If you insmod bpwd_drv.ko and see "Error: could not insert module bpwd_drv.ko: Input/output error.", you can refer to the following steps to try.
1. make clean.
2. cat /proc/devices and check number 247.
3. If number exist, run rm –rf /dev/bpwd_drv and then mknod /dev/bpwd_drv c xxx 0 (e.g. = mknod /dev/plcm_drv c 240 0, number 240 doesn’t exist in /proc/devices)
5. insmod bpwd_drv.ko.