On Mon, 14 Jan 2019, Paul Elder wrote: > > > > Can you check your uvc > > > > changes using dummy_hcd with the patch below? > > > > > > I'm not sure what to make of the test results. I get the same results > > > with or without the patch. Which I guess makes sense... in dummy_queue, > > > this is getting hit when the uvc function driver tries to complete the > > > delayed status: > > > > > > req = usb_request_to_dummy_request(_req); > > > if (!_req || !list_empty(&req->queue) || !_req->complete) > > > return -EINVAL; > > > > > > So the delayed/explicit status stage is never completed, afaict. > > > > I presume you are hitting the !list_empty(&req->queue) test, yes? The > > other two tests are trivial. > > Yes, that is what's happening. > > > Triggering the !list_empty() test means the request has already been > > submitted and not yet completed. This probably indicates there is a > > bug in the uvc function driver code. > > The uvc function driver works with musb, though :/ > > I compared the sequence of calls to the uvc setup, completion handler, > and status stage sending, and for some reason dummy_hcd, after an OUT > setup-completion-status sequence, calls a completion-status-completion > sequence, and then goes on the the next request. musb simply goes on to > the next request after the setup-completion-status sequence. I don't quite understand. There's a control-OUT transfer, the setup, data, and status transactions all complete normally, and then what happens? What do you mean by "a completion-status-completion sequence"? A more detailed description would help. > I commented out the paranoia block in dummy_timer, and dummy_hcd still > does the extra completion, but it doesn't error out anymore. I doubt > that's the/a solution though, especially since I get: > > [ 22.616577] uvcvideo: Failed to query (129) UVC probe control : -75 (exp. 26). > [ 22.624481] uvcvideo: Failed to initialize the device (-5). > > Not sure if that's a result of dummy_hcd not supporting isochronous > transfers or not. > > I'm not sure where to continue investigating :/ Perhaps removing the "#if 0" protecting the dev_dbg line in dummy_queue() would provide some helpful output. Another thing to check would be if the "implement an emulated single-request FIFO" in dummy_queue() is causing trouble. There's no harm in replacing the long "if" condition with "if (0)". Alan Stern
