linux-kernel - Re: [PATCH v3 4/6] PCI: imx6: Let i.MX95 PCIe compliance with 8GT/s Receiver Impedance ECN

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Message-ID: <u2doi5nksovsxf75ahwdr3c3uixjk555mbwouvtblf5rruoicv@uvsdytcwoish>
Date: Wed, 2 Apr 2025 12:38:35 +0530
From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To: Richard Zhu <hongxing.zhu@....com>
Cc: frank.li@....com, l.stach@...gutronix.de, lpieralisi@...nel.org, 
	kw@...ux.com, 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 v3 4/6] PCI: imx6: Let i.MX95 PCIe compliance with 8GT/s
 Receiver Impedance ECN

On Fri, Mar 28, 2025 at 11:02:11AM +0800, Richard Zhu wrote:
> 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>

Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>

- Mani

> ---
>  drivers/pci/controller/dwc/pci-imx6.c | 31 +++++++++++++++++++++++++++
>  1 file changed, 31 insertions(+)
> 
> diff --git a/drivers/pci/controller/dwc/pci-imx6.c b/drivers/pci/controller/dwc/pci-imx6.c
> index 82402e52eff2..35194b543551 100644
> --- a/drivers/pci/controller/dwc/pci-imx6.c
> +++ b/drivers/pci/controller/dwc/pci-imx6.c
> @@ -110,6 +110,7 @@ enum imx_pcie_variants {
>   */
>  #define IMX_PCIE_FLAG_BROKEN_SUSPEND		BIT(9)
>  #define IMX_PCIE_FLAG_HAS_LUT			BIT(10)
> +#define IMX_PCIE_FLAG_8GT_ECN_ERR051586		BIT(11)
>  
>  #define imx_check_flag(pci, val)	(pci->drvdata->flags & val)
>  
> @@ -1263,6 +1264,32 @@ static void imx_pcie_host_exit(struct dw_pcie_rp *pp)
>  		regulator_disable(imx_pcie->vpcie);
>  }
>  
> +static void imx_pcie_host_post_init(struct dw_pcie_rp *pp)
> +{
> +	struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
> +	struct imx_pcie *imx_pcie = to_imx_pcie(pci);
> +	u32 val;
> +
> +	if (imx_pcie->drvdata->flags & IMX_PCIE_FLAG_8GT_ECN_ERR051586) {
> +		/*
> +		 * 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 u64 imx_pcie_cpu_addr_fixup(struct dw_pcie *pcie, u64 cpu_addr)
>  {
>  	struct imx_pcie *imx_pcie = to_imx_pcie(pcie);
> @@ -1304,6 +1331,7 @@ static const struct dw_pcie_host_ops imx_pcie_host_ops = {
>  static const struct dw_pcie_host_ops imx_pcie_host_dw_pme_ops = {
>  	.init = imx_pcie_host_init,
>  	.deinit = imx_pcie_host_exit,
> +	.post_init = imx_pcie_host_post_init,
>  };
>  
>  static const struct dw_pcie_ops dw_pcie_ops = {
> @@ -1403,6 +1431,7 @@ static int imx_add_pcie_ep(struct imx_pcie *imx_pcie,
>  	struct device *dev = pci->dev;
>  
>  	imx_pcie_host_init(pp);
> +	imx_pcie_host_post_init(pp);
>  	ep = &pci->ep;
>  	ep->ops = &pcie_ep_ops;
>  
> @@ -1812,6 +1841,7 @@ static const struct imx_pcie_drvdata drvdata[] = {
>  		.variant = IMX95,
>  		.flags = IMX_PCIE_FLAG_HAS_SERDES |
>  			 IMX_PCIE_FLAG_HAS_LUT |
> +			 IMX_PCIE_FLAG_8GT_ECN_ERR051586 |
>  			 IMX_PCIE_FLAG_SUPPORTS_SUSPEND,
>  		.ltssm_off = IMX95_PE0_GEN_CTRL_3,
>  		.ltssm_mask = IMX95_PCIE_LTSSM_EN,
> @@ -1865,6 +1895,7 @@ static const struct imx_pcie_drvdata drvdata[] = {
>  	[IMX95_EP] = {
>  		.variant = IMX95_EP,
>  		.flags = IMX_PCIE_FLAG_HAS_SERDES |
> +			 IMX_PCIE_FLAG_8GT_ECN_ERR051586 |
>  			 IMX_PCIE_FLAG_SUPPORT_64BIT,
>  		.ltssm_off = IMX95_PE0_GEN_CTRL_3,
>  		.ltssm_mask = IMX95_PCIE_LTSSM_EN,
> -- 
> 2.37.1
> 

-- 
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