according to your solution, it is because the kernel module hasn't been loaded.
you put "psmouse proto=bare" into /etc/modules to force the kernel to load the module when booting up.
#
# Hardware I/O ports
#
CONFIG_SERIO=y
CONFIG_SERIO_I8042=y
CONFIG_SERIO_SERPORT=y
# CONFIG_SERIO_CT82C710 is not set
CONFIG_SERIO_PCIPS2=y
CONFIG_SERIO_LIBPS2=y
#CONFIG_SERIO_RAW is not set
# CONFIG_GAMEPORT is not set