media: v4l: subdev: Improve link format validation debug messages

The existing link format validation failure debug message in media-entity.c
helped to pinpoint the point of failure but provided no additional
information what's wrong. Tell the user exactly why the validation failed.
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

drivers/media/v4l2-core/v4l2-subdev.c

@@ -792,21 +792,55 @@ int v4l2_subdev_link_validate_default(struct v4l2_subdev *sd,
 				      struct v4l2_subdev_format *source_fmt,
 				      struct v4l2_subdev_format *sink_fmt)
 {
+	bool pass = true;
+
 	/* The width, height and code must match. */
-	if (source_fmt->format.width != sink_fmt->format.width
-	    || source_fmt->format.height != sink_fmt->format.height
-	    || source_fmt->format.code != sink_fmt->format.code)
-		return -EPIPE;
+	if (source_fmt->format.width != sink_fmt->format.width) {
+		dev_dbg(sd->entity.graph_obj.mdev->dev,
+			"%s: width does not match (source %u, sink %u)\n",
+			__func__,
+			source_fmt->format.width, sink_fmt->format.width);
+		pass = false;
+	}
+
+	if (source_fmt->format.height != sink_fmt->format.height) {
+		dev_dbg(sd->entity.graph_obj.mdev->dev,
+			"%s: height does not match (source %u, sink %u)\n",
+			__func__,
+			source_fmt->format.height, sink_fmt->format.height);
+		pass = false;
+	}
+
+	if (source_fmt->format.code != sink_fmt->format.code) {
+		dev_dbg(sd->entity.graph_obj.mdev->dev,
+			"%s: media bus code does not match (source 0x%8.8x, sink 0x%8.8x)\n",
+			__func__,
+			source_fmt->format.code, sink_fmt->format.code);
+		pass = false;
+	}
 
 	/* The field order must match, or the sink field order must be NONE
 	 * to support interlaced hardware connected to bridges that support
 	 * progressive formats only.
 	 */
 	if (source_fmt->format.field != sink_fmt->format.field &&
-	    sink_fmt->format.field != V4L2_FIELD_NONE)
-		return -EPIPE;
+	    sink_fmt->format.field != V4L2_FIELD_NONE) {
+		dev_dbg(sd->entity.graph_obj.mdev->dev,
+			"%s: field does not match (source %u, sink %u)\n",
+			__func__,
+			source_fmt->format.field, sink_fmt->format.field);
+		pass = false;
+	}
 
-	return 0;
+	if (pass)
+		return 0;
+
+	dev_dbg(sd->entity.graph_obj.mdev->dev,
+		"%s: link was \"%s\":%u -> \"%s\":%u\n", __func__,
+		link->source->entity->name, link->source->index,
+		link->sink->entity->name, link->sink->index);
+
+	return -EPIPE;
 }
 EXPORT_SYMBOL_GPL(v4l2_subdev_link_validate_default);