$ v4l-conf
v4l-conf: using X11 display :0
dga: version 2.0
X Error of failed request:  XF86DGANoDirectVideoMode
  Major opcode of failed request:  136 (XFree86-DGA)
  Minor opcode of failed request:  1 (XF86DGAGetVideoLL)
  Serial number of failed request:  13
  Current serial number in output stream:  13