usb: xhci: fix checking ep busy for CFC

Function ep_ring_is_processing() checks the dequeue pointer
in endpoint context to know whether an endpoint is busy with
processing TRBs. This is not correct since dequeue pointer
field in an endpoint context is only valid when the endpoint
is in Halted or Stopped states. This buggy code causes audio
noise when playing sound with USB headset connected to host
controllers which support CFC (one of xhci 1.1 features).

This patch should exist in stable kernel since v4.3.
Reported-and-tested-by: NYD Tseng <yd_tseng@asmedia.com.tw>
Signed-off-by: NLu Baolu <baolu.lu@linux.intel.com>
Cc: stable <stable@vger.kernel.org> # v4.3
Signed-off-by: NMathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/host/xhci-ring.c

@@ -3896,28 +3896,6 @@ static int xhci_queue_isoc_tx(struct xhci_hcd *xhci, gfp_t mem_flags,
 	return ret;
 }
 
-static int ep_ring_is_processing(struct xhci_hcd *xhci,
-		int slot_id, unsigned int ep_index)
-{
-	struct xhci_virt_device *xdev;
-	struct xhci_ring *ep_ring;
-	struct xhci_ep_ctx *ep_ctx;
-	struct xhci_virt_ep *xep;
-	dma_addr_t hw_deq;
-
-	xdev = xhci->devs[slot_id];
-	xep = &xhci->devs[slot_id]->eps[ep_index];
-	ep_ring = xep->ring;
-	ep_ctx = xhci_get_ep_ctx(xhci, xdev->out_ctx, ep_index);
-
-	if ((le32_to_cpu(ep_ctx->ep_info) & EP_STATE_MASK) != EP_STATE_RUNNING)
-		return 0;
-
-	hw_deq = le64_to_cpu(ep_ctx->deq) & ~EP_CTX_CYCLE_MASK;
-	return (hw_deq !=
-		xhci_trb_virt_to_dma(ep_ring->enq_seg, ep_ring->enqueue));
-}
-
 /*
  * Check transfer ring to guarantee there is enough room for the urb.
  * Update ISO URB start_frame and interval.
@@ -3983,10 +3961,12 @@ int xhci_queue_isoc_tx_prepare(struct xhci_hcd *xhci, gfp_t mem_flags,
 	}
 
 	/* Calculate the start frame and put it in urb->start_frame. */
-	if (HCC_CFC(xhci->hcc_params) &&
-			ep_ring_is_processing(xhci, slot_id, ep_index)) {
-		urb->start_frame = xep->next_frame_id;
-		goto skip_start_over;
+	if (HCC_CFC(xhci->hcc_params) && !list_empty(&ep_ring->td_list)) {
+		if ((le32_to_cpu(ep_ctx->ep_info) & EP_STATE_MASK) ==
+				EP_STATE_RUNNING) {
+			urb->start_frame = xep->next_frame_id;
+			goto skip_start_over;
+		}
 	}
 
 	start_frame = readl(&xhci->run_regs->microframe_index);