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

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Date:   Sat, 13 Nov 2021 12:05:52 +0100
From:   Janne Grunau <j@...nau.net>
To:     Sven Peter <sven@...npeter.dev>
Cc:     Felipe Balbi <balbi@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Hector Martin <marcan@...can.st>,
        Alyssa Rosenzweig <alyssa@...enzweig.io>,
        Mark Kettenis <mark.kettenis@...all.nl>,
        Rob Herring <robh+dt@...nel.org>, linux-usb@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] usb: dwc3: Add role switch reset quirk for Apple
 DWC3

On 2021-11-08 18:09:46 +0100, Sven Peter wrote:
> 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.

This patch is necessary and works on M1 Max (Macbook Pro 14" 2021).  
Tested with compatible = "apple,t6000,dwc3", "apple,dwc3", "snps,dwc3";.

Feel free to add

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

Janne