[PATCH v2 2/2] usb: dwc3: Add role switch reset quirk for Apple DWC3

[Sven Peter <sven@svenpeter.dev>]

As mad as it sounds, the dwc3 controller present on Apple SoCs must be
reset and reinitialized whenever a device is unplugged from the root port
and triggers a role switch notification from the USB PD controller.

This is required for at least two 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.

  - It's possible to completely break the dwc3 controller by switching
    it to device mode and unplugging the cable at just the wrong time.
    Even a CORESOFTRESET is not enough to allow new devices again.
    The only workaround is to trigger a hard reset of the entire
    dwc3 core. This also happens when running macOS on these
    machines.

Signed-off-by: Sven Peter <sven@svenpeter.dev>
---
v1 -> v2:
 - enable the quirk based on the compatible instead of a property
   as requested by robh

 drivers/usb/dwc3/core.c | 39 ++++++++++++++++++++++++++++++++++++---
 drivers/usb/dwc3/core.h |  6 ++++++
 drivers/usb/dwc3/drd.c  |  7 +++++++
 3 files changed, 49 insertions(+), 3 deletions(-)

diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
index 0104a80b185e..b76d7536eafe 100644
--- a/drivers/usb/dwc3/core.c
+++ b/drivers/usb/dwc3/core.c
@@ -115,6 +115,8 @@ void dwc3_set_prtcap(struct dwc3 *dwc, u32 mode)
 }
 
 static int dwc3_core_soft_reset(struct dwc3 *dwc);
+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)
 {
@@ -130,10 +132,11 @@ static void __dwc3_set_mode(struct work_struct *work)
 	if (dwc->current_dr_role == DWC3_GCTL_PRTCAP_OTG)
 		dwc3_otg_update(dwc, 0);
 
-	if (!dwc->desired_dr_role)
+	if (!dwc->desired_dr_role && !dwc->role_switch_reset_quirk)
 		goto out;
 
-	if (dwc->desired_dr_role == dwc->current_dr_role)
+	if (dwc->desired_dr_role == dwc->current_dr_role &&
+			!dwc->role_switch_reset_quirk)
 		goto out;
 
 	if (dwc->desired_dr_role == DWC3_GCTL_PRTCAP_OTG && dwc->edev)
@@ -158,6 +161,34 @@ 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 (dwc->desired_dr_role) {
+			/*
+			 * the first call to __dwc3_set_mode comes from
+			 * dwc3_drd_init. In that case dwc3_core_init has been
+			 * called but dwc->current_dr_role is zero such that
+			 * we must not reinitialize the core again here.
+			 */
+			if (dwc->role_switch_reset_quirk_initialized) {
+				ret = dwc3_core_init_for_resume(dwc);
+				if (ret) {
+					dev_err(dwc->dev,
+					    "failed to reinitialize core\n");
+					goto out;
+				}
+			}
+
+			dwc->role_switch_reset_quirk_initialized = 1;
+		} else {
+			goto out;
+		}
+	}
+
 	/* For DRD host or device mode only */
 	if (dwc->desired_dr_role != DWC3_GCTL_PRTCAP_OTG) {
 		reg = dwc3_readl(dwc->regs, DWC3_GCTL);
@@ -1586,6 +1617,8 @@ static int dwc3_probe(struct platform_device *pdev)
 		else
 			dwc->num_clks = ret;
 
+		if (of_device_is_compatible(dev->of_node, "apple,dwc3"))
+			dwc->role_switch_reset_quirk = true;
 	}
 
 	ret = reset_control_deassert(dwc->reset);
@@ -1715,7 +1748,6 @@ static int dwc3_remove(struct platform_device *pdev)
 	return 0;
 }
 
-#ifdef CONFIG_PM
 static int dwc3_core_init_for_resume(struct dwc3 *dwc)
 {
 	int ret;
@@ -1742,6 +1774,7 @@ 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)
 {
 	unsigned long	flags;
diff --git a/drivers/usb/dwc3/core.h b/drivers/usb/dwc3/core.h
index 5612bfdf37da..3fc5c5bc4c57 100644
--- a/drivers/usb/dwc3/core.h
+++ b/drivers/usb/dwc3/core.h
@@ -1080,6 +1080,9 @@ struct dwc3_scratchpad_array {
  *	3	- Reserved
  * @dis_metastability_quirk: set to disable metastability quirk.
  * @dis_split_quirk: set to disable split boundary.
+ * @role_switch_reset_quirk: set to force reinitialization after any role switch
+ * @role_switch_reset_quirk_initialized: set to true after the first role switch
+ *			which is triggered from dwc3_drd_init directly
  * @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.
@@ -1291,6 +1294,9 @@ struct dwc3 {
 	unsigned		dis_split_quirk:1;
 	unsigned		async_callbacks:1;
 
+	unsigned		role_switch_reset_quirk:1;
+	unsigned		role_switch_reset_quirk_initialized:1;
+
 	u16			imod_interval;
 
 	int			max_cfg_eps;
diff --git a/drivers/usb/dwc3/drd.c b/drivers/usb/dwc3/drd.c
index d7f76835137f..403e88a72f0e 100644
--- a/drivers/usb/dwc3/drd.c
+++ b/drivers/usb/dwc3/drd.c
@@ -506,6 +506,9 @@ 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;
 }
@@ -534,6 +537,10 @@ 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;
 }
-- 
2.25.1