Hi Alan, >-----Original Message----- >From: Alan Stern [mailto:st...@rowland.harvard.edu] >Sent: Wednesday, December 05, 2018 12:59 AM >To: Anurag Kumar Vulisha <anura...@xilinx.com> >Cc: Felipe Balbi <ba...@kernel.org>; Greg Kroah-Hartman ><gre...@linuxfoundation.org>; Shuah Khan <sh...@kernel.org>; Johan Hovold ><jo...@kernel.org>; Jaejoong Kim <climbbb....@gmail.com>; Benjamin >Herrenschmidt <b...@kernel.crashing.org>; Roger Quadros <rog...@ti.com>; Manu >Gautam <mgau...@codeaurora.org>; martin.peter...@oracle.com; Bart Van >Assche <bvanass...@acm.org>; Mike Christie <mchri...@redhat.com>; Matthew >Wilcox <wi...@infradead.org>; Colin Ian King <colin.k...@canonical.com>; linux- >u...@vger.kernel.org; linux-ker...@vger.kernel.org; v.anuragku...@gmail.com; >Thinh Nguyen <thi...@synopsys.com>; Tejas Joglekar ><tejas.jogle...@synopsys.com>; Ajay Yugalkishore Pandey <apan...@xilinx.com> >Subject: RE: [PATCH v7 01/10] usb: gadget: udc: Add timer support for usb >requests > >On Tue, 4 Dec 2018, Anurag Kumar Vulisha wrote: > >> >Is there any way for the device controller driver to detect the problem >> >without >relying >> >on a timeout? >> > >> >In fact, is this problem a known bug in the existing device controller >> >hardware? >Have >> >the controller manufacturers published a suggested scheme for working >> >around it? >> > >> >> Yes, this problem is mentioned in dwc3 controller data book and the >> workaround >> mentioned is the same that we are doing , to implement timeout and if no >> valid >> stream event is found , after timeout issue end transfer followed by start >> transfer. > >Okay. But this implies that the problem is confined to DWC3 and >doesn't affect other types of controllers, which would mean modifying >the UDC core would be inappropriate. >
Both host & gadget are equally responsible for this issue and it may potentially occur with other controllers also(which are incapable of handling this situation) . Because of this reason I would not call this issue as a dwc3 alone bug. One thing is that, with dwc3 the issue is easily reproduced. Because of these reasons I feel that it would be better to have a generic udc timers rather than having driver specific workaround. We had this same discussion earlier in this mailing list https://lkml.org/lkml/2018/10/9/638 >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. > >(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. >> With the dequeue approach there is an advantage(not related to this issue) >> that the >> class driver can have control of the timed out transfer whether to requeue >> it or >consider >> it as an error (based on implementation). This approach gives more >> flexibility to the >class >> drivers. This may be out of context of this issue but wanted to point out >> that we >may lose >> this advantage on switching to older implementation. > >Class drivers can cancel and requeue requests at any time. There's no >extra flexibility. > I agree with you, but the class drivers have to implement their own logic instead of having a generic logic to implement the timeouts. >> >Ideally it would not be necessary to rely on a timeout at all. >> > >> >Also, maintainers dislike module parameters. It would be better not to add >> >one. >> >> Okay. I would be happy if any alternative for this issue is present but >> unfortunately >> I am not able to figure out any alternative other than timers. If not >module_params() >> we can add an configfs entry in stream gadget to update the timeout. Please >provide >> your opinion on this approach. > >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. > Thanks for suggesting. 1 sec timeout should be fair enough. I will change this in next series Best Regards, Anurag Kumar Vulisha
