USB: EHCI: fix initialization bug in iso_stream_schedule()

commit 6d89252a upstream.

Commit c3ee9b76 (EHCI: improved logic for isochronous scheduling)
introduced the idea of using ehci->last_iso_frame as the origin (or
base) for the circular calculations involved in modifying the
isochronous schedule.  However, the new code it added used
ehci->last_iso_frame before the value was properly initialized.  This
patch rectifies the mistake by moving the initialization lines earlier
in iso_stream_schedule().

This fixes Bugzilla #72891.
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Fixes: c3ee9b76Reported-by: Joe Bryant <tenminjoe@yahoo.com>
Tested-by: Joe Bryant <tenminjoe@yahoo.com>
Tested-by: Martin Long <martin@longhome.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

drivers/usb/host/ehci-sched.c

@@ -1581,6 +1581,10 @@ iso_stream_schedule (
 	else
 		next = (now + 2 + 7) & ~0x07;	/* full frame cache */
 
+	/* If needed, initialize last_iso_frame so that this URB will be seen */
+	if (ehci->isoc_count == 0)
+		ehci->last_iso_frame = now >> 3;
+
 	/*
 	 * Use ehci->last_iso_frame as the base.  There can't be any
 	 * TDs scheduled for earlier than that.
@@ -1671,10 +1675,6 @@ iso_stream_schedule (
 	urb->start_frame = start & (mod - 1);
 	if (!stream->highspeed)
 		urb->start_frame >>= 3;
-
-	/* Make sure scan_isoc() sees these */
-	if (ehci->isoc_count == 0)
-		ehci->last_iso_frame = now >> 3;
 	return status;
 
  fail: