On 5/4/2021 6:50 PM, Thinh Nguyen wrote: > Wesley Cheng wrote: >> >> >> On 5/3/2021 10:22 PM, Thinh Nguyen wrote: >>> Wesley Cheng wrote: >>>> >>>> >>>> On 5/3/2021 8:12 PM, Thinh Nguyen wrote: >>>>> Hi Wesley, >>>>> >>>>> Wesley Cheng wrote: >>>>>> >>>>>> >>>>>> On 5/3/2021 7:20 PM, Thinh Nguyen wrote: >>>>>>> Hi, >>>>>>> >>>>>>> Wesley Cheng wrote: >>>>>>>> If an error is received when issuing a start or update transfer >>>>>>>> command, the error handler will stop all active requests (including >>>>>>>> the current USB request), and call dwc3_gadget_giveback() to notify >>>>>>>> function drivers of the requests which have been stopped. Avoid >>>>>>>> having to cancel the current request which is trying to be queued, as >>>>>>>> the function driver will handle the EP queue error accordingly. >>>>>>>> Simply unmap the request as it was done before, and allow previously >>>>>>>> started transfers to be cleaned up. >>>>>>>> >>>>>> >>>>>> Hi Thinh, >>>>>> >>>>>>> >>>>>>> It looks like you're still letting dwc3 stopping and cancelling all the >>>>>>> active requests instead letting the function driver doing the dequeue. >>>>>>> >>>>>> >>>>>> Yeah, main issue isn't due to the function driver doing dequeue, but >>>>>> having cleanup (ie USB request free) if there is an error during >>>>>> usb_ep_queue(). >>>>>> >>>>>> The function driver in question at the moment is the f_fs driver in AIO >>>>>> mode. When async IO is enabled in the FFS driver, every time it queues >>>>>> a packet, it will allocate a io_data struct beforehand. If the >>>>>> usb_ep_queue() fails it will free this io_data memory. Problem is that, >>>>>> since the DWC3 gadget calls the completion with -ECONNRESET, the FFS >>>>>> driver will also schedule a work item (within io_data struct) to handle >>>>>> the completion. So you end up with a flow like below >>>>>> >>>>>> allocate io_data (ffs) >>>>>> --> usb_ep_queue() >>>>>> --> __dwc3_gadget_kick_transfer() >>>>>> --> dwc3_send_gadget_ep_cmd(EINVAL) >>>>>> --> dwc3_gadget_ep_cleanup_cancelled_requests() >>>>>> --> dwc3_gadget_giveback(ECONNRESET) >>>>>> ffs completion callback >>>>>> queue work item within io_data >>>>>> --> usb_ep_queue returns EINVAL >>>>>> ffs frees io_data >>>>>> ... >>>>>> >>>>>> work scheduled >>>>>> --> NULL pointer/memory fault as io_data is freed >>>> >>>> Hi Thinh, >>>> >>>>> >>>>> sounds like a race issue. >>>>> >>>> >>>> It'll always happen if usb_ep_queue() fails with an error. Sorry for not >>>> clarifying, but the "..." represents executing in a different context >>>> :). Anything above the "..." is in the same context. >>>>>> >>>>>>> BTW, what kinds of command and error do you see in your setup and for >>>>>>> what type endpoint? I'm thinking of letting the function driver to >>>>>>> dequeue the requests instead of letting dwc3 automatically >>>>>>> ending/cancelling the queued requests. However, it's a bit tricky to do >>>>>>> that if the error is -ETIMEDOUT since we're not sure if the controller >>>>>>> had already cached the TRBs. >>>>>>> >>>>>> >>>>>> Happens on bulk EPs so far, but I think it wouldn't matter as long as >>>>>> its over the FFS interface. (and using async IO transfers) >>>>> >>>>> Do you know which command and error code? It's strange if >>>>> UPDATE_TRANSFER command failed. >>>>> >>>> >>>> Sorry for missing that part of the question. It is a no xfer resource >>>> error on a start transfer command. So far this happens on low system >>>> memory test cases, so there may be some sequences that were missed, >>>> which led to this particular command error. >>>> >>>> Thanks >>>> Wesley Cheng >> >> Hi Thinh, >> >>> >>> No xfer resource usually means that the driver attempted to send >>> START_TRANSFER without waiting for END_TRANSFER command to complete. >>> This may be a dwc3 driver issue. Did you check this? >>> >>> Thanks, >>> Thinh >>> >>> >> >> Yes, we know the reason why this happens, and its due to one of the >> downstream changes we had that led to the scenario above. Although, >> that has been fixed, I still believe the error path is a potential >> scenario we'd still want to address. >> >> I think the returning success always on dwc3_gadget_ep_queue(), and >> allowing the error in the completion handler/giveback at the function >> driver level to do the cleanup is a feasible solution. Doesn't change >> the flow of the DWC3 gadget, and so far all function drivers we've used >> handle this in the correct manner. >> >> Thanks >> Wesley Cheng > > Right. I think for now we should do that (return success always except > for cases of disconnect or already in-flight etc). This helps keeping it > simple and avoid some pitfalls dealing with giving back the request. > Currently we return the error status to dwc3_gadget_ep_queue if we > failed to send a command that may not even related to the same request > being queued. > > This way, I think it matches with how we handle it in the driver. We > always put the request in the pending list (queued) first and possibly > start/update the controller with new data. > > Thanks, > Thinh > > Hi Thinh, Agreed, thanks for the input and in depth discussion. Will spin a new revision with the suggestion above. Thanks Wesley Cheng >> >>>> >>>>>> >>>>>>> This seems to add more complexity and I don't have a good solution to >>>>>>> it. Since you're already cancelling all the active request anyway, what >>>>>>> do you think of always letting dwc3_gadget_ep_queue() to go through with >>>>>>> success, but report failure through request completion? >>>>>>> >>>>>> >>>>>> We do have something similar as well downstream (returning success >>>>>> always on dwc3_gadget_ep_queue()) and its been working for us also. >>>>>> Problem is we don't test the ISOC path much, so this is the only type of >>>>>> EP that might come into question... >>>>>> >>>>> >>>>> It should be similiar with isoc. I can't think of a potential issue yet. >>>>> >>>>>> Coming up with a way to address the concerns you brought up was a bit >>>>>> difficult as there were scenarios we needed to consider. next_request() >>>>>> doesn't always have to be the request being queued (even if ep queue >>>>>> triggered it). There was no easy way to determine if kick transfer was >>>>>> due to ep queue, but even if there was, we'd need to remember the >>>>>> previous point as well. >>>>>> >>>>> >>>>> Yeah, there are a few pitfalls. I don't have a good solution to it if we >>>>> want to return failure immediately and let the function driver handle >>>>> the dequeue (if it wants to). >>>>> >>>>> Thanks, >>>>> Thinh >>>>> >>>> >>> >> > -- The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project
