linux-kernel - RE: [PATCH v5 0/8] usb: dwc3: Fix broken BULK stream support to dwc3 gadget driver

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Date:   Tue, 9 Oct 2018 13:00:47 +0000
From:   Anurag Kumar Vulisha <anuragku@...inx.com>
To:     Felipe Balbi <balbi@...nel.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
CC:     "v.anuragkumar@...il.com" <v.anuragkumar@...il.com>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Thinh.Nguyen@...opsys.com" <Thinh.Nguyen@...opsys.com>,
        Ajay Yugalkishore Pandey <APANDEY@...inx.com>
Subject: RE: [PATCH v5 0/8] usb: dwc3: Fix broken BULK stream support to dwc3
 gadget driver


Hi Felipe,

>-----Original Message-----
>From: Felipe Balbi [mailto:balbi@...nel.org]
>Sent: Tuesday, October 09, 2018 12:51 PM
>To: Anurag Kumar Vulisha <anuragku@...inx.com>; gregkh@...uxfoundation.org
>Cc: v.anuragkumar@...il.com; linux-usb@...r.kernel.org; linux-
>kernel@...r.kernel.org; Thinh.Nguyen@...opsys.com; Ajay Yugalkishore Pandey
><APANDEY@...inx.com>
>Subject: RE: [PATCH v5 0/8] usb: dwc3: Fix broken BULK stream support to dwc3
>gadget driver
>
>
>Hi,
>
>Anurag Kumar Vulisha <anuragku@...inx.com> writes:
>>>> Please let us know if you have any suggestions / comments on this patch series.
>>>> If you feel this patch series are okay, can we proceed with them?
>>>
>>>I really don't like this dwc3-specific timer. The best way here would be
>>>to add a timer on udc/core.c which can be reused by any udc. This would
>>>mean, of course, teaching udc/core about streams and lettting it do part
>>>of the handling.
>>>
>>
>> Thanks for spending your time in reviewing this patch. The reason for adding the
>> timer is when streams are enabled there could be chances for the host and gadget
>> controller to become out of sync, the gadget may wait for the host to issue prime
>> transaction and the host may wait for the gadget to issue ERDY. To avoid such a
>> potential deadlock conditions, timeout needs to be implemented in dwc3 driver.
>
>"in dwc3 driver" is an implementation choice. The situation you describe
>could happen with any UDC, right?
>

Yes this could happen to other UDC drivers also, unless controller is capable of handling

>> After timeout occurs, gadget will first stop transfer and restart the transfer again.
>> This issue is mentioned in databook 2.90A section 9.5.2. I am not aware of how
>> other controllers are handling the streams, but since this issue looks more like a
>
>We should get in touch with other UDC authors. We have at least Renesas,
>net2280, bcd_udc and mtu3 supporting superspeed.
>

Thanks for pointing other drivers. Will refer these drivers to see how they are handling streams
 
>> dwc3 specific issue, I think it would be more convincing to add the timer in dwc3
>> gadget driver rather than adding in udc framework. Also we are stopping the timer
>
>why? When the situation you describe is something that can happen with
>any udc, why should we reimplement the solution on all UDCs supporting
>streams when we can give generic support for handling certain
>situations?
>

I agree with you. As you suggested will work on implementing changes in UDC

>> when a valid StreamEvnt is found, which would be difficult to handle if the timer is
>
>Why difficult? udc-core would call:
>
>mod_timer(gadget->stream_timeout_timer, msecs_to_jiffies(50));
>
>Once you receive stream event, dwc3 would call:
>
>if (timer_pending(dwc->gadget.stream_timeout_timer))
>	del_timer(dwc->gadget.stream_timeout_timer);
>
>Why is that difficult? You could even avoid anything to be written in
>dwc3 and put the del_timer() inside usb_gadget_giveback_request()
>itself. That why, dwc3 doesn't even have to know that there's a timer
>running. Also, you're timer function, instead of calling dwc3's private
>functions, should be relying on the gadget API.
>
>Your timer, apparently, should be fired per-request, then your timer
>function would call:
>
>usb_ep_dequeue(request);
>usb_ep_queue(request);
>
>If the timer expires. This would work for any UDC, not only dwc3. Then,
>this is something we document for all UDCs and they'd have to adhere to
>the API.
>
>In summary, not that many changes needed to dwc3. Nothing related to
>timers inside dwc3. Almost everythin can, and should, be done
>generically.

Thanks a lot for giving a detailed explanation. Will implement the timeout
changes into UDC core.

Best Regards,
Anurag Kumar Vulisha