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Subject[ 003/127] USB: fix latency in uhci-hcd and ohci-hcd
Date
3.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Alan Stern <stern@rowland.harvard.edu>

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@rowland.harvard.edu>
Reported-and-tested-by: Joe Rayhawk <jrayhawk@fairlystable.org>
CC: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/usb/host/ohci-hcd.c | 2 +-
drivers/usb/host/uhci-q.c | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)

--- 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? */
--- a/drivers/usb/host/uhci-q.c
+++ b/drivers/usb/host/uhci-q.c
@@ -1287,7 +1287,7 @@ static int uhci_submit_isochronous(struc
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)) {



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