[PATCH v4] PCI: imx6: Fix i.MX6Q/DL boot hang caused by improper PHY power sequencing

From: Richard Zhu <[email protected]>

Commit 610fa91d9863 ("PCI: imx6: Assert PERST# before enabling regulators")
introduced a boot hang on i.MX6Q/DL variants by reordering the
initialization sequence, which exposed a critical PHY power control issue.

Root cause:
Before commit 610fa91d9863 ("PCI: imx6: Assert PERST# before enabling regulators"),
the sequence was:
  1. imx_pcie_assert_core_reset() - asserts TEST_PD, asserts REF_CLK_EN
  2. imx_pcie_clk_enable() - clears TEST_PD, asserts REF_CLK_EN
  3. Link training starts with TEST_PD properly cleared ✓

After commit 610fa91d9863 ("PCI: imx6: Assert PERST# before enabling regulators"),
the sequence became:
  1. imx_pcie_clk_enable() - clears TEST_PD, asserts REF_CLK_EN
  2. imx_pcie_assert_core_reset() - re-asserts TEST_PD, asserts REF_CLK_EN
  3. imx_pcie_deassert_core_reset() - does NOT clear TEST_PD
  4. Link training starts with TEST_PD still asserted ✗

The reordering caused TEST_PD to be cleared prematurely in clk_enable(),
then re-asserted by assert_core_reset(), and never cleared again before
link training, resulting in the boot hang.

The fix requires two interdependent changes that cannot be split:
1. Move TEST_PD control to imx6q_pcie_core_reset() where it belongs
   logically with reset operations
2. Remove TEST_PD manipulation from imx6q_pcie_enable_ref_clk() to
   prevent premature clearing

Applying only change #1 results in device detection failure because
TEST_PD gets cleared too early in clk_enable(), then re-asserted in
assert_core_reset(), then cleared again in deassert_core_reset(). This
premature clearing disrupts the proper PHY power-up sequence.

Both changes together ensure the correct sequence:
  1. REF_CLK_EN asserted in clk_enable() (TEST_PD untouched)
  2. TEST_PD asserted in assert_core_reset()
  3. TEST_PD cleared in deassert_core_reset()
  4. Link training starts with proper PHY state ✓

The previous delay in imx6q_pcie_enable_ref_clk() was a workaround for
async reset synchronization when ref clock and PHY power were coupled.
With proper sequencing, this delay is no longer needed.

The i.MX6Q/DL PCIe PHY requires approximately 120us between TEST_PD
de-assertion and link training start. Add usleep_range(200, 500) in
imx6q_pcie_core_reset() after clearing TEST_PD to satisfy this
requirement.

Additional changes:
Add explicit imx_pcie_assert_core_reset() calls in error paths and
host_exit() to ensure no power leak.

Fixes: 610fa91d9863 ("PCI: imx6: Assert PERST# before enabling regulators")
Signed-off-by: Richard Zhu <[email protected]>
Reported-by: Leonardo Costa <[email protected]>
Closes: https://lore.kernel.org/lkml/[email protected]/
Tested-by: Leonardo Costa <[email protected]>
Reviewed-by: Frank Li <[email protected]>
---
Changes in v4:
Refer to Sashiko' reivew of v3 patch.
- Adjust imx_pcie_assert_core_reset() in imx_pcie_host_exit().
- Add the delay explicitly after TEST_PD is cleared, since the PERST# GPIO
might be optional.

Changes in v3:
Update the commit descriptions to address the following items.
- Clarify the root cause of this regresssion.
- Describe why both changes are mandatory required to fix this
  regression.
- Justify the delay removal also.

Changes in v2:
Per Sashiko's review, 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 | 41 ++++++++++++++-------------
 1 file changed, 22 insertions(+), 19 deletions(-)

diff --git a/drivers/pci/controller/dwc/pci-imx6.c b/drivers/pci/controller/dwc/pci-imx6.c
index e25f938eefe23..c94b5e991aecd 100644
--- a/drivers/pci/controller/dwc/pci-imx6.c
+++ b/drivers/pci/controller/dwc/pci-imx6.c
@@ -681,21 +681,12 @@ 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;
 }
@@ -826,6 +817,12 @@ static int imx6sx_pcie_core_reset(struct imx_pcie *imx_pcie, bool assert)
 
 static int imx6qp_pcie_core_reset(struct imx_pcie *imx_pcie, bool assert)
 {
+	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);
 	regmap_update_bits(imx_pcie->iomuxc_gpr, IOMUXC_GPR1, IMX6Q_GPR1_PCIE_SW_RST,
 			   assert ? IMX6Q_GPR1_PCIE_SW_RST : 0);
 	if (!assert)
@@ -836,11 +833,15 @@ 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)
 {
-	if (!assert)
-		return 0;
+	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);
 
-	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);
+	if (!assert)
+		usleep_range(200, 500);
 
 	return 0;
 }
@@ -1451,6 +1452,7 @@ 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);
@@ -1470,6 +1472,7 @@ static void imx_pcie_host_exit(struct dw_pcie_rp *pp)
 	struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
 	struct imx_pcie *imx_pcie = to_imx_pcie(pci);
 
+	imx_pcie_assert_core_reset(imx_pcie);
 	if (imx_pcie->phy) {
 		if (phy_power_off(imx_pcie->phy))
 			dev_err(pci->dev, "unable to power off PHY\n");
-- 
2.34.1