[PATCH v2] PCI: imx6: Fix i.MX6Q/DL boot hang by separating PHY power and reference clock control

[hongxing.zhu at oss.nxp.com]

From: Richard Zhu <hongxing.zhu at nxp.com>

Commit 610fa91d9863 ("PCI: imx6: Assert PERST# before enabling regulators")
introduced a boot hang on i.MX6Q/DL variants by changing the initialization
sequence.

The issue stems from coupling PHY power (TEST_PD) and reference clock
(REF_CLK_EN) control in imx6q_pcie_enable_ref_clk(). When these are
managed together, the timing between PHY power-up and reference clock
enablement cannot be properly controlled, leading to initialization
failures.

Fix this by separating the two concerns:

- Move PHY power control (TEST_PD) to imx6q_pcie_core_reset() where it
  logically belongs with reset operations. This ensures PHY power state
  is managed as part of the core reset sequence.

- Update imx6qp_pcie_core_reset() to call imx6q_pcie_core_reset() for
  shared PHY power management, avoiding code duplication.

- Make imx6q_pcie_enable_ref_clk() responsible only for reference clock
  (REF_CLK_EN) control, simplifying its purpose.

- Remove the 10us delay workaround from imx6q_pcie_enable_ref_clk() as
  proper sequencing is now handled by the core_reset functions.

This refactoring ensures PHY power is controlled during reset
operations, fixing the boot hang while improving code maintainability.

Fixes: 610fa91d9863 ("PCI: imx6: Assert PERST# before enabling regulators")
Signed-off-by: Richard Zhu <hongxing.zhu at nxp.com>
---
Changes in v2:
Regarding sashiko's reivew, invoke imx_pcie_assert_core_reset() explicitly
in error path of imx_pcie_host_init() and imx_pcie_host_exit().
---
 drivers/pci/controller/dwc/pci-imx6.c | 45 ++++++++++++---------------
 1 file changed, 20 insertions(+), 25 deletions(-)

diff --git a/drivers/pci/controller/dwc/pci-imx6.c b/drivers/pci/controller/dwc/pci-imx6.c
index 9406bba36953f..53f3da6ab30d5 100644
--- a/drivers/pci/controller/dwc/pci-imx6.c
+++ b/drivers/pci/controller/dwc/pci-imx6.c
@@ -680,21 +680,12 @@ static int imx_pcie_attach_pd(struct device *dev)
 
 static int imx6q_pcie_enable_ref_clk(struct imx_pcie *imx_pcie, bool enable)
 {
-	if (enable) {
-		/* power up core phy and enable ref clock */
-		regmap_clear_bits(imx_pcie->iomuxc_gpr, IOMUXC_GPR1, IMX6Q_GPR1_PCIE_TEST_PD);
-		/*
-		 * The async reset input need ref clock to sync internally,
-		 * when the ref clock comes after reset, internal synced
-		 * reset time is too short, cannot meet the requirement.
-		 * Add a ~10us delay here.
-		 */
-		usleep_range(10, 100);
-		regmap_set_bits(imx_pcie->iomuxc_gpr, IOMUXC_GPR1, IMX6Q_GPR1_PCIE_REF_CLK_EN);
-	} else {
-		regmap_clear_bits(imx_pcie->iomuxc_gpr, IOMUXC_GPR1, IMX6Q_GPR1_PCIE_REF_CLK_EN);
-		regmap_set_bits(imx_pcie->iomuxc_gpr, IOMUXC_GPR1, IMX6Q_GPR1_PCIE_TEST_PD);
-	}
+	if (enable)
+		regmap_set_bits(imx_pcie->iomuxc_gpr, IOMUXC_GPR1,
+				IMX6Q_GPR1_PCIE_REF_CLK_EN);
+	else
+		regmap_clear_bits(imx_pcie->iomuxc_gpr, IOMUXC_GPR1,
+				  IMX6Q_GPR1_PCIE_REF_CLK_EN);
 
 	return 0;
 }
@@ -823,23 +814,25 @@ static int imx6sx_pcie_core_reset(struct imx_pcie *imx_pcie, bool assert)
 	return 0;
 }
 
-static int imx6qp_pcie_core_reset(struct imx_pcie *imx_pcie, bool assert)
+static int imx6q_pcie_core_reset(struct imx_pcie *imx_pcie, bool assert)
 {
-	regmap_update_bits(imx_pcie->iomuxc_gpr, IOMUXC_GPR1, IMX6Q_GPR1_PCIE_SW_RST,
-			   assert ? IMX6Q_GPR1_PCIE_SW_RST : 0);
-	if (!assert)
-		usleep_range(200, 500);
+	if (assert)
+		regmap_set_bits(imx_pcie->iomuxc_gpr, IOMUXC_GPR1,
+				IMX6Q_GPR1_PCIE_TEST_PD);
+	else
+		regmap_clear_bits(imx_pcie->iomuxc_gpr, IOMUXC_GPR1,
+				  IMX6Q_GPR1_PCIE_TEST_PD);
 
 	return 0;
 }
 
-static int imx6q_pcie_core_reset(struct imx_pcie *imx_pcie, bool assert)
+static int imx6qp_pcie_core_reset(struct imx_pcie *imx_pcie, bool assert)
 {
+	imx6q_pcie_core_reset(imx_pcie, assert);
+	regmap_update_bits(imx_pcie->iomuxc_gpr, IOMUXC_GPR1, IMX6Q_GPR1_PCIE_SW_RST,
+			   assert ? IMX6Q_GPR1_PCIE_SW_RST : 0);
 	if (!assert)
-		return 0;
-
-	regmap_set_bits(imx_pcie->iomuxc_gpr, IOMUXC_GPR1, IMX6Q_GPR1_PCIE_TEST_PD);
-	regmap_set_bits(imx_pcie->iomuxc_gpr, IOMUXC_GPR1, IMX6Q_GPR1_PCIE_REF_CLK_EN);
+		usleep_range(200, 500);
 
 	return 0;
 }
@@ -1445,6 +1438,7 @@ static int imx_pcie_host_init(struct dw_pcie_rp *pp)
 	return 0;
 
 err_phy_off:
+	imx_pcie_assert_core_reset(imx_pcie);
 	phy_power_off(imx_pcie->phy);
 err_phy_exit:
 	phy_exit(imx_pcie->phy);
@@ -1471,6 +1465,7 @@ static void imx_pcie_host_exit(struct dw_pcie_rp *pp)
 			dev_err(pci->dev, "unable to power off PHY\n");
 		phy_exit(imx_pcie->phy);
 	}
+	imx_pcie_assert_core_reset(imx_pcie);
 	imx_pcie_clk_disable(imx_pcie);
 
 	pci_pwrctrl_power_off_devices(pci->dev);
-- 
2.34.1