USB: UHCI: improve scheduling of interrupt URBs

This patch (as1140) adds a little intelligence to the interrupt-URB
scheduler in uhci-hcd.  Right now the scheduler is stupid; every URB
having the same period is assigned to the same slot.  Thus a large
group of period-N URBs can fill their slot and cause -ENOSPC errors
even when all the lower-period slots are empty.

With the patch, if an URB doesn't fit in its assigned slot then the
scheduler will try using lower-period slots.  This will provide
greater flexibility.  As an example, the driver will be able to handle
more than just three or four mice, which the current driver cannot.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 11 insertions, 6 deletions

diff --git a/drivers/usb/host/uhci-q.c b/drivers/usb/host/uhci-q.c
index 1f0c2cf26e5d..5631d89c8730 100644
--- a/drivers/usb/host/uhci-q.c
+++ b/drivers/usb/host/uhci-q.c
@@ -1065,13 +1065,18 @@ static int uhci_submit_interrupt(struct uhci_hcd *uhci, struct urb *urb,
                 }
                 if (exponent < 0)
                         return -EINVAL;
-                qh->period = 1 << exponent;
-                qh->skel = SKEL_INDEX(exponent);
 
-                /* For now, interrupt phase is fixed by the layout
-                 * of the QH lists. */
-                qh->phase = (qh->period / 2) & (MAX_PHASE - 1);
-                ret = uhci_check_bandwidth(uhci, qh);
+                /* If the slot is full, try a lower period */
+                do {
+                        qh->period = 1 << exponent;
+                        qh->skel = SKEL_INDEX(exponent);
+
+                        /* For now, interrupt phase is fixed by the layout
+                         * of the QH lists.
+                         */
+                        qh->phase = (qh->period / 2) & (MAX_PHASE - 1);
+                        ret = uhci_check_bandwidth(uhci, qh);
+                } while (ret != 0 && --exponent >= 0);
                 if (ret)
                         return ret;
         } else if (qh->period > urb->interval)