Re: [PATCH v2 1/1] usb: xhci: fix checking ep busy for CFC

From: Sergei Shtylyov
Date: Thu Oct 29 2015 - 08:52:30 EST


On 10/29/2015 5:46 AM, Lu Baolu wrote:

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@xxxxxxxxxxxxxx>
Signed-off-by: Lu Baolu <>

Implement the logic in xhci_queue_isoc_tx_prepare() instead of
a seperated function as suggested by Mathias.

drivers/usb/host/xhci-ring.c | 32 ++++++--------------------------
1 file changed, 6 insertions(+), 26 deletions(-)

diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
index fa83625..8edc286 100644
--- a/drivers/usb/host/xhci-ring.c
+++ b/drivers/usb/host/xhci-ring.c
@@ -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)) {
+ if ((le32_to_cpu(ep_ctx->ep_info) & EP_STATE_MASK)
+ !list_empty(&ep_ring->td_list))
+ urb->start_frame = xep->next_frame_id;
+ goto skip_start_over;

Forgot {}?


start_frame = readl(&xhci->run_regs->microframe_index);

MBR, Sergei

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