The PCIe endpoint may start responding or driving signals as soon as
its supply is enabled, even before the reference clock is stable.
Asserting PERST# before enabling the regulator ensures that the
endpoint remains in reset throughout the entire power-up sequence,
until both power and refclk are known to be stable and link
initialization can safely begin.

Currently, the driver enables the vpcie3v3aux regulator in
imx_pcie_probe() before PERST# is asserted in imx_pcie_host_init(),
which may cause PCIe endpoint undefined behavior during early
power-up. However, there is no issue so far because PERST# is
requested as GPIOD_OUT_HIGH in imx_pcie_probe(), which guarantees
that PERST# is asserted before enabling the vpcie3v3aux regulator.

This is prepare for the upcoming changes that will parse the reset
property using the new Root Port binding, which will use GPIOD_ASIS
when requesting the reset GPIO. With GPIOD_ASIS, the GPIO state is not
guaranteed, so explicit sequencing is required.

Fix the power sequencing by:
1. Moving vpcie3v3aux regulator enable from probe to
   imx_pcie_host_init(), where it can be properly sequenced with PERST#.
2. Moving imx_pcie_assert_perst() before regulator and clock enable to
   ensure correct ordering.

Signed-off-by: Sherry Sun <sherry.sun@nxp.com>
---
 drivers/pci/controller/dwc/pci-imx6.c | 49 +++++++++++++++++++++------
 1 file changed, 39 insertions(+), 10 deletions(-)

diff --git a/drivers/pci/controller/dwc/pci-imx6.c b/drivers/pci/controller/dwc/pci-imx6.c
index 915061ea75b9..d99da7e42590 100644
--- a/drivers/pci/controller/dwc/pci-imx6.c
+++ b/drivers/pci/controller/dwc/pci-imx6.c
@@ -168,6 +168,8 @@ struct imx_pcie {
 	u32			tx_swing_full;
 	u32			tx_swing_low;
 	struct regulator	*vpcie;
+	struct regulator	*vpcie_aux;
+	bool			vpcie_aux_enabled;
 	struct regulator	*vph;
 	void __iomem		*phy_base;
 
@@ -1222,6 +1224,13 @@ static void imx_pcie_disable_device(struct pci_host_bridge *bridge,
 	imx_pcie_remove_lut(imx_pcie, pci_dev_id(pdev));
 }
 
+static void imx_pcie_vpcie_aux_disable(void *data)
+{
+	struct regulator *vpcie_aux = data;
+
+	regulator_disable(vpcie_aux);
+}
+
 static void imx_pcie_assert_perst(struct imx_pcie *imx_pcie, bool assert)
 {
 	if (assert) {
@@ -1242,6 +1251,24 @@ static int imx_pcie_host_init(struct dw_pcie_rp *pp)
 	struct imx_pcie *imx_pcie = to_imx_pcie(pci);
 	int ret;
 
+	imx_pcie_assert_perst(imx_pcie, true);
+
+	/* Keep 3.3Vaux supply enabled for the entire PCIe controller lifecycle */
+	if (imx_pcie->vpcie_aux && !imx_pcie->vpcie_aux_enabled) {
+		ret = regulator_enable(imx_pcie->vpcie_aux);
+		if (ret) {
+			dev_err(dev, "failed to enable vpcie_aux regulator: %d\n",
+				ret);
+			return ret;
+		}
+		imx_pcie->vpcie_aux_enabled = true;
+
+		ret = devm_add_action_or_reset(dev, imx_pcie_vpcie_aux_disable,
+					       imx_pcie->vpcie_aux);
+		if (ret)
+			return ret;
+	}
+
 	if (imx_pcie->vpcie) {
 		ret = regulator_enable(imx_pcie->vpcie);
 		if (ret) {
@@ -1251,25 +1278,24 @@ static int imx_pcie_host_init(struct dw_pcie_rp *pp)
 		}
 	}
 
+	ret = imx_pcie_clk_enable(imx_pcie);
+	if (ret) {
+		dev_err(dev, "unable to enable pcie clocks: %d\n", ret);
+		goto err_reg_disable;
+	}
+
 	if (pp->bridge && imx_check_flag(imx_pcie, IMX_PCIE_FLAG_HAS_LUT)) {
 		pp->bridge->enable_device = imx_pcie_enable_device;
 		pp->bridge->disable_device = imx_pcie_disable_device;
 	}
 
 	imx_pcie_assert_core_reset(imx_pcie);
-	imx_pcie_assert_perst(imx_pcie, true);
 
 	if (imx_pcie->drvdata->init_phy)
 		imx_pcie->drvdata->init_phy(imx_pcie);
 
 	imx_pcie_configure_type(imx_pcie);
 
-	ret = imx_pcie_clk_enable(imx_pcie);
-	if (ret) {
-		dev_err(dev, "unable to enable pcie clocks: %d\n", ret);
-		goto err_reg_disable;
-	}
-
 	if (imx_pcie->phy) {
 		ret = phy_init(imx_pcie->phy);
 		if (ret) {
@@ -1782,9 +1808,12 @@ static int imx_pcie_probe(struct platform_device *pdev)
 	of_property_read_u32(node, "fsl,max-link-speed", &pci->max_link_speed);
 	imx_pcie->supports_clkreq = of_property_read_bool(node, "supports-clkreq");
 
-	ret = devm_regulator_get_enable_optional(&pdev->dev, "vpcie3v3aux");
-	if (ret < 0 && ret != -ENODEV)
-		return dev_err_probe(dev, ret, "failed to enable Vaux supply\n");
+	imx_pcie->vpcie_aux = devm_regulator_get_optional(&pdev->dev, "vpcie3v3aux");
+	if (IS_ERR(imx_pcie->vpcie_aux)) {
+		if (PTR_ERR(imx_pcie->vpcie_aux) != -ENODEV)
+			return PTR_ERR(imx_pcie->vpcie_aux);
+		imx_pcie->vpcie_aux = NULL;
+	}
 
 	imx_pcie->vpcie = devm_regulator_get_optional(&pdev->dev, "vpcie");
 	if (IS_ERR(imx_pcie->vpcie)) {
-- 
2.37.1