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-rw-r--r--drivers/media/video/bt8xx/bttv-driver.c31
1 files changed, 27 insertions, 4 deletions
diff --git a/drivers/media/video/bt8xx/bttv-driver.c b/drivers/media/video/bt8xx/bttv-driver.c
index 939d1e51297..3ff84c8185a 100644
--- a/drivers/media/video/bt8xx/bttv-driver.c
+++ b/drivers/media/video/bt8xx/bttv-driver.c
@@ -3800,11 +3800,34 @@ bttv_irq_next_video(struct bttv *btv, struct bttv_buffer_set *set)
if (!V4L2_FIELD_HAS_BOTH(item->vb.field) &&
(item->vb.queue.next != &btv->capture)) {
item = list_entry(item->vb.queue.next, struct bttv_buffer, vb.queue);
+ /* Mike Isely <isely@pobox.com> - Only check
+ * and set up the bottom field in the logic
+ * below. Don't ever do the top field. This
+ * of course means that if we set up the
+ * bottom field in the above code that we'll
+ * actually skip a field. But that's OK.
+ * Having processed only a single buffer this
+ * time, then the next time around the first
+ * available buffer should be for a top field.
+ * That will then cause us here to set up a
+ * top then a bottom field in the normal way.
+ * The alternative to this understanding is
+ * that we set up the second available buffer
+ * as a top field, but that's out of order
+ * since this driver always processes the top
+ * field first - the effect will be the two
+ * buffers being returned in the wrong order,
+ * with the second buffer also being delayed
+ * by one field time (owing to the fifo nature
+ * of videobuf). Worse still, we'll be stuck
+ * doing fields out of order now every time
+ * until something else causes a field to be
+ * dropped. By effectively forcing a field to
+ * drop this way then we always get back into
+ * sync within a single frame time. (Out of
+ * order fields can screw up deinterlacing
+ * algorithms.) */
if (!V4L2_FIELD_HAS_BOTH(item->vb.field)) {
- if (NULL == set->top &&
- V4L2_FIELD_TOP == item->vb.field) {
- set->top = item;
- }
if (NULL == set->bottom &&
V4L2_FIELD_BOTTOM == item->vb.field) {
set->bottom = item;