[PATCH v9] PCI: dwc: Don't poll L2 if skip_l23_wait is true

[Richard Zhu]

Refer to PCIe r6.0, sec 5.2, fig 5-1 Link Power Management State Flow
Diagram. Both L0 and L2/L3 Ready can be transferred to LDn directly.

It's harmless to let dw_pcie_suspend_noirq() proceed suspend after the
PME_Turn_Off is sent out, whatever the LTSSM state is in L2 or L3 after
a recommended 10ms max wait refer to PCIe r6.0, sec 5.3.3.2.1 PME
Synchronization.

The LTSSM states are inaccessible on i.MX6QP and i.MX7D after the
PME_Turn_Off is sent out.

To support this case, don't poll L2 state and apply a simple delay of
PCIE_PME_TO_L2_TIMEOUT_US(10ms) if the skip_l23_wait flag is true in
suspend.

Cc: stable at vger.kernel.org
Fixes: 4774faf854f5 ("PCI: dwc: Implement generic suspend/resume functionality")
Fixes: a528d1a72597 ("PCI: imx6: Use DWC common suspend resume method")
Signed-off-by: Richard Zhu <hongxing.zhu at nxp.com>
Reviewed-by: Frank Li <Frank.Li at nxp.com>
---
 drivers/pci/controller/dwc/pci-imx6.c             |  5 +++++
 drivers/pci/controller/dwc/pcie-designware-host.c | 15 +++++++++++++++
 drivers/pci/controller/dwc/pcie-designware.h      |  1 +
 3 files changed, 21 insertions(+)

diff --git a/drivers/pci/controller/dwc/pci-imx6.c b/drivers/pci/controller/dwc/pci-imx6.c
index 4668fc9648bf..cbe98824427b 100644
--- a/drivers/pci/controller/dwc/pci-imx6.c
+++ b/drivers/pci/controller/dwc/pci-imx6.c
@@ -114,6 +114,7 @@ enum imx_pcie_variants {
 #define IMX_PCIE_FLAG_BROKEN_SUSPEND		BIT(9)
 #define IMX_PCIE_FLAG_HAS_LUT			BIT(10)
 #define IMX_PCIE_FLAG_8GT_ECN_ERR051586		BIT(11)
+#define IMX_PCIE_FLAG_SKIP_L23_WAIT		BIT(12)
 
 #define imx_check_flag(pci, val)	(pci->drvdata->flags & val)
 
@@ -1777,6 +1778,8 @@ static int imx_pcie_probe(struct platform_device *pdev)
 		 */
 		imx_pcie_add_lut_by_rid(imx_pcie, 0);
 	} else {
+		if (imx_check_flag(imx_pcie, IMX_PCIE_FLAG_SKIP_L23_WAIT))
+			pci->pp.skip_l23_wait = true;
 		pci->pp.use_atu_msg = true;
 		ret = dw_pcie_host_init(&pci->pp);
 		if (ret < 0)
@@ -1838,6 +1841,7 @@ static const struct imx_pcie_drvdata drvdata[] = {
 		.variant = IMX6QP,
 		.flags = IMX_PCIE_FLAG_IMX_PHY |
 			 IMX_PCIE_FLAG_SPEED_CHANGE_WORKAROUND |
+			 IMX_PCIE_FLAG_SKIP_L23_WAIT |
 			 IMX_PCIE_FLAG_SUPPORTS_SUSPEND,
 		.dbi_length = 0x200,
 		.gpr = "fsl,imx6q-iomuxc-gpr",
@@ -1854,6 +1858,7 @@ static const struct imx_pcie_drvdata drvdata[] = {
 		.variant = IMX7D,
 		.flags = IMX_PCIE_FLAG_SUPPORTS_SUSPEND |
 			 IMX_PCIE_FLAG_HAS_APP_RESET |
+			 IMX_PCIE_FLAG_SKIP_L23_WAIT |
 			 IMX_PCIE_FLAG_HAS_PHY_RESET,
 		.gpr = "fsl,imx7d-iomuxc-gpr",
 		.mode_off[0] = IOMUXC_GPR12,
diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
index fad0cbedefbc..5aa7f23bb58e 100644
--- a/drivers/pci/controller/dwc/pcie-designware-host.c
+++ b/drivers/pci/controller/dwc/pcie-designware-host.c
@@ -1194,6 +1194,21 @@ int dw_pcie_suspend_noirq(struct dw_pcie *pci)
 			return ret;
 	}
 
+	/*
+	 * Skip L23 poll and wait to avoid the read hang, when LTSSM is
+	 * not powered in L2/L3/LDn properly.
+	 *
+	 * Refer to PCIe r6.0, sec 5.2, fig 5-1 Link Power Management
+	 * State Flow Diagram. Both L0 and L2/L3 Ready can be
+	 * transferred to LDn directly. On the LTSSM states poll broken
+	 * platforms, add a max 10ms delay refer to PCIe r6.0,
+	 * sec 5.3.3.2.1 PME Synchronization.
+	 */
+	if (pci->pp.skip_l23_wait) {
+		mdelay(PCIE_PME_TO_L2_TIMEOUT_US/1000);
+		goto stop_link;
+	}
+
 	ret = read_poll_timeout(dw_pcie_get_ltssm, val,
 				val == DW_PCIE_LTSSM_L2_IDLE ||
 				val <= DW_PCIE_LTSSM_DETECT_WAIT,
diff --git a/drivers/pci/controller/dwc/pcie-designware.h b/drivers/pci/controller/dwc/pcie-designware.h
index f87c67a7a482..b31f8061f23a 100644
--- a/drivers/pci/controller/dwc/pcie-designware.h
+++ b/drivers/pci/controller/dwc/pcie-designware.h
@@ -442,6 +442,7 @@ struct dw_pcie_rp {
 	struct pci_config_window *cfg;
 	bool			ecam_enabled;
 	bool			native_ecam;
+	bool                    skip_l23_wait;
 };
 
 struct dw_pcie_ep_ops {
-- 
2.37.1