Hi,

Baolin Wang [off-list ref] writes:

quoted

quoted

quoted

quoted

quoted

quoted

quoted

quoted

 void dwc3_gadget_exit(struct dwc3 *dwc)
 {
+  int epnum;
+  unsigned long flags;
+
+  spin_lock_irqsave(&dwc->lock, flags);
+  for (epnum = 2; epnum < DWC3_ENDPOINTS_NUM; epnum++) {
+          struct dwc3_ep  *dep = dwc->eps[epnum];
+
+          if (!dep)
+                  continue;
+
+          dep->flags &= ~DWC3_EP_END_TRANSFER_PENDING;
+  }
+  spin_unlock_irqrestore(&dwc->lock, flags);
+
   usb_del_gadget_udc(&dwc->gadget);
   dwc3_gadget_free_endpoints(dwc);

free endpoints is a better place for this. It's already going to free
the memory anyway. Might as well clear all flags to 0 there.

But it won't solve the deadlock issue. Since dwc3_gadget_free_endpoints()
is called after usb_del_gadget_udc() and the deadlock happens when

usb_del_gadget_udc()->udc_stop()->dwc3_gadget_stop()->wait_event_lock_irq()

and DWC3_EP_END_TRANSFER_PENDING flag is set.

indeed. Iterating twice over the entire endpoint list seems
wasteful. Perhaps we just shouldn't wait when removing the UDC since
that's essentially what this patch will do, right? If you clear the flag
before calling ->udc_stop(), this means the loop in dwc3_gadget_stop()
will do nothing. Might as well remove it.

This means that we will never wait for DWC3_EP_END_TRANSFER_PENDING to clear
in dwc3_gadget_stop() like we used to. This is perfectly fine, right?

It makes sense to me as dwc3_gadget_stop() calls __dwc3_gadget_stop() which
masks all interrupts and nobody will ever clear that flag if it was set.

I don't think so. It can not mask the endpoint events, please check
the events which will be masked in DEVTEN register. The reason why we
should wait for DWC3_EP_END_TRANSFER_PENDING to clear is that,
sometimes the DWC3_DEPEVT_EPCMDCMPLT event will be triggered later
than 100us, but now we may have freed the gadget irq which will cause
crash.

We could mask command complete events as soon as ->udc_stop() is called,
right? Hmm, actually, __dwc3_gadget_stop() already clears DEVTEN
completely.

But which bit in DEVTEN says Endpoint events are disabled?

When we set up the DWC3_DEPCMD_ENDTRANSFER command in
dwc3_stop_active_transfer(), we can do not set DWC3_DEPCMD_CMDIOC,
then there will no endpoint command complete interrupts I think.

cmd |= DWC3_DEPCMD_CMDIOC;

I remember some part of the databook mandating CMDIOC to be set. We
could test it out without and see if anything blows up. I would,
however, require a lengthy comment explaining that we're deviating from
databook revision x.yya, section foobar because $reasons. :-)