHY_REG_ADDR_MASK, addr);
> > +	regmap_write(imx_pcie->iomuxc_gpr, IMX95_PCIE_PHY_REG_DATA, data);
> > +}
> > +
> >  static int imx95_pcie_init_phy(struct imx_pcie *imx_pcie)
> >  {
> >  	/*
> > @@ -290,6 +310,18 @@ static int imx95_pcie_init_phy(struct imx_pcie *imx_pcie)
> >  			IMX95_PCIE_PHY_CR_PARA_SEL,
> >  			IMX95_PCIE_PHY_CR_PARA_SEL);
> >
>
> I've added regmap_read() to flush the IMX95_PCIE_PHY_CR_PARA_SEL update before
> below delay, while applying.

Thanks

Frank

>
> - Mani
>
> --
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