Re: [PATCH] usb: dwc3: apple: Set USB2 PHY mode before dwc3 init

[Janne Grunau <j@jannau.net>]

On Thu, Jan 08, 2026 at 08:21:45PM +0100, Sven Peter wrote:
> 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

"dwc3", typo noticed by Mark Kettenis

> 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@gmail.com>
> Reported-by: Janne Grunau <j@jannau.net>
> Fixes: 0ec946d32ef7 ("usb: dwc3: Add Apple Silicon DWC3 glue layer driver")
> Cc: stable@vger.kernel.org
> Signed-off-by: Sven Peter <sven@kernel.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);
> 

Tested-by: Janne Grunau <j@jannau.net>
Reviewed-by: Janne Grunau <j@jannau.net>

Janne