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

[Manivannan Sadhasivam]

On Mon, Aug 03, 2026 at 11:43:19AM +0800, hongxing.zhu at oss.nxp.com wrote:
> From: Richard Zhu <hongxing.zhu at 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 at nxp.com>
> Reviewed-by: Frank Li <Frank.Li at 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.

- Mani

-- 
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