linux-kernel - [PATCH] usb: dwc3: apple: Ignore USB role switches to the active role

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Message-Id: <20260109-apple-dwc3-role-switch-v1-1-11623b0f6222@jannau.net>
Date: Fri, 09 Jan 2026 11:13:48 +0100
From: Janne Grunau <j@...nau.net>
To: Sven Peter <sven@...nel.org>, Neal Gompa <neal@...pa.dev>, 
 Thinh Nguyen <Thinh.Nguyen@...opsys.com>, 
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: asahi@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org, 
 linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org, 
 stable@...r.kernel.org, Janne Grunau <j@...nau.net>
Subject: [PATCH] usb: dwc3: apple: Ignore USB role switches to the active
 role

Ignore USB role switches if dwc3-apple is already in the desired state.
The USB-C port controller on M2 and M1/M2 Pro/Max/Ultra devices issues
additional interrupts which result in USB role switches to the already
active role.
Ignore these USB role switches to ensure the USB-C port controller and
dwc3-apple are always in a consistent state. This matches the behaviour
in __dwc3_set_mode() in core.c.
Fixes detecting USB 2.0 and 3.x devices on the affected systems. The
reset caused by the additional role switch appears to leave the USB
devices in a state which prevents detection when the phy and dwc3 is
brought back up again.

Fixes: 0ec946d32ef7 ("usb: dwc3: Add Apple Silicon DWC3 glue layer driver")
Cc: stable@...r.kernel.org
Signed-off-by: Janne Grunau <j@...nau.net>
---
 drivers/usb/dwc3/dwc3-apple.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/drivers/usb/dwc3/dwc3-apple.c b/drivers/usb/dwc3/dwc3-apple.c
index cc47cad232e397ac4498b09165dfdb5bd215ded7..35eadd1fa08049829ba40651a96eb122ed55460f 100644
--- a/drivers/usb/dwc3/dwc3-apple.c
+++ b/drivers/usb/dwc3/dwc3-apple.c
@@ -339,6 +339,22 @@ static int dwc3_usb_role_switch_set(struct usb_role_switch *sw, enum usb_role ro
 
 	guard(mutex)(&appledwc->lock);
 
+	/*
+	 * Skip role switches if appledwc is already in the desired state. The
+	 * USB-C port controller on M2 and M1/M2 Pro/Max/Ultra devices issues
+	 * additional interrupts which results in usb_role_switch_set_role()
+	 * calls with the current role.
+	 * Ignore those calls here to ensure the USB-C port controller and
+	 * appledwc are in a consistent state.
+	 * This matches the behaviour in __dwc3_set_mode().
+	 * Do no handle USB_ROLE_NONE for DWC3_APPLE_NO_CABLE and
+	 * DWC3_APPLE_PROBE_PENDING since that is no-op anyway.
+	 */
+	if (appledwc->state == DWC3_APPLE_HOST && role == USB_ROLE_HOST)
+		return 0;
+	if (appledwc->state == DWC3_APPLE_DEVICE && role == USB_ROLE_DEVICE)
+		return 0;
+
 	/*
 	 * We need to tear all of dwc3 down and re-initialize it every time a cable is
 	 * connected or disconnected or when the mode changes. See the documentation for enum

---
base-commit: 8f0b4cce4481fb22653697cced8d0d04027cb1e8
change-id: 20260109-apple-dwc3-role-switch-1b684f73860c

Best regards,
-- 
Janne Grunau <j@...nau.net>