xhci: dbc: Don't use generic xhci inc_deq() function for dbc

The generic inc_deq() helper takes struct xhci_hcd pointer as a parameter,
and is a lot more complex than needed for the DbC usecase.

In order to decouple xhci and DbC we have to create our own small
inc_evt_deq() helper, not relying on xhci.
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://lore.kernel.org/r/20200723144530.9992-3-mathias.nyman@linux.intel.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/host/xhci-dbgcap.c

@@ -644,6 +644,17 @@ static void dbc_handle_xfer_event(struct xhci_hcd *xhci, union xhci_trb *event)
 	xhci_dbc_giveback(req, status);
 }
 
+static void inc_evt_deq(struct xhci_ring *ring)
+{
+	/* If on the last TRB of the segment go back to the beginning */
+	if (ring->dequeue == &ring->deq_seg->trbs[TRBS_PER_SEGMENT - 1]) {
+		ring->cycle_state ^= 1;
+		ring->dequeue = ring->deq_seg->trbs;
+		return;
+	}
+	ring->dequeue++;
+}
+
 static enum evtreturn xhci_dbc_do_handle_events(struct xhci_dbc *dbc)
 {
 	dma_addr_t		deq;
@@ -765,7 +776,8 @@ static enum evtreturn xhci_dbc_do_handle_events(struct xhci_dbc *dbc)
 			break;
 		}
 
-		inc_deq(xhci, dbc->ring_evt);
+		inc_evt_deq(dbc->ring_evt);
+
 		evt = dbc->ring_evt->dequeue;
 		update_erdp = true;
 	}