git » linux-kernel » commit c2f6595

USB: EHCI: don't send Clear-TT-Buffer following a STALL

author Alan Stern
2009-11-18 16:37:15 UTC
committer Greg Kroah-Hartman
2009-12-01 00:43:15 UTC
parent a8a84540eb3fd0493f250dc1c513bef6810a50fd
USB: EHCI: don't send Clear-TT-Buffer following a STALL

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 <stern@rowland.harvard.edu>
Reported-by: Javier Kohen <jkohen@users.sourceforge.net>
CC: David Brownell <david-b@pacbell.net>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
drivers/usb/core/hub.c +1 -1
drivers/usb/host/ehci-q.c +14 -2 
diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
index 5ce839137ad..0f857e64505 100644
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -444,7 +444,7 @@ 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),
 			       HUB_CLEAR_TT_BUFFER, USB_RT_PORT, devinfo,
 			       tt, NULL, 0, 1000);
 }
diff --git a/drivers/usb/host/ehci-q.c b/drivers/usb/host/ehci-q.c
index 00ad9ce392e..139a2cc3f64 100644
--- a/drivers/usb/host/ehci-q.c
+++ b/drivers/usb/host/ehci-q.c
@@ -487,8 +487,20 @@ 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,