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SubjectRe: usb/gadget: stalls in dummy_timer
On Thu, 14 Sep 2017, Andrey Konovalov wrote:

> Looked at this a little more.
>
> dummy_timer() stucks in an infinite loop. It calls
> usb_hcd_giveback_urb(), which in turn calls usbtouch_irq(), which
> calls usb_submit_urb(), which calls dummy_urb_enqueue() and puts urb
> back into dummy urb queue. dummy_timer() then does goto restart, finds
> the urb and calls usb_hcd_giveback_urb() again. And this process goes
> on again and again. It seems that something should either process the
> urb and set urb->status or it should just expire.

There is some throttling code, but it applies only to bulk transfers.
Probably because the bandwidth limits for other types are slightly
different. However, I don't think we need to worry about this level of
detail, since the driver makes a number of other approximations anyway.

Try the patch below; it should fix the problem.

Alan Stern



Index: usb-4.x/drivers/usb/gadget/udc/dummy_hcd.c
===================================================================
--- usb-4.x.orig/drivers/usb/gadget/udc/dummy_hcd.c
+++ usb-4.x/drivers/usb/gadget/udc/dummy_hcd.c
@@ -1781,7 +1781,6 @@ restart:
struct dummy_request *req;
u8 address;
struct dummy_ep *ep = NULL;
- int type;
int status = -EINPROGRESS;

urb = urbp->urb;
@@ -1789,14 +1788,10 @@ restart:
goto return_urb;
else if (dum_hcd->rh_state != DUMMY_RH_RUNNING)
continue;
- type = usb_pipetype(urb->pipe);

- /* used up this frame's non-periodic bandwidth?
- * FIXME there's infinite bandwidth for control and
- * periodic transfers ... unrealistic.
- */
- if (total <= 0 && type == PIPE_BULK)
- continue;
+ /* Used up this frame's bandwidth? */
+ if (total <= 0)
+ break;

/* find the gadget's ep for this request (if configured) */
address = usb_pipeendpoint (urb->pipe);
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