[PATCH v2] PCI: imx6: Add suspend/resume support for i.MX6QDL

[Stefan Eichenberger]

From: Stefan Eichenberger <stefan.eichenberger@xxxxxxxxxxx>

The suspend/resume support is broken on the i.MX6QDL platform. This
patch resets the link upon resuming to recover functionality. It shares
most of the sequences with other i.MX devices but does not touch the
critical registers, which might break PCIe. This patch addresses the
same issue as the following downstream commit:
https://github.com/nxp-imx/linux-imx/commit/4e92355e1f79d225ea842511fcfd42b343b32995
In comparison this patch will also reset the device if possible. Without
this patch suspend/resume will not work if a PCIe device is connected.
The kernel will hang on resume and print an error:
ath10k_pci 0000:01:00.0: Unable to change power state from D3hot to D0, device inaccessible
8<--- cut here ---
Unhandled fault: imprecise external abort (0x1406) at 0x0106f944

Signed-off-by: Stefan Eichenberger <stefan.eichenberger@xxxxxxxxxxx>
---
v1 -> v2: Share most code with other i.MX platforms and set suspend
	  support flag for i.MX6QDL. Version 1 can be found here:
	  https://lore.kernel.org/all/20240819090428.17349-1-eichest@xxxxxxxxx/

 drivers/pci/controller/dwc/pci-imx6.c | 44 +++++++++++++++++++++++++--
 1 file changed, 41 insertions(+), 3 deletions(-)

diff --git a/drivers/pci/controller/dwc/pci-imx6.c b/drivers/pci/controller/dwc/pci-imx6.c
index 808d1f1054173..f33bef0aa1071 100644
--- a/drivers/pci/controller/dwc/pci-imx6.c
+++ b/drivers/pci/controller/dwc/pci-imx6.c
@@ -1238,8 +1238,23 @@ static int imx_pcie_suspend_noirq(struct device *dev)
 
 	imx_pcie_msi_save_restore(imx_pcie, true);
 	imx_pcie_pm_turnoff(imx_pcie);
-	imx_pcie_stop_link(imx_pcie->pci);
-	imx_pcie_host_exit(pp);
+	/*
+	 * Do not turn off the PCIe controller because of ERR003756, ERR004490, ERR005188,
+	 * they all document issues with LLTSSM and the PCIe controller which
+	 * does not come out of reset properly. Therefore, try to keep the controller enabled
+	 * and only reset the link. However, the reference clock still needs to be turned off,
+	 * else the controller will freeze on resume.
+	 */
+	if (imx_pcie->drvdata->variant == IMX6Q) {
+		/* Reset the PCIe device */
+		gpiod_set_value_cansleep(imx_pcie->reset_gpiod, 1);
+
+		if (imx_pcie->drvdata->enable_ref_clk)
+			imx_pcie->drvdata->enable_ref_clk(imx_pcie, false);
+	} else {
+		imx_pcie_stop_link(imx_pcie->pci);
+		imx_pcie_host_exit(pp);
+	}
 
 	return 0;
 }
@@ -1253,6 +1268,28 @@ static int imx_pcie_resume_noirq(struct device *dev)
 	if (!(imx_pcie->drvdata->flags & IMX_PCIE_FLAG_SUPPORTS_SUSPEND))
 		return 0;
 
+	/*
+	 * Even though the i.MX6Q does not support proper suspend/resume, we
+	 * need to reset the link after resume or the memory mapped PCIe I/O
+	 * space will be inaccessible. This will cause the system to freeze.
+	 */
+	if (imx_pcie->drvdata->variant == IMX6Q) {
+		if (imx_pcie->drvdata->enable_ref_clk)
+			imx_pcie->drvdata->enable_ref_clk(imx_pcie, true);
+
+		imx_pcie_deassert_core_reset(imx_pcie);
+
+		/*
+		 * Setup the root complex again and enable msi. Without this PCIe will
+		 * not work in msi mode and drivers will crash if they try to access
+		 * the device memory area
+		 */
+		dw_pcie_setup_rc(&imx_pcie->pci->pp);
+		imx_pcie_msi_save_restore(imx_pcie, false);
+
+		return 0;
+	}
+
 	ret = imx_pcie_host_init(pp);
 	if (ret)
 		return ret;
@@ -1485,7 +1522,8 @@ static const struct imx_pcie_drvdata drvdata[] = {
 	[IMX6Q] = {
 		.variant = IMX6Q,
 		.flags = IMX_PCIE_FLAG_IMX_PHY |
-			 IMX_PCIE_FLAG_IMX_SPEED_CHANGE,
+			 IMX_PCIE_FLAG_IMX_SPEED_CHANGE |
+			 IMX_PCIE_FLAG_SUPPORTS_SUSPEND,
 		.dbi_length = 0x200,
 		.gpr = "fsl,imx6q-iomuxc-gpr",
 		.clk_names = imx6q_clks,
-- 
2.43.0