From b706103fab54d38136ca234cb6013d782651d59f Mon Sep 17 00:00:00 2001
From: Nicolas Dufresne <nicolas.dufresne@collabora.co.uk>
Date: Fri, 5 Sep 2014 08:29:20 -0400
Subject: [PATCH] v4l2: Detect bad drivers timestamps

Even though the UVC driver do a great deal of effort to prevent bad
timestamp to be sent to userspace, there still exist UVC hardware that
are so buggy that the timestamp endup nearly random. This code detect
and ignore timestamp from these drivers, making these camera usable.
This has been tested on both invalid and valid cameras, making sure it
does not trigger for valid cameras.

https://bugzilla.gnome.org/show_bug.cgi?id=732910
---
 sys/v4l2/gstv4l2src.c | 46 ++++++++++++++++++++++++++++++++++++++++------
 sys/v4l2/gstv4l2src.h |  4 ++++
 2 files changed, 44 insertions(+), 6 deletions(-)

diff --git a/sys/v4l2/gstv4l2src.c b/sys/v4l2/gstv4l2src.c
index e1c0df0..8a4155c 100644
--- a/sys/v4l2/gstv4l2src.c
+++ b/sys/v4l2/gstv4l2src.c
@@ -561,6 +561,9 @@ gst_v4l2src_start (GstBaseSrc * src)
   v4l2src->ctrl_time = 0;
   gst_object_sync_values (GST_OBJECT (src), v4l2src->ctrl_time);
 
+  v4l2src->has_bad_timestamp = FALSE;
+  v4l2src->last_timestamp = 0;
+
   return TRUE;
 }
 
@@ -575,6 +578,9 @@ static gboolean
 gst_v4l2src_unlock_stop (GstBaseSrc * src)
 {
   GstV4l2Src *v4l2src = GST_V4L2SRC (src);
+
+  v4l2src->last_timestamp = 0;
+
   return gst_v4l2_object_unlock_stop (v4l2src->v4l2object);
 }
 
@@ -670,7 +676,8 @@ gst_v4l2src_create (GstPushSrc * src, GstBuffer ** buf)
     abs_time = GST_CLOCK_TIME_NONE;
   }
 
-  if (timestamp != GST_CLOCK_TIME_NONE) {
+retry:
+  if (!v4l2src->has_bad_timestamp && timestamp != GST_CLOCK_TIME_NONE) {
     struct timespec now;
     GstClockTime gstnow;
 
@@ -680,7 +687,7 @@ gst_v4l2src_create (GstPushSrc * src, GstBuffer ** buf)
     clock_gettime (CLOCK_MONOTONIC, &now);
     gstnow = GST_TIMESPEC_TO_TIME (now);
 
-    if (gstnow < timestamp && (timestamp - gstnow) > (10 * GST_SECOND)) {
+    if (timestamp > gstnow || (gstnow - timestamp) > (10 * GST_SECOND)) {
       GTimeVal now;
 
       /* very large diff, fall back to system time */
@@ -688,12 +695,39 @@ gst_v4l2src_create (GstPushSrc * src, GstBuffer ** buf)
       gstnow = GST_TIMEVAL_TO_TIME (now);
     }
 
-    if (gstnow > timestamp) {
-      delay = gstnow - timestamp;
-    } else {
-      delay = 0;
+    /* Detect buggy drivers here, and stop using their timestamp. Failing any
+     * of these condition would imply a very buggy driver:
+     *   - Timestamp in the future
+     *   - Timestamp is going backward compare to last seen timestamp
+     *   - Timestamp is jumping forward for less then a frame duration
+     *   - Delay is bigger then the actual timestamp
+     * */
+    if (timestamp > gstnow) {
+      GST_WARNING_OBJECT (v4l2src,
+          "Timestamp in the future detected, ignoring driver timestamps");
+      v4l2src->has_bad_timestamp = TRUE;
+      goto retry;
+    }
+
+    if (v4l2src->last_timestamp > timestamp) {
+      GST_WARNING_OBJECT (v4l2src,
+          "Timestamp going backward, ignoring driver timestamps");
+      v4l2src->has_bad_timestamp = TRUE;
+      goto retry;
     }
 
+    delay = gstnow - timestamp;
+
+    if (delay > timestamp) {
+      GST_WARNING_OBJECT (v4l2src,
+          "Timestamp does not correlate with any clock, ignoring driver timestamps");
+      v4l2src->has_bad_timestamp = TRUE;
+      goto retry;
+    }
+
+    /* Save last timestamp for sanity checks */
+    v4l2src->last_timestamp = timestamp;
+
     GST_DEBUG_OBJECT (v4l2src, "ts: %" GST_TIME_FORMAT " now %" GST_TIME_FORMAT
         " delay %" GST_TIME_FORMAT, GST_TIME_ARGS (timestamp),
         GST_TIME_ARGS (gstnow), GST_TIME_ARGS (delay));
diff --git a/sys/v4l2/gstv4l2src.h b/sys/v4l2/gstv4l2src.h
index 36915cb..2d90553 100644
--- a/sys/v4l2/gstv4l2src.h
+++ b/sys/v4l2/gstv4l2src.h
@@ -60,6 +60,10 @@ struct _GstV4l2Src
   guint64 offset;
 
   GstClockTime ctrl_time;
+
+  /* Timestamp sanity check */
+  GstClockTime last_timestamp;
+  gboolean has_bad_timestamp;
 };
 
 struct _GstV4l2SrcClass
-- 
2.7.4