v4l2bufferpool: Update pool limit with hardware requiremenst

If the driver need more buffers than requested by the config,
update the pool min/max values. The minimum value for the pool
could be provided either by the driver or by the pool. This is
best effort for drivers that don't support
CID V4L2_CID_MIN_BUFFERS_FOR_CAPTURE.

https://bugzilla.gnome.org/show_bug.cgi?id=730200

sys/v4l2/gstv4l2bufferpool.c

@@ -668,9 +668,9 @@ gst_v4l2_buffer_pool_start (GstBufferPool * bpool)
         copy_threshold =
             MAX (GST_V4L2_MIN_BUFFERS, obj->min_buffers_for_capture);
 
-        /* Ensure GstBufferPool don't expect initial minimum */
-        if (min_buffers > count)
-          min_buffers = count;
+        /* The initial minimum could be provide either by GstBufferPool or
+         * driver needs. */
+        min_buffers = count;
       }
 
       break;
@@ -696,7 +696,7 @@ gst_v4l2_buffer_pool_start (GstBufferPool * bpool)
         goto no_buffers;
       }
 
-      num_buffers = count;
+      min_buffers = num_buffers = count;
       break;
     }
     case GST_V4L2_IO_DMABUF_IMPORT:
@@ -720,7 +720,7 @@ gst_v4l2_buffer_pool_start (GstBufferPool * bpool)
         goto no_buffers;
       }
 
-      num_buffers = count;
+      min_buffers = num_buffers = count;
       break;
     }
     default:
@@ -735,6 +735,9 @@ gst_v4l2_buffer_pool_start (GstBufferPool * bpool)
   pool->num_buffers = num_buffers;
   pool->num_queued = 0;
 
+  if (max_buffers < min_buffers)
+    max_buffers = min_buffers;
+
   gst_buffer_pool_config_set_params (config, caps, size, min_buffers,
       max_buffers);
   GST_BUFFER_POOL_CLASS (parent_class)->set_config (bpool, config);