usb: dwc3: Add support for Apple DWC3

As mad as it sounds, the dwc3 controller present on the Apple M1 must be
reset and reinitialized whenever a device is unplugged from the root
port or when the PHY mode is changed.

This is required for at least the following reasons:

  - The USB2 D+/D- lines are connected through a stateful eUSB2 repeater
    which in turn is controlled by a variant of the TI TPS6598x USB PD
    chip. When the USB PD controller detects a hotplug event it resets
    the eUSB2 repeater. Afterwards, no new device is recognized before
    the DWC3 core and PHY are reset as well because the eUSB2 repeater
    and the PHY/dwc3 block disagree about the current state.

  - It's possible to completely break the dwc3 controller by switching
    it to device mode and unplugging the cable at just the wrong time.
    If this happens dwc3 behaves as if no device is connected.
    CORESOFTRESET will also never clear after it has been set. The only
    workaround is to trigger a hard reset of the entire dwc3 core with
    its external reset line.

  - Whenever the PHY mode is changed (to e.g. transition to DisplayPort
    alternate mode or USB4) dwc3 has to be shutdown and reinitialized.
    Otherwise the Type-C port will not be useable until the entire SoC
    has been reset.

All of this can be easily worked around by respecting transitions to
USB_ROLE_NONE and making sure the external reset line is asserted when
switching roles.

Signed-off-by: Sven Peter <sven@svenpeter.dev>

Author: svenpeter42

drivers/usb/dwc3/core.c

@@ -143,6 +143,9 @@ void dwc3_set_prtcap(struct dwc3 *dwc, u32 mode)
 	dwc->current_dr_role = mode;
 }
 
+static void dwc3_core_exit(struct dwc3 *dwc);
+static int dwc3_core_init_for_resume(struct dwc3 *dwc);
+
 static void __dwc3_set_mode(struct work_struct *work)
 {
 	struct dwc3 *dwc = work_to_dwc(work);
@@ -162,7 +165,7 @@ static void __dwc3_set_mode(struct work_struct *work)
 	if (dwc->current_dr_role == DWC3_GCTL_PRTCAP_OTG)
 		dwc3_otg_update(dwc, 0);
 
-	if (!desired_dr_role)
+	if (!desired_dr_role && !dwc->role_switch_reset_quirk)
 		goto out;
 
 	if (desired_dr_role == dwc->current_dr_role)
@@ -190,13 +193,32 @@ static void __dwc3_set_mode(struct work_struct *work)
 		break;
 	}
 
+	if (dwc->role_switch_reset_quirk) {
+		if (dwc->current_dr_role) {
+			dwc->current_dr_role = 0;
+			dwc3_core_exit(dwc);
+		}
+
+		if (desired_dr_role) {
+			ret = dwc3_core_init_for_resume(dwc);
+			if (ret) {
+				dev_err(dwc->dev,
+				    "failed to reinitialize core\n");
+				goto out;
+			}
+		} else {
+			goto out;
+		}
+	}
+
 	/*
 	 * When current_dr_role is not set, there's no role switching.
 	 * Only perform GCTL.CoreSoftReset when there's DRD role switching.
 	 */
-	if (dwc->current_dr_role && ((DWC3_IP_IS(DWC3) ||
+	if (dwc->role_switch_reset_quirk ||
+		(dwc->current_dr_role && ((DWC3_IP_IS(DWC3) ||
 			DWC3_VER_IS_PRIOR(DWC31, 190A)) &&
-			desired_dr_role != DWC3_GCTL_PRTCAP_OTG)) {
+			desired_dr_role != DWC3_GCTL_PRTCAP_OTG))) {
 		reg = dwc3_readl(dwc->regs, DWC3_GCTL);
 		reg |= DWC3_GCTL_CORESOFTRESET;
 		dwc3_writel(dwc->regs, DWC3_GCTL, reg);
@@ -1594,6 +1616,18 @@ static int dwc3_core_init_mode(struct dwc3 *dwc)
 		ret = dwc3_drd_init(dwc);
 		if (ret)
 			return dev_err_probe(dev, ret, "failed to initialize dual-role\n");
+
+		/*
+		 * If the role switch reset quirk is required the first role
+		 * switch notification will initialize the core such that we
+		 * have to shut it down here. Make sure that the __dwc3_set_mode
+		 * queued by dwc3_drd_init has completed before since it
+		 * may still try to access MMIO.
+		 */
+		if (dwc->role_switch_reset_quirk) {
+			flush_work(&dwc->drd_work);
+			dwc3_core_exit(dwc);
+		}
 		break;
 	default:
 		dev_err(dev, "Unsupported mode of operation %d\n", dwc->dr_mode);
@@ -2171,6 +2205,22 @@ static int dwc3_probe(struct platform_device *pdev)
 	if (ret)
 		goto err_put_psy;
 
+	if (dev->of_node) {
+		if (of_device_is_compatible(dev->of_node, "apple,dwc3")) {
+			if (!IS_ENABLED(CONFIG_USB_ROLE_SWITCH) ||
+			    !IS_ENABLED(CONFIG_USB_DWC3_DUAL_ROLE)) {
+				dev_err(dev,
+				    "Apple DWC3 requires role switch support.\n"
+				    );
+				ret = -EINVAL;
+				goto err_put_psy;
+			}
+
+			dwc->dr_mode = USB_DR_MODE_OTG;
+			dwc->role_switch_reset_quirk = true;
+		}
+	}
+
 	ret = reset_control_deassert(dwc->reset);
 	if (ret)
 		goto err_put_psy;
@@ -2310,7 +2360,6 @@ static void dwc3_remove(struct platform_device *pdev)
 		power_supply_put(dwc->usb_psy);
 }
 
-#ifdef CONFIG_PM
 static int dwc3_core_init_for_resume(struct dwc3 *dwc)
 {
 	int ret;
@@ -2337,6 +2386,7 @@ static int dwc3_core_init_for_resume(struct dwc3 *dwc)
 	return ret;
 }
 
+#ifdef CONFIG_PM
 static int dwc3_suspend_common(struct dwc3 *dwc, pm_message_t msg)
 {
 	u32 reg;

drivers/usb/dwc3/core.h

@@ -1152,6 +1152,7 @@ struct dwc3_scratchpad_array {
  * @suspended: set to track suspend event due to U3/L2.
  * @susphy_state: state of DWC3_GUSB2PHYCFG_SUSPHY + DWC3_GUSB3PIPECTL_SUSPHY
  *		  before PM suspend.
+ * @role_switch_reset_quirk: set to force reinitialization after any role switch
  * @imod_interval: set the interrupt moderation interval in 250ns
  *			increments or 0 to disable.
  * @max_cfg_eps: current max number of IN eps used across all USB configs.
@@ -1386,6 +1387,8 @@ struct dwc3 {
 	unsigned		suspended:1;
 	unsigned		susphy_state:1;
 
+	unsigned		role_switch_reset_quirk:1;
+
 	u16			imod_interval;
 
 	int			max_cfg_eps;

drivers/usb/dwc3/drd.c

@@ -464,6 +464,9 @@ static int dwc3_usb_role_switch_set(struct usb_role_switch *sw,
 		break;
 	}
 
+	if (dwc->role_switch_reset_quirk && role == USB_ROLE_NONE)
+		mode = 0;
+
 	dwc3_set_mode(dwc, mode);
 	return 0;
 }
@@ -492,6 +495,10 @@ static enum usb_role dwc3_usb_role_switch_get(struct usb_role_switch *sw)
 			role = USB_ROLE_DEVICE;
 		break;
 	}
+
+	if (dwc->role_switch_reset_quirk && !dwc->current_dr_role)
+		role = USB_ROLE_NONE;
+
 	spin_unlock_irqrestore(&dwc->lock, flags);
 	return role;
 }
@@ -502,7 +509,9 @@ static int dwc3_setup_role_switch(struct dwc3 *dwc)
 	u32 mode;
 
 	dwc->role_switch_default_mode = usb_get_role_switch_default_mode(dwc->dev);
-	if (dwc->role_switch_default_mode == USB_DR_MODE_HOST) {
+	if (dwc->role_switch_reset_quirk) {
+		mode = 0;
+	} else if (dwc->role_switch_default_mode == USB_DR_MODE_HOST) {
 		mode = DWC3_GCTL_PRTCAP_HOST;
 	} else {
 		dwc->role_switch_default_mode = USB_DR_MODE_PERIPHERAL;