linux-kernel - Re: [PATCH v2] usb: dwc3: gadget: check drained isoc ep

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Date: Thu, 4 Apr 2024 00:29:14 +0000
From: Thinh Nguyen <Thinh.Nguyen@...opsys.com>
To: Thinh Nguyen <Thinh.Nguyen@...opsys.com>
CC: Michael Grzeschik <m.grzeschik@...gutronix.de>,
        Greg Kroah-Hartman
	<gregkh@...uxfoundation.org>,
        "linux-usb@...r.kernel.org"
	<linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] usb: dwc3: gadget: check drained isoc ep

On Tue, Apr 02, 2024, Thinh Nguyen wrote:
> On Tue, Apr 02, 2024, Thinh Nguyen wrote:
> > My concern here is for the case where transfer_in_flight == true and
> 
> I mean transfer_in_flight == false
> 
> > list_empty(started_list) == false. That means that the requests in the
> > started_list are completed but are not given back to the gadget driver.
> > 
> > Since they remained in the started_list, they will be resubmitted again
> > on the next usb_ep_queue. We may send duplicate transfers right?

Actually, since the requests are completed, the HWO bits are cleared,
nothing is submitted and no duplicate. But since the requests are not
given back yet from the started_list, then the next Start_Transfer
command will begin with the TRB address of the completed request
(HWO=0), the controller may not process the next TRBs. Have you tested
this scenario?

> > 
> > You can try to cleanup requests in the started_list, but you need to be
> > careful to make sure you're not out of sync with the transfer completion
> > events and new requests from gadget driver.
> > 

Was the problem you encounter due to no_interrupt settings where the
it was set to the last request of the uvc data pump?

if that's the case, can UVC function driver make sure to not set
no_interrupt to the last request of the data pump from the UVC?

Thanks,
Thinh