[PATCH 1/1] usb: xhci: fix checking ep busy for CFC

[Lu Baolu <baolu.lu@linux.intel.com>]

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: YD Tseng <yd_tseng@asmedia.com.tw>
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
---
 drivers/usb/host/xhci-ring.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
index fa83625..2b50d45 100644
--- a/drivers/usb/host/xhci-ring.c
+++ b/drivers/usb/host/xhci-ring.c
@@ -3903,7 +3903,6 @@ static int ep_ring_is_processing(struct xhci_hcd *xhci,
 	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];
@@ -3913,9 +3912,7 @@ static int ep_ring_is_processing(struct xhci_hcd *xhci,
 	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));
+	return !list_empty(&ep_ring->td_list);
 }
 
 /*
-- 
2.1.4