[PATCH v6 10/11] PCI: imx6: Add CLKREQ# override to enable REFCLK for i.MX95 PCIe

[Frank Li]

On Wed, Oct 15, 2025 at 11:04:27AM +0800, Richard Zhu wrote:
> The CLKREQ# is an open drain, active low signal that is driven low by
> the card to request reference clock. It's an optional signal added in
> PCIe CEM r4.0, sec 2. Thus, this signal wouldn't be driven low if it's
> reserved.
>
> On i.MX95 EVK board, the PCIe slot connected to the second PCIe
> controller is one standard PCIe slot. The default voltage of CLKREQ# is
> not active low, and may not be driven to active low due to the potential
> scenario listed above (e.x INTEL e1000e network card).
>
> Since the reference clock controlled by CLKREQ# is required by i.MX95
> PCIe host too. To make sure this clock is ready even when the CLKREQ#
> isn't driven low by the card(e.x the scenario described above), force
> CLKREQ# override active low for i.MX95 PCIe host to enable reference
> clock.
>
> Signed-off-by: Richard Zhu <hongxing.zhu at nxp.com>
> ---

Reviewed-by: Frank Li <Frank.Li at nxp.com>

>  drivers/pci/controller/dwc/pci-imx6.c | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
>
> diff --git a/drivers/pci/controller/dwc/pci-imx6.c b/drivers/pci/controller/dwc/pci-imx6.c
> index a60fe7c337e08..aa5a4900d0eb6 100644
> --- a/drivers/pci/controller/dwc/pci-imx6.c
> +++ b/drivers/pci/controller/dwc/pci-imx6.c
> @@ -52,6 +52,8 @@
>  #define IMX95_PCIE_REF_CLKEN			BIT(23)
>  #define IMX95_PCIE_PHY_CR_PARA_SEL		BIT(9)
>  #define IMX95_PCIE_SS_RW_REG_1			0xf4
> +#define IMX95_PCIE_CLKREQ_OVERRIDE_EN		BIT(8)
> +#define IMX95_PCIE_CLKREQ_OVERRIDE_VAL		BIT(9)
>  #define IMX95_PCIE_SYS_AUX_PWR_DET		BIT(31)
>
>  #define IMX95_PE0_GEN_CTRL_1			0x1050
> @@ -711,6 +713,22 @@ static int imx7d_pcie_enable_ref_clk(struct imx_pcie *imx_pcie, bool enable)
>  	return 0;
>  }
>
> +static void  imx95_pcie_clkreq_override(struct imx_pcie *imx_pcie, bool enable)
> +{
> +	regmap_update_bits(imx_pcie->iomuxc_gpr, IMX95_PCIE_SS_RW_REG_1,
> +			   IMX95_PCIE_CLKREQ_OVERRIDE_EN,
> +			   enable ? IMX95_PCIE_CLKREQ_OVERRIDE_EN : 0);
> +	regmap_update_bits(imx_pcie->iomuxc_gpr, IMX95_PCIE_SS_RW_REG_1,
> +			   IMX95_PCIE_CLKREQ_OVERRIDE_VAL,
> +			   enable ? IMX95_PCIE_CLKREQ_OVERRIDE_VAL : 0);
> +}
> +
> +static int imx95_pcie_enable_ref_clk(struct imx_pcie *imx_pcie, bool enable)
> +{
> +	imx95_pcie_clkreq_override(imx_pcie, enable);
> +	return 0;
> +}
> +
>  static int imx_pcie_clk_enable(struct imx_pcie *imx_pcie)
>  {
>  	struct dw_pcie *pci = imx_pcie->pci;
> @@ -1918,6 +1936,7 @@ static const struct imx_pcie_drvdata drvdata[] = {
>  		.core_reset = imx95_pcie_core_reset,
>  		.init_phy = imx95_pcie_init_phy,
>  		.wait_pll_lock = imx95_pcie_wait_for_phy_pll_lock,
> +		.enable_ref_clk = imx95_pcie_enable_ref_clk,
>  	},
>  	[IMX8MQ_EP] = {
>  		.variant = IMX8MQ_EP,
> @@ -1974,6 +1993,7 @@ static const struct imx_pcie_drvdata drvdata[] = {
>  		.core_reset = imx95_pcie_core_reset,
>  		.wait_pll_lock = imx95_pcie_wait_for_phy_pll_lock,
>  		.epc_features = &imx95_pcie_epc_features,
> +		.enable_ref_clk = imx95_pcie_enable_ref_clk,
>  		.mode = DW_PCIE_EP_TYPE,
>  	},
>  };
> --
> 2.37.1
>