ASYNC_SPLIT_TERMIOS behavior is a remnant of the long-dead /dev/cuaXX
callout device. Split termios handling was removed tree-wide in v2.5.71 by:

commit 99a21ede
Author: Alexander Viro <viro@www.linux.org.uk>
Date:   Wed Jun 11 07:41:28 2003 -0700

    [PATCH] tty_driver refcounting

    killed the last remnants of callout stuff - we don't need to mess with
    storing termios privately anymore.

which pre-dated the re-introduction into the cris serial driver
in v2.6.7 by:

commit 311a5ffe
Author: Andrew Morton <akpm@osdl.org>
Date:   Mon May 31 18:52:29 2004 -0700

    [PATCH] CRIS architecture update

    From: "Mikael Starvik" <mikael.starvik@axis.com>

    - Lots of fixes from 2.4.

    - Updated for 2.6.6.

    - Added IDE driver

Cc: Mikael Starvik <starvik@axis.com>
Cc: Jesper Nilsson <jesper.nilsson@axis.com>
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>