USB: ehci-sched.c: EHCI SITD scheduling bugfix

Without this patch, the driver won't check that the last fully-occupied
uframe for a new split transaction was vacant beforehand.  This can
lead to a situation in which the first 188 bytes of a 192-byte
isochronous transfer are scheduled in the same uframe as an existing
interrupt transfer.  The resulting schedule looks like this:

       uframe 0: 188-byte isoc-OUT SSPLIT, 8-byte int-IN SSPLIT
       uframe 1: 4-byte isoc-OUT SSPLIT

The SSPLITs are intermingled, causing an error in the downstream hub's
TT.

If you are having problems with devices or hub ports resetting, or failed
interrupt transfers, when you start using a USB audio or video (Isochronous)
device, this patch may help.

Signed-off-by: Dan Streetman <ddstreet@ieee.org>
Reported-by: Kung James <kong1191@gmail.com>
Acked-by: David Brownell <dbrownell@users.sourceforge.net>
Cc: Alan Stern <stern@rowland.harvard.edu>

diff --git a/drivers/usb/host/ehci-sched.c b/drivers/usb/host/ehci-sched.c
index ada5d2ba297be1353bf60a8f1c5dc3d5199078df..556d0ec0c1f81048044a7b6e51019a5a1d4443e5 100644 (file)
--- a/drivers/usb/host/ehci-sched.c
+++ b/drivers/usb/host/ehci-sched.c
@@ -323,7 +323,7 @@ static int tt_available (
                 * already scheduled transactions
                 */
                if (125 < usecs) {
-                       int ufs = (usecs / 125) - 1;
+                       int ufs = (usecs / 125);
                        int i;
                        for (i = uframe; i < (uframe + ufs) && i < 8; i++)
                                if (0 < tt_usecs[i]) {