linux-kernel - [PATCH v1 2/2] PCI: imx6: Add a method to handle CLKREQ# override active low

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Message-Id: <20250820081048.2279057-3-hongxing.zhu@nxp.com>
Date: Wed, 20 Aug 2025 16:10:48 +0800
From: Richard Zhu <hongxing.zhu@....com>
To: frank.li@....com,
	l.stach@...gutronix.de,
	lpieralisi@...nel.org,
	kwilczynski@...nel.org,
	mani@...nel.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 2/2] PCI: imx6: Add a method to handle CLKREQ# override active low

The CLKREQ# is an open drain, active low signal that is driven low by
the card to request reference clock.

Since the reference clock may be required by i.MX PCIe host too. To make
sure this clock is available even when the CLKREQ# isn't driven low by
the card(e.x no card connected), force CLKREQ# override active low for
i.MX PCIe host during initialization.

The CLKREQ# override can be cleared safely when supports-clkreq is
present and PCIe link is up later. Because the CLKREQ# would be driven
low by the card in this case.

Signed-off-by: Richard Zhu <hongxing.zhu@....com>
---
 drivers/pci/controller/dwc/pci-imx6.c | 35 +++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/drivers/pci/controller/dwc/pci-imx6.c b/drivers/pci/controller/dwc/pci-imx6.c
index 80e48746bbaf6..a73632b47e2d3 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
@@ -136,6 +138,7 @@ struct imx_pcie_drvdata {
 	int (*enable_ref_clk)(struct imx_pcie *pcie, bool enable);
 	int (*core_reset)(struct imx_pcie *pcie, bool assert);
 	int (*wait_pll_lock)(struct imx_pcie *pcie);
+	void (*clr_clkreq_override)(struct imx_pcie *pcie);
 	const struct dw_pcie_host_ops *ops;
 };
 
@@ -149,6 +152,7 @@ struct imx_pcie {
 	struct gpio_desc	*reset_gpiod;
 	struct clk_bulk_data	*clks;
 	int			num_clks;
+	bool			supports_clkreq;
 	struct regmap		*iomuxc_gpr;
 	u16			msi_ctrl;
 	u32			controller_id;
@@ -267,6 +271,13 @@ static int imx95_pcie_init_phy(struct imx_pcie *imx_pcie)
 			   IMX95_PCIE_REF_CLKEN,
 			   IMX95_PCIE_REF_CLKEN);
 
+	/* Force CLKREQ# low by override */
+	regmap_update_bits(imx_pcie->iomuxc_gpr,
+			   IMX95_PCIE_SS_RW_REG_1,
+			   IMX95_PCIE_CLKREQ_OVERRIDE_EN |
+			   IMX95_PCIE_CLKREQ_OVERRIDE_VAL,
+			   IMX95_PCIE_CLKREQ_OVERRIDE_EN |
+			   IMX95_PCIE_CLKREQ_OVERRIDE_VAL);
 	return 0;
 }
 
@@ -1298,6 +1309,18 @@ static void imx_pcie_host_exit(struct dw_pcie_rp *pp)
 		regulator_disable(imx_pcie->vpcie);
 }
 
+static void imx8mm_pcie_clr_clkreq_override(struct imx_pcie *imx_pcie)
+{
+	imx8mm_pcie_enable_ref_clk(imx_pcie, false);
+}
+
+static void imx95_pcie_clr_clkreq_override(struct imx_pcie *imx_pcie)
+{
+	regmap_update_bits(imx_pcie->iomuxc_gpr, IMX95_PCIE_SS_RW_REG_1,
+			   IMX95_PCIE_CLKREQ_OVERRIDE_EN |
+			   IMX95_PCIE_CLKREQ_OVERRIDE_VAL, 0);
+}
+
 static void imx_pcie_host_post_init(struct dw_pcie_rp *pp)
 {
 	struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
@@ -1322,6 +1345,12 @@ static void imx_pcie_host_post_init(struct dw_pcie_rp *pp)
 		dw_pcie_writel_dbi(pci, GEN3_RELATED_OFF, val);
 		dw_pcie_dbi_ro_wr_dis(pci);
 	}
+
+	/* Clear CLKREQ# override if supports_clkreq is true and link is up */
+	if (dw_pcie_link_up(pci) && imx_pcie->supports_clkreq) {
+		if (imx_pcie->drvdata->clr_clkreq_override)
+			imx_pcie->drvdata->clr_clkreq_override(imx_pcie);
+	}
 }
 
 /*
@@ -1745,6 +1774,8 @@ static int imx_pcie_probe(struct platform_device *pdev)
 	pci->max_link_speed = 1;
 	of_property_read_u32(node, "fsl,max-link-speed", &pci->max_link_speed);
 
+	imx_pcie->supports_clkreq =
+		of_property_read_bool(node, "supports-clkreq");
 	imx_pcie->vpcie = devm_regulator_get_optional(&pdev->dev, "vpcie");
 	if (IS_ERR(imx_pcie->vpcie)) {
 		if (PTR_ERR(imx_pcie->vpcie) != -ENODEV)
@@ -1873,6 +1904,7 @@ static const struct imx_pcie_drvdata drvdata[] = {
 		.mode_mask[1] = IMX8MQ_GPR12_PCIE2_CTRL_DEVICE_TYPE,
 		.init_phy = imx8mq_pcie_init_phy,
 		.enable_ref_clk = imx8mm_pcie_enable_ref_clk,
+		.clr_clkreq_override = imx8mm_pcie_clr_clkreq_override,
 	},
 	[IMX8MM] = {
 		.variant = IMX8MM,
@@ -1883,6 +1915,7 @@ static const struct imx_pcie_drvdata drvdata[] = {
 		.mode_off[0] = IOMUXC_GPR12,
 		.mode_mask[0] = IMX6Q_GPR12_DEVICE_TYPE,
 		.enable_ref_clk = imx8mm_pcie_enable_ref_clk,
+		.clr_clkreq_override = imx8mm_pcie_clr_clkreq_override,
 	},
 	[IMX8MP] = {
 		.variant = IMX8MP,
@@ -1893,6 +1926,7 @@ static const struct imx_pcie_drvdata drvdata[] = {
 		.mode_off[0] = IOMUXC_GPR12,
 		.mode_mask[0] = IMX6Q_GPR12_DEVICE_TYPE,
 		.enable_ref_clk = imx8mm_pcie_enable_ref_clk,
+		.clr_clkreq_override = imx8mm_pcie_clr_clkreq_override,
 	},
 	[IMX8Q] = {
 		.variant = IMX8Q,
@@ -1913,6 +1947,7 @@ 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,
+		.clr_clkreq_override = imx95_pcie_clr_clkreq_override,
 	},
 	[IMX8MQ_EP] = {
 		.variant = IMX8MQ_EP,
-- 
2.37.1