linux-kernel - Re: [PATCH] usb: dwc3: gadget: Avoid runtime resume if disabling pullup

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Date:   Mon, 2 Aug 2021 14:33:01 -0700
From:   Jack Pham <jackp@...eaurora.org>
To:     Wesley Cheng <wcheng@...eaurora.org>
Cc:     balbi@...nel.org, gregkh@...uxfoundation.org,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usb: dwc3: gadget: Avoid runtime resume if disabling
 pullup

Hi Wesley,

On Fri, Jul 30, 2021 at 05:29:34PM -0700, Wesley Cheng wrote:
> If the device is already in the runtime suspended state, any call to
> the pullup routine will issue a runtime resume on the DWC3 core
> device.  If the USB gadget is disabling the pullup, then avoid having
> to issue a runtime resume, as DWC3 gadget has already been
> halted/stopped.
> 
> This fixes an issue where the following condition occurs:
> 
> usb_gadget_remove_driver()
> -->usb_gadget_disconnect()
>  -->dwc3_gadget_pullup(0)
>   -->pm_runtime_get_sync() -> ret = 0
>   -->pm_runtime_put() [async]
> -->usb_gadget_udc_stop()
>  -->dwc3_gadget_stop()
>   -->dwc->gadget_driver = NULL
> ...
> 
> dwc3_suspend_common()
> -->dwc3_gadget_suspend()
>  -->DWC3 halt/stop routine skipped, driver_data == NULL
> 
> This leads to a situation where the DWC3 gadget is not properly
> stopped, as the runtime resume would have re-enabled EP0 and event
> interrupts, and since we avoided the DWC3 gadget suspend, these
> resources were never disabled.
> 
> Signed-off-by: Wesley Cheng <wcheng@...eaurora.org>
> ---
>  drivers/usb/dwc3/gadget.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
> index a29a4ca..5d08454 100644
> --- a/drivers/usb/dwc3/gadget.c
> +++ b/drivers/usb/dwc3/gadget.c
> @@ -2435,6 +2435,17 @@ static int dwc3_gadget_pullup(struct usb_gadget *g, int is_on)
>  	}
>  
>  	/*
> +	 * Avoid issuing a runtime resume if the device is already in the
> +	 * suspended state during gadget disconnect.  DWC3 gadget was already
> +	 * halted/stopped during runtime suspend.
> +	 */
> +	if (!is_on) {
> +		pm_runtime_barrier(dwc->dev);
> +		if (pm_runtime_suspended(dwc->dev))
> +			return 0;
> +	}
> +
> +	/*
>  	 * Check the return value for successful resume, or error.  For a
>  	 * successful resume, the DWC3 runtime PM resume routine will handle
>  	 * the run stop sequence, so avoid duplicate operations here.

Should this also go to stable with Fixes: 77adb8bdf422 ("usb: dwc3:
gadget: Allow runtime suspend if UDC unbinded") ?

Jack