On Thu, Feb 02, 2023 at 10:12:45AM +0000, Dan Scally wrote: > (+CC roger as the author of the USB_GADGET_DELAYED_STATUS mechanism) > > On 26/01/2023 23:57, Thinh Nguyen wrote: > > We should already have this mechanism in place to do protocol STALL. > > Please look into delayed_status and set halt. > > > Thanks; I tried this by returning USB_GADGET_DELAYED_STATUS from the > function's .setup() callback and later (after userspace checks the data > packet) either calling usb_ep_queue() or usb_ep_set_halt() and it does seem > to be working. This surprises me, as my understanding was that the purpose > of USB_GADGET_DELAYED_STATUS is to pause all control transfers including > the data phase to give the function driver enough time to queue a request > (and possibly only for specific requests). Regardless though I think the > conclusion from previous discussions on this topic (see [1] for example) was > that we don't want to rely on USB_GADGET_DELAYED_STATUS to do this which is > why I had avoided it in the first place. A colleague made a series [2] some > time ago that adds a flag to usb_request which function drivers can set when > queuing the data phase request. UDC drivers then read that flag to decide > whether to delay the status phase until after another usb_ep_queue(), and > that's what I'm trying to implement here. > > > [1] https://lkml.org/lkml/2018/10/10/138 > > [2] https://patchwork.kernel.org/project/linux-usb/patch/20190124030228.19840-5-paul.elder@xxxxxxxxxxxxxxxx/ I'm in favor of the explicit_status approach from [2]. In fact, there was a whole series of patches impementing this, and I don't think any of them were merged. Keep in mind that there are two separate issues here: Status/data stage for a control-IN or 0-length control-OUT transfer. Status stage for a non-0-length control-OUT transfer. The USB_GADGET_DELAYED_STATUS mechanism was meant to help with the first, not the second. explicit_status was meant to help with the second; it may be able to help with both. Alan Stern
