linux-kernel - Re: [PATCH v1 4/5] PCI: imx6: Let i.MX95 PCIe compliance with 8GT/s Receiver Impedance ECN

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Message-ID: <Z+GwIOBB9MwoKfpf@lizhi-Precision-Tower-5810>
Date: Mon, 24 Mar 2025 15:18:56 -0400
From: Frank Li <Frank.li@....com>
To: Richard Zhu <hongxing.zhu@....com>
Cc: l.stach@...gutronix.de, lpieralisi@...nel.org, kw@...ux.com,
	manivannan.sadhasivam@...aro.org, robh@...nel.org,
	bhelgaas@...gle.com, shawnguo@...nel.org, s.hauer@...gutronix.de,
	kernel@...gutronix.de, festevam@...il.com,
	linux-pci@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	imx@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 4/5] PCI: imx6: Let i.MX95 PCIe compliance with 8GT/s
 Receiver Impedance ECN

On Mon, Mar 24, 2025 at 02:26:46PM +0800, Richard Zhu wrote:
> Workaround for ERR051586: Compliance with 8GT/s Receiver Impedance ECN.
>
> The default value of GEN3_RELATED_OFF[GEN3_ZRXDC_NONCOMPL] is 1 which
> makes receiver non-compliant with the ZRX-DC parameter for 2.5 GT/s when
> operating at 8 GT/s or higher. It causes unnecessary timeout in L1.
>
> Workaround: Program GEN3_RELATED_OFF[GEN3_ZRXDC_NONCOMPL] to 0.
>
> Signed-off-by: Richard Zhu <hongxing.zhu@....com>
> ---
>  drivers/pci/controller/dwc/pci-imx6.c | 29 +++++++++++++++++++++++++++
>  1 file changed, 29 insertions(+)
>
> diff --git a/drivers/pci/controller/dwc/pci-imx6.c b/drivers/pci/controller/dwc/pci-imx6.c
> index 52aa8bd66cde..dda3eed99bb8 100644
> --- a/drivers/pci/controller/dwc/pci-imx6.c
> +++ b/drivers/pci/controller/dwc/pci-imx6.c
> @@ -131,6 +131,7 @@ struct imx_pcie_drvdata {
>  	int (*init_phy)(struct imx_pcie *pcie);
>  	int (*enable_ref_clk)(struct imx_pcie *pcie, bool enable);
>  	int (*core_reset)(struct imx_pcie *pcie, bool assert);
> +	void (*post_config)(struct imx_pcie *pcie);
>  	const struct dw_pcie_host_ops *ops;
>  };
>
> @@ -1158,6 +1159,29 @@ static void imx_pcie_disable_device(struct pci_host_bridge *bridge,
>  	imx_pcie_remove_lut(imx_pcie, pci_dev_id(pdev));
>  }
>
> +static void imx95_pcie_post_config(struct imx_pcie *imx_pcie)

There are already have post_init in dwc dw_pcie_host_ops

struct dw_pcie_host_ops {
        int (*init)(struct dw_pcie_rp *pp);
        void (*deinit)(struct dw_pcie_rp *pp);
        void (*post_init)(struct dw_pcie_rp *pp);
        int (*msi_init)(struct dw_pcie_rp *pp);
        void (*pme_turn_off)(struct dw_pcie_rp *pp);
};

Can you use it directly?

Frank

> +{
> +	u32 val;
> +	struct dw_pcie *pci = imx_pcie->pci;

struct dw_pcie *pci = imx_pcie->pci;
u32 val;

> +
> +	/*
> +	 * Workaround for ERR051586: Compliance with 8GT/s Receiver
> +	 * Impedance ECN
> +	 *
> +	 * The default value of GEN3_RELATED_OFF[GEN3_ZRXDC_NONCOMPL] is
> +	 * 1 which makes receiver non-compliant with the ZRX-DC
> +	 * parameter for 2.5 GT/s when operating at 8 GT/s or higher. It
> +	 * causes unnecessary timeout in L1.
> +	 *
> +	 * Workaround: Program GEN3_RELATED_OFF[GEN3_ZRXDC_NONCOMPL] to 0.
> +	 */
> +	dw_pcie_dbi_ro_wr_en(pci);
> +	val = dw_pcie_readl_dbi(pci, GEN3_RELATED_OFF);
> +	val &= ~GEN3_RELATED_OFF_GEN3_ZRXDC_NONCOMPL;
> +	dw_pcie_writel_dbi(pci, GEN3_RELATED_OFF, val);
> +	dw_pcie_dbi_ro_wr_dis(pci);
> +}
> +
>  static int imx_pcie_host_init(struct dw_pcie_rp *pp)
>  {
>  	struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
> @@ -1222,6 +1246,9 @@ static int imx_pcie_host_init(struct dw_pcie_rp *pp)
>
>  	imx_setup_phy_mpll(imx_pcie);
>
> +	if (imx_pcie->drvdata->post_config)
> +		imx_pcie->drvdata->post_config(imx_pcie);
> +
>  	return 0;
>
>  err_phy_off:
> @@ -1808,6 +1835,7 @@ static const struct imx_pcie_drvdata drvdata[] = {
>  		.mode_mask[0] = IMX95_PCIE_DEVICE_TYPE,
>  		.core_reset = imx95_pcie_core_reset,
>  		.init_phy = imx95_pcie_init_phy,
> +		.post_config = imx95_pcie_post_config,
>  	},
>  	[IMX8MQ_EP] = {
>  		.variant = IMX8MQ_EP,
> @@ -1863,6 +1891,7 @@ static const struct imx_pcie_drvdata drvdata[] = {
>  		.core_reset = imx95_pcie_core_reset,
>  		.epc_features = &imx95_pcie_epc_features,
>  		.mode = DW_PCIE_EP_TYPE,
> +		.post_config = imx95_pcie_post_config,
>  	},
>  };
>
> --
> 2.37.1
>