The following patch allows the use of SERIAL_CONSOLES to create multiple getty sessions on different serial ports: http://git.yoctoproject.org/cgit/cgit.cgi/poky/commit/?id=7dec9be56bed73bbd8cbc42360620c64f1fed882

The inittab IDs used by the patch are not unique because the same IDs are used elsewhere in the poky/meta/recipes-core/sysvinit/sysvinit-inittab_2.88dsf.bb recipe:

        for n in ${SYSVINIT_ENABLED_GETTYS}
        do
            echo "$n:2345:respawn:${base_sbindir}/getty 38400 tty$n" >> ${D}${sysconfdir}/inittab
        done
        echo "" >> ${D}${sysconfdir}/inittab

This results in myltiple lines in the inittab having the same ID which will cause a conflict.

I suggest that the patch be modified to use the IDs S0,S1,..,SN rather than 1,2,..,N as it is currently. 

echo "S${idx}:2345:respawn:${base_sbindir}/getty ${j}" >> ${D}${sysconfdir}/inittab