Results in this tree /sys/class/input with a combined keyboard/mouse
USB device:

[root@w-hlinder2 input]# tree /sys/class/input
/sys/class/input
|-- devices
|   |-- 0 -> ../../../devices/pci0/00:0f.2/usb1/1-1/1-1.1/1-1.1:0
|   |-- 1 -> ../../../devices/pci0/00:0f.2/usb1/1-1/1-1.1/1-1.1:1
|   `-- 2 -> ../../../devices/pci0/00:0f.2/usb1/1-1/1-1.2/1-1.2:0
|-- drivers
|   `-- usb:hid -> ../../../bus/usb/drivers/hid
`-- mouse