i've been reading 'linux device drivers', i finally finished the interrupt chapter so it's time to finally write some sort of driver. i figured a mouse would be easiest, so i've been checking out the mouse code. i have some questions:

+there are many busmouse drivers in [ drivers/char/ ] that all use the functions defined in [ drivers/char/busmouse.c ] to register a busmouse.
+my mouse driver is [ drivers/input/mousedev.c ]

my question is, what is the difference between these types? is a busmouse something different? with the busmice, writing a driver seems pretty simple and all you do is provide an open/close method and the rest is done for you just by calling register_busmouse(). the mousedev driver is much more complex.
i keep trying to google to find out what exactly a busmouse is, but all i find is this same 'liinux busmouse HOWTO' guide.