PCI: imx6: Assert PERST# before enabling regulators

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 prepares for an 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>
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Richard Zhu <hongxing.zhu@nxp.com>
Link: https://patch.msgid.link/20260422093549.407022-4-sherry.sun@nxp.com

diff --git a/drivers/pci/controller/dwc/pci-imx6.c b/drivers/pci/controller/dwc/pci-imx6.c
index 1034ac5c5f5c1509d4af6718148512634d67f6e6..5335c2b140fb548b3254f1cbc8fc51a5a18656e5 100644 (file)
--- 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;
 
@@ -1217,6 +1219,13 @@ 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) {
@@ -1237,6 +1246,24 @@ 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 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) {
@@ -1246,25 +1273,24 @@ 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) {
@@ -1777,9 +1803,13 @@ 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)) {