Hi Felipe, Resending... Since I am waiting on your suggestion, thought of giving remainder. Thanks, Anurag Kumar Vulisha >-----Original Message----- >From: Anurag Kumar Vulisha >Sent: Wednesday, December 12, 2018 8:41 PM >To: 'Alan Stern' <stern@xxxxxxxxxxxxxxxxxxx>; Felipe Balbi <balbi@xxxxxxxxxx> >Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>; Shuah Khan ><shuah@xxxxxxxxxx>; Johan Hovold <johan@xxxxxxxxxx>; Jaejoong Kim ><climbbb.kim@xxxxxxxxx>; Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>; >Roger Quadros <rogerq@xxxxxx>; Manu Gautam <mgautam@xxxxxxxxxxxxxx>; >martin.petersen@xxxxxxxxxx; Bart Van Assche <bvanassche@xxxxxxx>; Mike >Christie <mchristi@xxxxxxxxxx>; Matthew Wilcox <willy@xxxxxxxxxxxxx>; Colin Ian >King <colin.king@xxxxxxxxxxxxx>; linux-usb@xxxxxxxxxxxxxxx; linux- >kernel@xxxxxxxxxxxxxxx; v.anuragkumar@xxxxxxxxx; Thinh Nguyen ><thinhn@xxxxxxxxxxxx>; Tejas Joglekar <tejas.joglekar@xxxxxxxxxxxx>; Ajay >Yugalkishore Pandey <APANDEY@xxxxxxxxxx> >Subject: RE: [PATCH v7 01/10] usb: gadget: udc: Add timer support for usb requests > > >Hi Felipe, > >>-----Original Message----- >>From: Alan Stern [mailto:stern@xxxxxxxxxxxxxxxxxxx] >>Sent: Friday, December 07, 2018 10:40 PM >>To: Felipe Balbi <balbi@xxxxxxxxxx> >>Cc: Anurag Kumar Vulisha <anuragku@xxxxxxxxxx>; Greg Kroah-Hartman >><gregkh@xxxxxxxxxxxxxxxxxxx>; Shuah Khan <shuah@xxxxxxxxxx>; Johan Hovold >><johan@xxxxxxxxxx>; Jaejoong Kim <climbbb.kim@xxxxxxxxx>; Benjamin >>Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>; Roger Quadros <rogerq@xxxxxx>; >Manu >>Gautam <mgautam@xxxxxxxxxxxxxx>; martin.petersen@xxxxxxxxxx; Bart Van >>Assche <bvanassche@xxxxxxx>; Mike Christie <mchristi@xxxxxxxxxx>; Matthew >>Wilcox <willy@xxxxxxxxxxxxx>; Colin Ian King <colin.king@xxxxxxxxxxxxx>; linux- >>usb@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; v.anuragkumar@xxxxxxxxx; >>Thinh Nguyen <thinhn@xxxxxxxxxxxx>; Tejas Joglekar >><tejas.joglekar@xxxxxxxxxxxx>; Ajay Yugalkishore Pandey <APANDEY@xxxxxxxxxx> >>Subject: RE: [PATCH v7 01/10] usb: gadget: udc: Add timer support for usb requests >> >>On Fri, 7 Dec 2018, Felipe Balbi wrote: >> >>> >>> hi, >>> >>> Anurag Kumar Vulisha <anuragku@xxxxxxxxxx> writes: >>> >>Does the data book suggest a value for the timeout? >>> >> >>> > >>> > No, the databook doesn't mention about the timeout value >>> > >>> >>> >At this point, it seems that the generic approach will be messier than having >>every >>> >>> >controller driver implement its own fix. At least, that's how it appears to me. >>> >>> Why, if the UDC implementation will, anyway, be a timer? >> >>It's mostly a question of what happens when the timer expires. (After >>all, starting a timer is just as easy to do in a UDC driver as it is in >>the core.) When the timer expires, what can the core do? >> >>Don't say it can cancel the offending request and resubmit it. That >>leads to the sort of trouble we discussed earlier in this thread. In >>particular, we don't want the class driver's completion routine to be >>called when the cancel occurs. Furthermore, this leads to a race: >>Suppose the class driver decides to cancel the request at the same time >>as the core does a cancel and resubmit. Then the class driver's cancel >>could get lost and the request would remain on the UDC's queue. >> >>What you really want to do is issue the appropriate stop and restart >>commands to the hardware, while leaving the request logically active >>the entire time. The UDC core can't do this, but a UDC driver can. >> > >I agree with Alan's comment as it looks like there may be some corner cases >where the issue may occur with dequeue approach. Are you okay if the timeout >handler gets moved to the dwc3 driver (the timers still added into udc layer)? >Please let us know your suggestion on this > >Thanks, >Anurag Kumar Vulisha > >>> >>(Especially if dwc3 is the only driver affected.) >>> > >>> > As discussed above, the issue may happen with other gadgets too. As I got divide >>opinions >>> > on this implementation and both the implementations looks fine to me, I am >little >>confused >>> > on which should be implemented. >>> > >>> > @Felipe: Do you agree with Alan's implementation? Please let us know your >>suggestion >>> > on this. >>> >>> I still think a generic timer is a better solution since it has other uses. >> >>Putting a struct timer into struct usb_request is okay with me, but I >>wouldn't go any farther than that. >> >>> >>Since the purpose of the timeout is to detect a deadlock caused by a >>> >>hardware bug, I suggest a fixed and relatively short timeout value such >>> >>as one second. Cancelling and requeuing a few requests at 1-second >>> >>intervals shouldn't add very much overhead. >>> >>> I wouldn't call this a HW bug though. This is just how the UDC >>> behaves. There are N streams and host can move data in any stream at any >>> time. This means that host & gadget _can_ disagree on what stream to >>> start next. >> >>But the USB 3 spec says what should happen when the host and gadget >>disagree in this way, doesn't it? And it doesn't say that they should >>deadlock. :-) Or have I misread the spec? >> >>> One way to avoid this would be to never pre-start any streams and always >>> rely on XferNotReady, but that would mean greatly reduced throughput for >>> streams. >> >>It would be good if there was some way to actively detect the problem >>instead of passively waiting for a timer to expire. >> >>Alan Stern
