linux-kernel - Re: [PATCH] usb: dwc3: gadget: Avoid starting DWC3 gadget during UDC unbind

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Message-ID: <87y27vai3p.fsf@kernel.org>
Date:   Fri, 17 Sep 2021 08:17:03 +0300
From:   Felipe Balbi <balbi@...nel.org>
To:     Wesley Cheng <wcheng@...eaurora.org>
Cc:     gregkh@...uxfoundation.org, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usb: dwc3: gadget: Avoid starting DWC3 gadget during
 UDC unbind


Hi,

Wesley Cheng <wcheng@...eaurora.org> writes:

> There is a race present where the DWC3 runtime resume runs in parallel
> to the UDC unbind sequence.  This will eventually lead to a possible
> scenario where we are enabling the run/stop bit, without a valid
> composition defined.
>
> Thread#1 (handling UDC unbind):
> usb_gadget_remove_driver()
> -->usb_gadget_disconnect()
>   -->dwc3_gadget_pullup(0)
> --> continue UDC unbind sequence
> -->Thread#2 is running in parallel here
>
> Thread#2 (handing next cable connect)
> __dwc3_set_mode()
>   -->pm_runtime_get_sync()
>     -->dwc3_gadget_resume()
>       -->dwc->gadget_driver is NOT NULL yet
>       -->dwc3_gadget_run_stop(1)
>       --> _dwc3gadget_start()
> ...
>
> Fix this by tracking the pullup disable routine, and avoiding resuming
> of the DWC3 gadget.  Once the UDC is re-binded, that will trigger the
> pullup enable routine, which would handle enabling the DWC3 gadget.
>
> Signed-off-by: Wesley Cheng <wcheng@...eaurora.org>

This looks okay to me, but needs to be tested by a few folks ;-)

Acked-by: Felipe Balbi <balbi@...nel.org>

-- 
balbi