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

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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>
This commit is contained in:
Dan Streetman 2009-04-21 13:37:12 -04:00 committed by Greg Kroah-Hartman
parent 37768adf9a
commit c065c60e83
1 changed files with 1 additions and 1 deletions
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2
drivers/usb/host/ehci-sched.c
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@ -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]) {