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

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Message-ID: <87h8hvnuet.fsf@linux.intel.com>
Date:   Tue, 09 Oct 2018 16:04:10 +0300
From:   Felipe Balbi <balbi@...nel.org>
To:     Anurag Kumar Vulisha <anuragku@...inx.com>,
        "gregkh\@linuxfoundation.org" <gregkh@...uxfoundation.org>
Cc:     "v.anuragkumar\@gmail.com" <v.anuragkumar@...il.com>,
        "linux-usb\@vger.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
        "Thinh.Nguyen\@synopsys.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,

Anurag Kumar Vulisha <anuragku@...inx.com> writes:
>>> 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.

no problem. I just wanna make sure that this work happens in one place
and one place only :)

cheers

-- 
balbi

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