[ 3.8.y.z extended stable ] Patch "USB: fix latency in uhci-hcd and ohci-hcd" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    USB: fix latency in uhci-hcd and ohci-hcd

to the linux-3.8.y-queue branch of the 3.8.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.8.y-queue

This patch is scheduled to be released in version 3.8.13.2.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.8.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 6e0f1ddb3d124e3e062ddadf9f2e0433d6c94a3b Mon Sep 17 00:00:00 2001
From: Alan Stern <stern at rowland.harvard.edu>
Date: Tue, 14 May 2013 13:57:19 -0400
Subject: USB: fix latency in uhci-hcd and ohci-hcd

commit e1944017839d7dfbf7329fac4bdec8b4050edf5e upstream.

Commits c44b225077bb1fb25ed5cd5c4f226897b91bedd4 (UHCI: implement new
semantics for URB_ISO_ASAP) and
6a41b4d3fe8cd4cc95181516fc6fba7b1747a27c (OHCI: implement new
semantics for URB_ISO_ASAP) increased the latency for isochronous URBs
in uhci-hcd and ohci-hcd respectively to 2 milliseconds, in an
attempt to avoid underruns.  It turns out that not only was this
unnecessary -- 1-ms latency works okay -- it also causes problems with
certain application loads such as real-time audio.

This patch changes the latency for both drivers back to 1 ms.

This should be applied to -stable kernels going back to 3.8.

Signed-off-by: Alan Stern <stern at rowland.harvard.edu>
Reported-and-tested-by: Joe Rayhawk <jrayhawk at fairlystable.org>
CC: Clemens Ladisch <clemens at ladisch.de>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/usb/host/ohci-hcd.c | 2 +-
 drivers/usb/host/uhci-q.c   | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/host/ohci-hcd.c b/drivers/usb/host/ohci-hcd.c
index 180a2b0..4b6d1c8 100644
--- a/drivers/usb/host/ohci-hcd.c
+++ b/drivers/usb/host/ohci-hcd.c
@@ -233,7 +233,7 @@ static int ohci_urb_enqueue (
 			urb->start_frame = frame;
 		}
 	} else if (ed->type == PIPE_ISOCHRONOUS) {
-		u16	next = ohci_frame_no(ohci) + 2;
+		u16	next = ohci_frame_no(ohci) + 1;
 		u16	frame = ed->last_iso + ed->interval;

 		/* Behind the scheduling threshold? */
diff --git a/drivers/usb/host/uhci-q.c b/drivers/usb/host/uhci-q.c
index 15921fd..3b08519 100644
--- a/drivers/usb/host/uhci-q.c
+++ b/drivers/usb/host/uhci-q.c
@@ -1287,7 +1287,7 @@ static int uhci_submit_isochronous(struct uhci_hcd *uhci, struct urb *urb,
 		return -EINVAL;		/* Can't change the period */

 	} else {
-		next = uhci->frame_number + 2;
+		next = uhci->frame_number + 1;

 		/* Find the next unused frame */
 		if (list_empty(&qh->queue)) {
--
1.8.1.2