USB: EHCI: fix HUB TT scheduling issue with iso transfer

commit 811c926c538f7e8d3c08b630dd5844efd7e000f6 upstream.

The current TT scheduling doesn't allow to play and then record on a
full-speed device connected to a high speed hub.

The IN iso stream can only start on the first uframe (0-2 for a 165 us)
because of CSPLIT transactions.
For the OUT iso stream there no such restriction. uframe 0-5 are possible.

The idea of this patch is that the first uframe are precious (for IN TT iso
stream) and we should allocate the last uframes first if possible.

For that we reverse the order of uframe allocation (last uframe first).

Here an example :

hid interrupt stream
----------------------------------------------------------------------
uframe                |  0  |  1  |  2  |  3  |  4  |  5  |  6  |  7  |
----------------------------------------------------------------------
max_tt_usecs          | 125 | 125 | 125 | 125 | 125 | 125 | 30  |  0  |
----------------------------------------------------------------------
used usecs on a frame | 13  |  0  |  0  |  0  |  0  |  0  |  0  |  0  |
----------------------------------------------------------------------

iso OUT stream
----------------------------------------------------------------------
uframe                |  0  |  1  |  2  |  3  |  4  |  5  |  6  |  7  |
----------------------------------------------------------------------
max_tt_usecs          | 125 | 125 | 125 | 125 | 125 | 125 | 30  |  0  |
----------------------------------------------------------------------
used usecs on a frame | 13  | 125 |  39 |  0  |  0  |  0  |  0  |  0  |
----------------------------------------------------------------------

There no place for iso IN stream  (uframe 0-2 are used) and we got "cannot
submit datapipe for urb 0, error -28: not enough bandwidth" error.

With the patch this become.

iso OUT stream
----------------------------------------------------------------------
uframe                |  0  |  1  |  2  |  3  |  4  |  5  |  6  |  7  |
----------------------------------------------------------------------
max_tt_usecs          | 125 | 125 | 125 | 125 | 125 | 125 | 30  |  0  |
----------------------------------------------------------------------
used usecs on a frame |  13 |  0  |  0  |  0  | 125 |  39 |  0  |  0  |
----------------------------------------------------------------------

iso IN stream
----------------------------------------------------------------------
uframe                |  0  |  1  |  2  |  3  |  4  |  5  |  6  |  7  |
----------------------------------------------------------------------
max_tt_usecs          | 125 | 125 | 125 | 125 | 125 | 125 | 30  |  0  |
----------------------------------------------------------------------
used usecs on a frame |  13 |  0  | 125 | 40  | 125 |  39 |  0  |  0  |
----------------------------------------------------------------------

Signed-off-by: Matthieu Castet <matthieu.castet@parrot.com>
Signed-off-by: Thomas Poussevin <thomas.poussevin@parrot.com>
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/drivers/usb/host/ehci-sched.c b/drivers/usb/host/ehci-sched.c
index 29bec34973b943800b193a3059a10c3c0ff008d3..afef3df9757d4fbb40231cc96fc1956bbb3e7af8 100644 (file)
--- a/drivers/usb/host/ehci-sched.c
+++ b/drivers/usb/host/ehci-sched.c
@@ -1480,10 +1480,15 @@ iso_stream_schedule (
 
                /* NOTE:  assumes URB_ISO_ASAP, to limit complexity/bugs */
 
-               /* find a uframe slot with enough bandwidth */
-               next = start + period;
-               for (; start < next; start++) {
-
+               /* find a uframe slot with enough bandwidth.
+                * Early uframes are more precious because full-speed
+                * iso IN transfers can't use late uframes,
+                * and therefore they should be allocated last.
+                */
+               next = start;
+               start += period;
+               do {
+                       start--;
                        /* check schedule: enough space? */
                        if (stream->highspeed) {
                                if (itd_slot_ok(ehci, mod, start,
@@ -1496,7 +1501,7 @@ iso_stream_schedule (
                                                start, sched, period))
                                        break;
                        }
-               }
+               } while (start > next);
 
                /* no room in the schedule */
                if (start == next) {