v4l2bufferpool: Handle resolution change event

This patch adds the detection, dequeuing and reporting of the SOURCE_CHANGE
event when the CH_RESOLUTION flag is set. The acquire function will now return
a new custom success called GST_V4L2_FLOW_RESOLUTION_CHANGE. In order to use
this new feature, elements must enable it by calling:

  gst_v4l2_buffer_pool_enable_resolution_change (pool);

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-good/-/merge_requests/870>

2 files changed, 56 insertions, 4 deletions

diff --git a/sys/v4l2/gstv4l2bufferpool.c b/sys/v4l2/gstv4l2bufferpool.c
index 21efd3572..8d2481902 100644
--- a/sys/v4l2/gstv4l2bufferpool.c
+++ b/sys/v4l2/gstv4l2bufferpool.c
@@ -1115,6 +1115,22 @@ again:
   if (gst_poll_fd_has_error (pool->poll, &pool->pollfd))
     goto select_error;
 
+  /* PRI is used to signal that events are available */
+  if (gst_poll_fd_has_pri (pool->poll, &pool->pollfd)) {
+    struct v4l2_event event = { 0, };
+
+    if (!gst_v4l2_dequeue_event (pool->obj, &event))
+      goto dqevent_failed;
+
+    if (event.type != V4L2_EVENT_SOURCE_CHANGE ||
+        (event.u.src_change.changes & V4L2_EVENT_SRC_CH_RESOLUTION) == 0) {
+      GST_INFO_OBJECT (pool, "Received unhandled event, ignoring.");
+      goto again;
+    }
+
+    return GST_V4L2_FLOW_RESOLUTION_CHANGE;
+  }
+
   if (ret == 0)
     goto no_buffers;
 
@@ -1134,7 +1150,15 @@ select_error:
     return GST_FLOW_ERROR;
   }
 no_buffers:
-  return GST_V4L2_FLOW_LAST_BUFFER;
+  {
+    return GST_V4L2_FLOW_LAST_BUFFER;
+  }
+dqevent_failed:
+  {
+    GST_ELEMENT_ERROR (pool->obj->element, RESOURCE, READ, (NULL),
+        ("dqevent error: %s (%d)", g_strerror (errno), errno));
+    return GST_FLOW_ERROR;
+  }
 }
 
 static GstFlowReturn
@@ -1241,6 +1265,11 @@ gst_v4l2_buffer_pool_dqbuf (GstV4l2BufferPool * pool, GstBuffer ** buffer,
     goto done;
   }
 
+  if (res == GST_V4L2_FLOW_RESOLUTION_CHANGE) {
+    GST_INFO_OBJECT (pool, "Resolution change detected.");
+    goto done;
+  }
+
   GST_LOG_OBJECT (pool, "dequeueing a buffer");
 
   res = gst_v4l2_allocator_dqbuf (pool->vallocator, &group);
@@ -2159,3 +2188,21 @@ gst_v4l2_buffer_pool_flush (GstBufferPool * bpool)
 
   return ret;
 }
+
+/**
+ * gst_v4l2_buffer_pool_enable_resolution_change:
+ * @pool: a #GstBufferPool
+ *
+ * When this is called, the pool will subscribe to the
+ * %V4L2_EVENT_SOURCE_CHANGE. Upon receiving this event, it will notify
+ * the element acquiring buffer with the special flow return
+ * %GST_V4L2_FLOW_RESOLUTION_CHANGE.
+ */
+void
+gst_v4l2_buffer_pool_enable_resolution_change (GstV4l2BufferPool * pool)
+{
+  g_return_if_fail (!gst_buffer_pool_is_active (GST_BUFFER_POOL (pool)));
+
+  if (gst_v4l2_subscribe_event (pool->obj, V4L2_EVENT_SOURCE_CHANGE))
+    gst_poll_fd_ctl_pri (pool->poll, &pool->pollfd, TRUE);
+}
diff --git a/sys/v4l2/gstv4l2bufferpool.h b/sys/v4l2/gstv4l2bufferpool.h
index f8972b641..b61a6ea82 100644
--- a/sys/v4l2/gstv4l2bufferpool.h
+++ b/sys/v4l2/gstv4l2bufferpool.h
@@ -41,9 +41,8 @@ G_BEGIN_DECLS
 #define GST_V4L2_BUFFER_POOL(obj)      (G_TYPE_CHECK_INSTANCE_CAST ((obj), GST_TYPE_V4L2_BUFFER_POOL, GstV4l2BufferPool))
 #define GST_V4L2_BUFFER_POOL_CAST(obj) ((GstV4l2BufferPool*)(obj))
 
-/* This flow return is used to indicated that the last buffer of a
- * drain or a resoltuion change has been found. This should normally
- * only occur for mem-2-mem devices. */
+/* This flow return is used to indicate that the last buffer has been dequeued
+ * during draining. This should normally only occur for mem-2-mem devices. */
 #define GST_V4L2_FLOW_LAST_BUFFER GST_FLOW_CUSTOM_SUCCESS
 
 /* This flow return is used to indicated that the returned buffer was marked
@@ -51,6 +50,10 @@ G_BEGIN_DECLS
  * simply waiting for next buffer. */
 #define GST_V4L2_FLOW_CORRUPTED_BUFFER GST_FLOW_CUSTOM_SUCCESS_1
 
+/* This flow return is used to indicate that a SOURCE_CHANGE event with the
+ * resolution change flag set was received. */
+#define GST_V4L2_FLOW_RESOLUTION_CHANGE GST_FLOW_CUSTOM_SUCCESS_2
+
 struct _GstV4l2BufferPool
 {
   GstBufferPool parent;
@@ -114,6 +117,8 @@ gboolean            gst_v4l2_buffer_pool_flush   (GstBufferPool *pool);
 
 gboolean            gst_v4l2_buffer_pool_orphan  (GstBufferPool ** pool);
 
+void                gst_v4l2_buffer_pool_enable_resolution_change (GstV4l2BufferPool *self);
+
 G_END_DECLS
 
 #endif /*__GST_V4L2_BUFFER_POOL_H__ */