On 01.07.2015 13:13, SAUROV KANTI SHYAM wrote:
> When a transfer is in progress and a STOP command is issued to xHC,
> xHC will generate 2 event TRBs on event ring:
> (1) Force Stopped Event TRB on successful completion of STOP cmd.
> (2) Transfer Event TRB for the TD which was in progress and
> stopped in the middle (with its Completion Code set to Stopped).
> Since the value of event->buffer is undefined and should be ignored,
> at this point the code should return after incrementing the dequeue
> pointer of event ring.
>
The first event should be a "stop, invalid length" transfer event in case we stop
in between TD's.
The event-> buffer should be valid and contain the current dequeue pointer value
of the ring, see xhci 1.0 section 4.6.9.
It might still be part of the previous TD, but this is is already taken care of in handle_tx_event():
/*
* Skip the Force Stopped Event. The event_trb(event_dma) of FSE
* is not in the current TD pointed by ep_ring->dequeue because
* that the hardware dequeue pointer still at the previous TRB
* of the current TD. The previous TRB maybe a Link TD or the
* last TRB of the previous TD. The command completion handle
* will take care the rest.
*/
if (!event_seg && (trb_comp_code == COMP_STOP ||
trb_comp_code == COMP_STOP_INVAL)) {
ret = 0;
goto cleanup;
}
The "stop,-invalid length" transfer event is followed by a command completion event, which
we handle by calling xhci_handle_cmd_stop_ep(), so no point in calling it from handle_tx_event()
Does this patch solve any issue in your case? there might be something else going on.
If you have some custom solution using event data TRBs on the transfer ring then it is
possible that it stops on an event data TRB, and the event->buffer is not a pointer to the ring.
In that case the ED (Event Data) bit in the transfer event should first be checked.
-Mathias
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