On Fri, 28 Jun 2019, Andrey Konovalov wrote: > On Fri, Jun 28, 2019 at 6:44 PM Andrey Konovalov <andreyknvl@xxxxxxxxxx> wrote: > > > > On Tue, Jun 18, 2019 at 3:53 PM Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: ... > > > > > Another question: do I understand correctly, that we only proceed with > > > > > submitting an URB to get the data for the control OUT request > > > > > (ctrl->bRequestType doesn't have the USB_DIR_IN bit set) if > > > > > ctrl->wLength != 0? > > > > > > That's right. If a control-OUT transfer has wLength == 0, it means > > > there is no data stage. (And control-IN transfers are not allowed to > > > have wLength == 0.) > > > > And another one to clarify :) > > > > So if we got a setup() callback, which denotes: > > 1. an IN transfer, we need to submit an URB with response (even if > > wLength == 0). When it completes, the transaction is over, and we will > > get the next setup() callback (if there's going to be any). Yes, except that wLength should never be 0 for an IN transfer. If it is, it's a bug in the host. > > 2. an OUT transfer, we need to submit an URB to fetch the data (even > > if wLength == 0). > > Or more like: to fetch the data when wLength != 0 and to acknowledge > the request when wLength == 0. > > > When it completes, the transaction is over, and we > > will get the next setup() callback (if there's going to be any). > > > > Is the above correct? Correct. There has been some discussion (and a few patches posted) about modifying this approach. But for now, this is the way to do it. Alan Stern
