linux-kernel - Re: [PATCH 1/2] usb: dwc3: gadget: Allow runtime suspend if UDC unbinded

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Message-ID: <20201029010748.GA1303156@rowland.harvard.edu>
Date:   Wed, 28 Oct 2020 21:07:48 -0400
From:   Alan Stern <stern@...land.harvard.edu>
To:     Wesley Cheng <wcheng@...eaurora.org>
Cc:     balbi@...nel.org, gregkh@...uxfoundation.org,
        Thinh.Nguyen@...opsys.com, linux-kernel@...r.kernel.org,
        linux-usb@...r.kernel.org, jackp@...eaurora.org
Subject: Re: [PATCH 1/2] usb: dwc3: gadget: Allow runtime suspend if UDC
 unbinded

On Wed, Oct 28, 2020 at 04:43:10PM -0700, Wesley Cheng wrote:
> The DWC3 runtime suspend routine checks for the USB connected parameter to
> determine if the controller can enter into a low power state.  The
> connected state is only set to false after receiving a disconnect event.
> However, in the case of a device initiated disconnect (i.e. UDC unbind),
> the controller is halted and a disconnect event is never generated.  Set
> the connected flag to false if issuing a device initiated disconnect to
> allow the controller to be suspended.
> 
> Signed-off-by: Wesley Cheng <wcheng@...eaurora.org>
> ---
>  drivers/usb/dwc3/gadget.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
> index 5d879b7606d5..6364429b2122 100644
> --- a/drivers/usb/dwc3/gadget.c
> +++ b/drivers/usb/dwc3/gadget.c
> @@ -1995,6 +1995,11 @@ static int dwc3_gadget_pullup(struct usb_gadget *g, int is_on)
>  	unsigned long		flags;
>  	int			ret;
>  
> +	if (pm_runtime_suspended(dwc->dev)) {
> +		pm_request_resume(dwc->dev);
> +		return 0;
> +	}

Isn't this racy?  What happens if the controller was active but a 
runtime suspend occurs right here?

Alan Stern

> +
>  	is_on = !!is_on;
>  
>  	/*
> @@ -2050,6 +2055,7 @@ static int dwc3_gadget_pullup(struct usb_gadget *g, int is_on)
>  			dwc->ev_buf->lpos = (dwc->ev_buf->lpos + count) %
>  						dwc->ev_buf->length;
>  		}
> +		dwc->connected = false;
>  	}
>  
>  	ret = dwc3_gadget_run_stop(dwc, is_on, false);
> -- 
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
> a Linux Foundation Collaborative Project