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

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Date:   Tue, 03 Aug 2021 10:58:37 +0300
From:   Felipe Balbi <balbi@...nel.org>
To:     Jack Pham <jackp@...eaurora.org>
Cc:     Wesley Cheng <wcheng@...eaurora.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


Jack Pham <jackp@...eaurora.org> writes:

> 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") ?

sounds like a good idea.

-- 
balbi