2 files changed, 33 insertions, 39 deletions

diff --git a/drivers/usb/host/ehci-sched.c b/drivers/usb/host/ehci-sched.c
index 7cf3da7babf0..7eb242f27c00 100644
--- a/drivers/usb/host/ehci-sched.c
+++ b/drivers/usb/host/ehci-sched.c
@@ -1361,7 +1361,7 @@ sitd_slot_ok (
  * given EHCI_TUNE_FLS and the slop).  Or, write a smarter scheduler!
  */
 
-#define SCHEDULE_SLOP   80      /* microframes */
+#define SCHEDULING_DELAY        40      /* microframes */
 
 static int
 iso_stream_schedule (
@@ -1370,7 +1370,7 @@ iso_stream_schedule (
         struct ehci_iso_stream  *stream
 )
 {
-        u32                     now, next, start, period, span;
+        u32                     now, base, next, start, period, span;
         int                     status;
         unsigned                mod = ehci->periodic_size << 3;
         struct ehci_iso_sched   *sched = urb->hcpriv;
@@ -1382,12 +1382,6 @@ iso_stream_schedule (
                 span <<= 3;
         }
 
-        if (span > mod - SCHEDULE_SLOP) {
-                ehci_dbg (ehci, "iso request %p too long\n", urb);
-                status = -EFBIG;
-                goto fail;
-        }
-
         now = ehci_read_frame_index(ehci) & (mod - 1);
 
         /* Typical case: reuse current schedule, stream is still active.
@@ -1396,7 +1390,6 @@ iso_stream_schedule (
          * slot in the schedule, implicitly assuming URB_ISO_ASAP.
          */
         if (likely (!list_empty (&stream->td_list))) {
-                u32     excess;
 
                 /* For high speed devices, allow scheduling within the
                  * isochronous scheduling threshold.  For full speed devices
@@ -1408,36 +1401,41 @@ iso_stream_schedule (
                 else
                         next = now;
 
-                /* Fell behind (by up to twice the slop amount)?
-                 * We decide based on the time of the last currently-scheduled
-                 * slot, not the time of the next available slot.
+                /*
+                 * Use ehci->last_iso_frame as the base.  There can't be any
+                 * TDs scheduled for earlier than that.
                  */
-                excess = (stream->next_uframe - period - next) & (mod - 1);
-                if (excess >= mod - 2 * SCHEDULE_SLOP)
-                        start = next + excess - mod + period *
-                                        DIV_ROUND_UP(mod - excess, period);
-                else
-                        start = next + excess + period;
-                if (start - now >= mod) {
-                        ehci_dbg(ehci, "request %p would overflow (%d+%d >= %d)\n",
-                                        urb, start - now - period, period,
-                                        mod);
-                        status = -EFBIG;
+                base = ehci->last_iso_frame << 3;
+                next = (next - base) & (mod - 1);
+                start = (stream->next_uframe - base) & (mod - 1);
+
+                /* Is the schedule already full? */
+                if (unlikely(start < period)) {
+                        ehci_dbg(ehci, "iso sched full %p (%u-%u < %u mod %u)\n",
+                                        urb, stream->next_uframe, base,
+                                        period, mod);
+                        status = -ENOSPC;
                         goto fail;
                 }
+
+                /* Behind the scheduling threshold?  Assume URB_ISO_ASAP. */
+                if (unlikely(start < next))
+                        start += period * DIV_ROUND_UP(next - start, period);
+
+                start += base;
         }
 
         /* need to schedule; when's the next (u)frame we could start?
          * this is bigger than ehci->i_thresh allows; scheduling itself
-         * isn't free, the slop should handle reasonably slow cpus.  it
+         * isn't free, the delay should handle reasonably slow cpus.  it
          * can also help high bandwidth if the dma and irq loads don't
          * jump until after the queue is primed.
          */
         else {
                 int done = 0;
-                start = SCHEDULE_SLOP + (now & ~0x07);
 
-                /* NOTE:  assumes URB_ISO_ASAP, to limit complexity/bugs */
+                base = now & ~0x07;
+                start = base + SCHEDULING_DELAY;
 
                 /* find a uframe slot with enough bandwidth.
                  * Early uframes are more precious because full-speed
@@ -1464,19 +1462,16 @@ iso_stream_schedule (
 
                 /* no room in the schedule */
                 if (!done) {
-                        ehci_dbg(ehci, "iso resched full %p (now %d max %d)\n",
-                                urb, now, now + mod);
+                        ehci_dbg(ehci, "iso sched full %p", urb);
                         status = -ENOSPC;
                         goto fail;
                 }
         }
 
         /* Tried to schedule too far into the future? */
-        if (unlikely(start - now + span - period
-                                >= mod - 2 * SCHEDULE_SLOP)) {
-                ehci_dbg(ehci, "request %p would overflow (%d+%d >= %d)\n",
-                                urb, start - now, span - period,
-                                mod - 2 * SCHEDULE_SLOP);
+        if (unlikely(start - base + span - period >= mod)) {
+                ehci_dbg(ehci, "request %p would overflow (%u+%u >= %u)\n",
+                                urb, start - base, span - period, mod);
                 status = -EFBIG;
                 goto fail;
         }
@@ -1490,7 +1485,7 @@ iso_stream_schedule (
 
         /* Make sure scan_isoc() sees these */
         if (ehci->isoc_count == 0)
-                ehci->next_frame = now >> 3;
+                ehci->last_iso_frame = now >> 3;
         return 0;
 
  fail:
@@ -2220,16 +2215,16 @@ static void scan_isoc(struct ehci_hcd *ehci)
                 now_frame = (uf >> 3) & fmask;
                 live = true;
         } else  {
-                now_frame = (ehci->next_frame - 1) & fmask;
+                now_frame = (ehci->last_iso_frame - 1) & fmask;
                 live = false;
         }
         ehci->now_frame = now_frame;
 
-        frame = ehci->next_frame;
         for (;;) {
                 union ehci_shadow       q, *q_p;
                 __hc32                  type, *hw_p;
 
+                frame = ehci->last_iso_frame;
 restart:
                 /* scan each element in frame's queue for completions */
                 q_p = &ehci->pshadow [frame];
@@ -2334,7 +2329,6 @@ restart:
                 /* Stop when we have reached the current frame */
                 if (frame == now_frame)
                         break;
-                frame = (frame + 1) & fmask;
+                ehci->last_iso_frame = (frame + 1) & fmask;
         }
-        ehci->next_frame = now_frame;
 }
diff --git a/drivers/usb/host/ehci.h b/drivers/usb/host/ehci.h
index da07d98f7d1d..0564a63f5eb3 100644
--- a/drivers/usb/host/ehci.h
+++ b/drivers/usb/host/ehci.h
@@ -143,7 +143,7 @@ struct ehci_hcd {			/* one per controller */
         struct ehci_qh          *intr_unlink_last;
         unsigned                intr_unlink_cycle;
         unsigned                now_frame;      /* frame from HC hardware */
-        unsigned                next_frame;     /* scan periodic, start here */
+        unsigned                last_iso_frame; /* last frame scanned for iso */
         unsigned                intr_count;     /* intr activity count */
         unsigned                isoc_count;     /* isoc activity count */
         unsigned                periodic_count; /* periodic activity count */