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

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>
CC: <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/usb/host/ohci-hcd.c b/drivers/usb/host/ohci-hcd.c
index 9e6de9586ae4bf82afb01f4c70464ffbbcd01117..df1af0bcfe994968000b289b5ce4148095914130 100644 (file)
--- 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 f0976d8190bc363b52d908540de8214fbeed43b8..041c6ddb695c8ec6fa17d371fe7904de2e47d5ab 100644 (file)
--- 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)) {