[PATCH V13 03/12] PCI: imx6: Assert PERST# before enabling regulators

Sherry Sun
2026-04-16T11:13:11Z

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 e35044cc5218..735127ed1455 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