On 02/02/2023 14:52, Alan Stern wrote:
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.
Yep, I'm picking that series up and want to get it 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.
Ack - thanks. That thread I linked was very informative, I wish I'd
found it sooner!
Alan Stern
