[v3,2/2] usb: dwc3: gadget: Report isoc transfer frame number

[Felipe Balbi <balbi@kernel.org>]

Hi,

Thinh Nguyen <thinh.nguyen@synopsys.com> writes:
>>> diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
>>> index 679c12e14522..2de563124fc1 100644
>>> --- a/drivers/usb/dwc3/gadget.c
>>> +++ b/drivers/usb/dwc3/gadget.c
>>> @@ -2254,6 +2254,19 @@ static int dwc3_gadget_ep_reclaim_completed_trb(struct dwc3_ep *dep,
>>>  	if (chain && (trb->ctrl & DWC3_TRB_CTRL_HWO))
>>>  		trb->ctrl &= ~DWC3_TRB_CTRL_HWO;
>>>  
>>> +	/*
>>> +	 * For isochronous transfers, the first TRB in a service interval must
>>> +	 * have the Isoc-First type. Track and report its interval frame number.
>>> +	 */
>>> +	if (usb_endpoint_xfer_isoc(dep->endpoint.desc) &&
>>> +	    (trb->ctrl & DWC3_TRBCTL_ISOCHRONOUS_FIRST)) {
>>> +		unsigned int frame_number;
>>> +
>>> +		frame_number = DWC3_TRB_CTRL_GET_SID_SOFN(trb->ctrl);
>>> +		frame_number &= ~(dep->interval - 1);
>>> +		req->request.frame_number = frame_number;
>>> +	}
>> could you refresh my memory on how this is going to be used?
>>
>
> Sure. This informs the upper layer driver what interval the isoc request
> went out. The users can use this information for applications that
> require synchronization with the host.

Thanks. Do you have an example of a gadget that would use it? Perhaps
g_webcam can rely on this to improve its scheduling? I have this in my
testing/next already, just looking for an actual user :-)