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

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Message-ID: <20260113005221.kwl756dt3bpfelnb@synopsys.com>
Date: Tue, 13 Jan 2026 00:52:23 +0000
From: Thinh Nguyen <Thinh.Nguyen@...opsys.com>
To: Janne Grunau <j@...nau.net>
CC: Sven Peter <sven@...nel.org>, Neal Gompa <neal@...pa.dev>,
        Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "asahi@...ts.linux.dev" <asahi@...ts.linux.dev>,
        "linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH] usb: dwc3: apple: Ignore USB role switches to the active
 role

On Fri, Jan 09, 2026, Janne Grunau wrote:
> 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>
> 

Acked-by: Thinh Nguyen <Thinh.Nguyen@...opsys.com>

Thanks,
Thinh