With Linux kernel version 3.3 or later, qemu fails with the following message:

sh_serial: unsupported read from 0x18
  Aborted
Reported-and-analyzed-by: NRob Landley <rob@landley.net>
Signed-off-by: NGuenter Roeck <linux@roeck-us.net>
Reviewed-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>