usb: dwc2: Implement recovery after PM domain off

According to the dt-bindings there are some platforms, which have a
dedicated USB power domain for DWC2 IP core supply. If the power domain
is switched off during system suspend then all USB register will lose
their settings.

Use GUSBCFG_TOUTCAL as a canary to detect that the power domain has
been powered off during suspend. Since the GOTGCTL_CURMODE_HOST doesn't
match on all platform with the current mode, additionally backup
GINTSTS. This works reliable to decide which registers should be
restored.

Signed-off-by: Stefan Wahren <wahrenst@gmx.net>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Link: https://lore.kernel.org/r/20250217134132.36786-4-wahrenst@gmx.net
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: lategoodbye

drivers/usb/dwc2/core.c

@@ -43,6 +43,7 @@ int dwc2_backup_global_registers(struct dwc2_hsotg *hsotg)
 	/* Backup global regs */
 	gr = &hsotg->gr_backup;
 
+	gr->gintsts = dwc2_readl(hsotg, GINTSTS);
 	gr->gotgctl = dwc2_readl(hsotg, GOTGCTL);
 	gr->gintmsk = dwc2_readl(hsotg, GINTMSK);
 	gr->gahbcfg = dwc2_readl(hsotg, GAHBCFG);

drivers/usb/dwc2/core.h

@@ -667,6 +667,7 @@ struct dwc2_hw_params {
 /**
  * struct dwc2_gregs_backup - Holds global registers state before
  * entering partial power down
+ * @gintsts:		Backup of GINTSTS register
  * @gotgctl:		Backup of GOTGCTL register
  * @gintmsk:		Backup of GINTMSK register
  * @gahbcfg:		Backup of GAHBCFG register
@@ -683,6 +684,7 @@ struct dwc2_hw_params {
  * @valid:		True if registers values backuped.
  */
 struct dwc2_gregs_backup {
+	u32 gintsts;
 	u32 gotgctl;
 	u32 gintmsk;
 	u32 gahbcfg;

drivers/usb/dwc2/platform.c

@@ -685,6 +685,14 @@ static int __maybe_unused dwc2_suspend(struct device *dev)
 		regulator_disable(dwc2->usb33d);
 	}
 
+	if (is_device_mode)
+		ret = dwc2_gadget_backup_critical_registers(dwc2);
+	else
+		ret = dwc2_host_backup_critical_registers(dwc2);
+
+	if (ret)
+		return ret;
+
 	if (dwc2->ll_hw_enabled &&
 	    (is_device_mode || dwc2_host_can_poweroff_phy(dwc2))) {
 		ret = __dwc2_lowlevel_hw_disable(dwc2);
@@ -694,6 +702,24 @@ static int __maybe_unused dwc2_suspend(struct device *dev)
 	return ret;
 }
 
+static int dwc2_restore_critical_registers(struct dwc2_hsotg *hsotg)
+{
+	struct dwc2_gregs_backup *gr;
+
+	gr = &hsotg->gr_backup;
+
+	if (!gr->valid) {
+		dev_err(hsotg->dev, "No valid register backup, failed to restore\n");
+		return -EINVAL;
+	}
+
+	if (gr->gintsts & GINTSTS_CURMODE_HOST)
+		return dwc2_host_restore_critical_registers(hsotg);
+
+	return dwc2_gadget_restore_critical_registers(hsotg, DWC2_RESTORE_DCTL |
+						      DWC2_RESTORE_DCFG);
+}
+
 static int __maybe_unused dwc2_resume(struct device *dev)
 {
 	struct dwc2_hsotg *dwc2 = dev_get_drvdata(dev);
@@ -706,6 +732,18 @@ static int __maybe_unused dwc2_resume(struct device *dev)
 	}
 	dwc2->phy_off_for_suspend = false;
 
+	/*
+	 * During suspend it's possible that the power domain for the
+	 * DWC2 controller is disabled and all register values get lost.
+	 * In case the GUSBCFG register is not initialized, it's clear the
+	 * registers must be restored.
+	 */
+	if (!(dwc2_readl(dwc2, GUSBCFG) & GUSBCFG_TOUTCAL_MASK)) {
+		ret = dwc2_restore_critical_registers(dwc2);
+		if (ret)
+			return ret;
+	}
+
 	if (dwc2->params.activate_stm_id_vb_detection) {
 		unsigned long flags;
 		u32 ggpio, gotgctl;