media: controls: Add validate failure debug message

Add a debug message for control validation (validate_new)
failures. This is useful to debug issues with ioctls such
as VIDIOC_TRY_EXT_CTRLS and VIDIOC_S_EXT_CTRLS.
Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

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

@@ -4112,8 +4112,13 @@ static int try_set_ext_ctrls_common(struct v4l2_fh *fh,
 			struct v4l2_ctrl *ctrl = helpers[idx].ref->ctrl;
 
 			ret = user_to_new(cs->controls + idx, ctrl);
-			if (!ret && ctrl->is_ptr)
+			if (!ret && ctrl->is_ptr) {
 				ret = validate_new(ctrl, ctrl->p_new);
+				if (ret)
+					dprintk(vdev,
+						"failed to validate control %s (%d)\n",
+						v4l2_ctrl_get_name(ctrl->id), ret);
+			}
 			idx = helpers[idx].next;
 		} while (!ret && idx);