On Thu, Jan 10, 2019 at 03:39:25PM -0500, Alan Stern wrote: > On Wed, 9 Jan 2019, Paul Elder wrote: > > > This patch series adds a mechanism to allow asynchronously validating > > the data stage of a control OUT request, and for stalling or suceeding > > the request accordingly. > > One thing we haven't mentioned explicitly: What should happen when the > time for the status stage rolls around if the gadget driver queues a > non-zero length request? Ah, yeah, I missed that. > This can happen in a few different ways. One obvious possibility is > that the gadget driver sets the explicit_status flag and then submits a > non-zero length request. Another is that the gadget driver submits > _two_ requests during the data stage (the second would be interpreted > as the status-stage request). A third is that the gadget driver > submits a data-stage request that is too long and the excess portion is > used for the status stage. > > My feeling is that the behavior in these cases should officially be > undefined. Almost anything could happen: the status stage could STALL, > it could succeed, it could NAK, or it could send a non-zero packet to > the host. The request could return with 0 status or an error status, > and req->actual could take on any reasonable value. > > Alternatively, the UDC driver could detect these errors and report them > somehow. Maybe STALL the status stage and complete the request with > -EPIPE status or some such thing. > > Any preferences or other ideas? I think error detection and reporting would be useful. The question is what action to take after that; either leave it undefined or STALL. I think STALL would be fine, since if a non-zero length request is submitted for a status stage, intentionally or not, it isn't part of proper behavior and should count as an error. > One other thing: Some UDC drivers may assume that the data stage of a > control transfer never spans more than a single usb_request. Should > this become an official requirement? Would the data stage of a control transfer ever need more space than a single usb_request can contain? I know UVC doesn't; that's why we pack it together with the setup stage data in 3/6. If so, I would think we can make it a requirement. Paul
