diff options
authorAlan Stern <>2009-11-18 11:37:15 -0500
committerGreg Kroah-Hartman <>2009-12-08 10:22:12 -0800
commit3d57f55a87be678c0e3a91842a3ca2ca4ffcdcaf (patch)
parent7eeea230e8e078b125436e796cf30b71098107b7 (diff)
USB: EHCI: don't send Clear-TT-Buffer following a STALL
commit c2f6595fbdb408d3d6850cfae590c8fa93e27399 upstream. This patch (as1304) fixes a regression in ehci-hcd. Evidently some hubs don't handle Clear-TT-Buffer requests correctly, so we should avoid sending them when they don't appear to be absolutely necessary. The reported symptom is that output on a downstream audio device cuts out because the hub stops relaying isochronous packets. The patch prevents Clear-TT-Buffer requests from being sent following a STALL handshake. In theory a STALL indicates either that the downstream device sent a STALL or that no matching TT buffer could be found. In either case, the transfer is completed and the TT buffer does not remain busy, so it doesn't need to be cleared. Also, the patch fixes a minor flaw in the code that actually sends the Clear-TT-Buffer requests. Although the pipe direction isn't really used for control transfers, it should be a Send rather than a Receive. Signed-off-by: Alan Stern <> Reported-by: Javier Kohen <> CC: David Brownell <> Signed-off-by: Greg Kroah-Hartman <>
2 files changed, 15 insertions, 3 deletions
diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
index 71f86c60d83c..b41989e0c6c1 100644
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -439,7 +439,7 @@ resubmit:
static inline int
hub_clear_tt_buffer (struct usb_device *hdev, u16 devinfo, u16 tt)
- return usb_control_msg(hdev, usb_rcvctrlpipe(hdev, 0),
+ return usb_control_msg(hdev, usb_sndctrlpipe(hdev, 0),
tt, NULL, 0, 1000);
diff --git a/drivers/usb/host/ehci-q.c b/drivers/usb/host/ehci-q.c
index 7673554fa64d..6b6c240cbe72 100644
--- a/drivers/usb/host/ehci-q.c
+++ b/drivers/usb/host/ehci-q.c
@@ -475,8 +475,20 @@ halt:
* we must clear the TT buffer (11.17.5).
if (unlikely(last_status != -EINPROGRESS &&
- last_status != -EREMOTEIO))
- ehci_clear_tt_buffer(ehci, qh, urb, token);
+ last_status != -EREMOTEIO)) {
+ /* The TT's in some hubs malfunction when they
+ * receive this request following a STALL (they
+ * stop sending isochronous packets). Since a
+ * STALL can't leave the TT buffer in a busy
+ * state (if you believe Figures 11-48 - 11-51
+ * in the USB 2.0 spec), we won't clear the TT
+ * buffer in this case. Strictly speaking this
+ * is a violation of the spec.
+ */
+ if (last_status != -EPIPE)
+ ehci_clear_tt_buffer(ehci, qh, urb,
+ token);
+ }
/* if we're removing something not at the queue head,