linux-kernel - [PATCH] usb: dwc3: apple: Set USB2 PHY mode before dwc3 init

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Message-Id: <20260108-dwc3-apple-usb2phy-fix-v1-1-5dd7bc642040@kernel.org>
Date: Thu, 08 Jan 2026 20:21:45 +0100
From: Sven Peter <sven@...nel.org>
To: Janne Grunau <j@...nau.net>, 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, 
 James Calligeros <jcalligeros99@...il.com>, stable@...r.kernel.org, 
 Sven Peter <sven@...nel.org>
Subject: [PATCH] usb: dwc3: apple: Set USB2 PHY mode before dwc3 init

Now that the upstream code has been getting broader test coverage by our
users we occasionally see issues with USB2 devices plugged in during boot.
Before Linux is running, the USB2 PHY has usually been running in device
mode and it turns out that sometimes host->device or device->host
transitions don't work.
The root cause: If the role inside the USB2 PHY is re-configured when it
has already been powered on or when dwc2 has already enabled the ULPI
interface the new configuration sometimes doesn't take affect until dwc3
is reset again. Fix this rare issue by configuring the role much earlier.
Note that the USB3 PHY does not suffer from this issue and actually
requires dwc3 to be up before the correct role can be configured there.

Reported-by: James Calligeros <jcalligeros99@...il.com>
Reported-by: Janne Grunau <j@...nau.net>
Fixes: 0ec946d32ef7 ("usb: dwc3: Add Apple Silicon DWC3 glue layer driver")
Cc: stable@...r.kernel.org
Signed-off-by: Sven Peter <sven@...nel.org>
---
 drivers/usb/dwc3/dwc3-apple.c | 48 +++++++++++++++++++++++++++++--------------
 1 file changed, 33 insertions(+), 15 deletions(-)

diff --git a/drivers/usb/dwc3/dwc3-apple.c b/drivers/usb/dwc3/dwc3-apple.c
index cc47cad232e397ac4498b09165dfdb5bd215ded7..c2ae8eb21d514e5e493d2927bc12908c308dfe19 100644
--- a/drivers/usb/dwc3/dwc3-apple.c
+++ b/drivers/usb/dwc3/dwc3-apple.c
@@ -218,25 +218,31 @@ static int dwc3_apple_core_init(struct dwc3_apple *appledwc)
 	return ret;
 }
 
-static void dwc3_apple_phy_set_mode(struct dwc3_apple *appledwc, enum phy_mode mode)
-{
-	lockdep_assert_held(&appledwc->lock);
-
-	/*
-	 * This platform requires SUSPHY to be enabled here already in order to properly configure
-	 * the PHY and switch dwc3's PIPE interface to USB3 PHY.
-	 */
-	dwc3_enable_susphy(&appledwc->dwc, true);
-	phy_set_mode(appledwc->dwc.usb2_generic_phy[0], mode);
-	phy_set_mode(appledwc->dwc.usb3_generic_phy[0], mode);
-}
-
 static int dwc3_apple_init(struct dwc3_apple *appledwc, enum dwc3_apple_state state)
 {
 	int ret, ret_reset;
 
 	lockdep_assert_held(&appledwc->lock);
 
+	/*
+	 * The USB2 PHY on this platform must be configured for host or device mode while it is
+	 * still powered off and before dwc3 tries to access it. Otherwise, the new configuration
+	 * will sometimes only take affect after the *next* time dwc3 is brought up which causes
+	 * the connected device to just not work.
+	 * The USB3 PHY must be configured later after dwc3 has already been initialized.
+	 */
+	switch (state) {
+	case DWC3_APPLE_HOST:
+		phy_set_mode(appledwc->dwc.usb2_generic_phy[0], PHY_MODE_USB_HOST);
+		break;
+	case DWC3_APPLE_DEVICE:
+		phy_set_mode(appledwc->dwc.usb2_generic_phy[0], PHY_MODE_USB_DEVICE);
+		break;
+	default:
+		/* Unreachable unless there's a bug in this driver */
+		return -EINVAL;
+	}
+
 	ret = reset_control_deassert(appledwc->reset);
 	if (ret) {
 		dev_err(appledwc->dev, "Failed to deassert reset, err=%d\n", ret);
@@ -257,7 +263,13 @@ static int dwc3_apple_init(struct dwc3_apple *appledwc, enum dwc3_apple_state st
 	case DWC3_APPLE_HOST:
 		appledwc->dwc.dr_mode = USB_DR_MODE_HOST;
 		dwc3_apple_set_ptrcap(appledwc, DWC3_GCTL_PRTCAP_HOST);
-		dwc3_apple_phy_set_mode(appledwc, PHY_MODE_USB_HOST);
+		/*
+		 * This platform requires SUSPHY to be enabled here already in order to properly
+		 * configure the PHY and switch dwc3's PIPE interface to USB3 PHY. The USB2 PHY
+		 * has already been configured to the correct mode earlier.
+		 */
+		dwc3_enable_susphy(&appledwc->dwc, true);
+		phy_set_mode(appledwc->dwc.usb3_generic_phy[0], PHY_MODE_USB_HOST);
 		ret = dwc3_host_init(&appledwc->dwc);
 		if (ret) {
 			dev_err(appledwc->dev, "Failed to initialize host, ret=%d\n", ret);
@@ -268,7 +280,13 @@ static int dwc3_apple_init(struct dwc3_apple *appledwc, enum dwc3_apple_state st
 	case DWC3_APPLE_DEVICE:
 		appledwc->dwc.dr_mode = USB_DR_MODE_PERIPHERAL;
 		dwc3_apple_set_ptrcap(appledwc, DWC3_GCTL_PRTCAP_DEVICE);
-		dwc3_apple_phy_set_mode(appledwc, PHY_MODE_USB_DEVICE);
+		/*
+		 * This platform requires SUSPHY to be enabled here already in order to properly
+		 * configure the PHY and switch dwc3's PIPE interface to USB3 PHY. The USB2 PHY
+		 * has already been configured to the correct mode earlier.
+		 */
+		dwc3_enable_susphy(&appledwc->dwc, true);
+		phy_set_mode(appledwc->dwc.usb3_generic_phy[0], PHY_MODE_USB_DEVICE);
 		ret = dwc3_gadget_init(&appledwc->dwc);
 		if (ret) {
 			dev_err(appledwc->dev, "Failed to initialize gadget, ret=%d\n", ret);

---
base-commit: 8f0b4cce4481fb22653697cced8d0d04027cb1e8
change-id: 20260108-dwc3-apple-usb2phy-fix-cf1d26018dd0

Best regards,
-- 
Sven Peter <sven@...nel.org>