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

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Message-Id: <20250324062647.1891896-5-hongxing.zhu@nxp.com>
Date: Mon, 24 Mar 2025 14:26:46 +0800
From: Richard Zhu <hongxing.zhu@....com>
To: frank.li@....com,
	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
Cc: linux-pci@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	imx@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	Richard Zhu <hongxing.zhu@....com>
Subject: [PATCH v1 4/5] PCI: imx6: Let i.MX95 PCIe compliance with 8GT/s Receiver Impedance ECN

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