Re: [PATCH v1] PCI: imx6: Update MPLLB bandwidth for i.MX95 PCIe Gen3 stability

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

On Mon, Jul 06, 2026 at 03:03:40PM +0800, hongxing.zhu@oss.nxp.com wrote:
> From: Richard Zhu <hongxing.zhu@nxp.com>

subject:
PCI: imx6: Update MPLLB bandwidth to improve i.MX95 Gen3 PCIe stability

>
> Bandwidth marginality was observed during i.MX95 Gen3 PCIe tests with
> the default MPLLB_BINDWIDTH value. This margin degradation worsens
> across voltage and temperature (VT) variations and different test
> matrices, potentially causing link stability issues.
>
> Testing with MPLLB_BINDWIDTH 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>
> ---
>  drivers/pci/controller/dwc/pci-imx6.c | 31 +++++++++++++++++++++++----
>  1 file changed, 27 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/pci/controller/dwc/pci-imx6.c b/drivers/pci/controller/dwc/pci-imx6.c
> index 6924a06bde305..023145b0dd2c7 100644
> --- a/drivers/pci/controller/dwc/pci-imx6.c
> +++ b/drivers/pci/controller/dwc/pci-imx6.c
> @@ -80,6 +80,15 @@
>  #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
> +#define IMX95_PCIE_PHY_MPLLB_BW_OVRD_EN		0x400

Not sure how spec descript it. but BW_OVRD_EN is bit of OVRD_IN register

look like IMX95_PCIE_PHY_MPLLB_OVRD_BW_EN is more clean to avoid confuse
it is a bit of register BW_OVRD_IN.

> +#define IMX95_PCIE_PHY_MPLLB_BW_OVRD_IN		0x2005
> +#define IMX95_PCIE_PHY_MPLLB_BW			0x8c
> +
>  #define IMX95_PCIE_RST_CTRL			0x3010
>  #define IMX95_PCIE_COLD_RST			BIT(0)
>
> @@ -269,6 +278,20 @@ 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_SS_RW_REG_0,
> +			   IMX95_PCIE_PHY_CR_PARA_SEL,
> +			   IMX95_PCIE_PHY_CR_PARA_SEL);
> +
> +	fsleep(200);
> +	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)
>  {
>  	/*
> @@ -284,10 +307,10 @@ static int imx95_pcie_init_phy(struct imx_pcie *imx_pcie)
>  	regmap_set_bits(imx_pcie->iomuxc_gpr, IMX95_PCIE_SS_RW_REG_1,
>  			IMX95_PCIE_SYS_AUX_PWR_DET);
>
> -	regmap_update_bits(imx_pcie->iomuxc_gpr,
> -			IMX95_PCIE_SS_RW_REG_0,
> -			IMX95_PCIE_PHY_CR_PARA_SEL,
> -			IMX95_PCIE_PHY_CR_PARA_SEL);

why need remove this part?

Frank

> +	imx95_pcie_phy_write(imx_pcie, IMX95_PCIE_PHY_MPLLB_BW_OVRD_IN,
> +			     IMX95_PCIE_PHY_MPLLB_BW);
> +	imx95_pcie_phy_write(imx_pcie, IMX95_PCIE_PHY_MPLLB_OVRD_IN,
> +			     IMX95_PCIE_PHY_MPLLB_BW_OVRD_EN);
>
>  	return 0;
>  }
> --
> 2.34.1
>
>