Hi Mathias, Alan and all,
During xhci handling a completion event for stop endpoint command ,
xhci_handle_cmd_stop_ep() always gives back a urb with status set to 0.
The comment says,
/* Doesn't matter what we pass for status, since the
core will
* just overwrite it (because the URB has been unlinked).
*/
I don't think this assumption is always correct. Stop endpoint command
is used in below two cases in xhci driver.
1. In xhci_urb_dequeue(). This is the hcd driver interface for canceling
a transfer.
2. During suspend process. This is to stop on-going transfers and cause
xHC to save various endpoint state into memory.
The assumption of "URB has been unlinked" is only the fact for case 1.
It's wrong in case 2. If my understanding is right, USB client drivers
(serial, mass storage ....) might receive an incompletion urb transfer
with status set to success during suspend/resume.
Please correct me if there is any misunderstanding.
[below is the code segment in xhci_handle_cmd_stop_ep()]
/*
* Drop the lock and complete the URBs in the cancelled TD list.
* New TDs to be cancelled might be added to the end of the
list before
* we can complete all the URBs for the TDs we already unlinked.
* So stop when we've completed the URB for the last TD we
unlinked.
*/
do {
cur_td = list_entry(ep->cancelled_td_list.next,
struct xhci_td, cancelled_td_list);
list_del_init(&cur_td->cancelled_td_list);
/* Clean up the cancelled URB */
/* Doesn't matter what we pass for status, since the
core will
* just overwrite it (because the URB has been unlinked).
*/
xhci_giveback_urb_in_irq(xhci, cur_td, 0);
/* Stop processing the cancelled list if the watchdog
timer is
* running.
*/
if (xhci->xhc_state & XHCI_STATE_DYING)
return;
} while (cur_td != last_unlinked_td);
[end of code segment]
Beset Regards,
Lu Baolu
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