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USB: revert periodic scheduling bugfix

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commit fdc03438f5 upstream.

This patch reverts commit 3e619d0415
(USB: EHCI: fix bug in scheduling periodic split transfers).  The
commit was valid -- it fixed a real bug -- but the periodic scheduler
in ehci-hcd is in such bad shape (especially the part that handles
split transactions) that fixing one bug is very likely to cause
another to surface.  That's what happened in this case; the result was
choppy and noisy playback on certain 24-bit audio devices.

The only real fix will be to rewrite this entire section of code.  My
next project...

This fixes https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1136110.

Thanks to Tim Richardson for extra testing and feedback, and to Joseph
Salisbury and Tyson Tan for tracking down the original source of the
problem.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
CC: Joseph Salisbury <joseph.salisbury@canonical.com>
CC: Tim Richardson <tim@tim-richardson.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
This commit is contained in:
Alan Stern 2013-05-28 14:03:10 -04:00 committed by Ben Hutchings
parent 5b9ce8be32
commit f35b59d2c1
1 changed files with 1 additions and 1 deletions
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2
drivers/usb/host/ehci-sched.c
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@ -236,7 +236,7 @@ static inline unsigned char tt_start_uframe(struct ehci_hcd *ehci, __hc32 mask)
}
static const unsigned char
max_tt_usecs[] = { 125, 125, 125, 125, 125, 125, 125, 25 };
max_tt_usecs[] = { 125, 125, 125, 125, 125, 125, 30, 0 };
/* carryover low/fullspeed bandwidth that crosses uframe boundries */
static inline void carryover_tt_bandwidth(unsigned short tt_usecs[8])