I/O port control GPIO output square wave of 1.5khz

I need GPIO 31 output square wave of 1.5 khz. if i use gpio_set_value() control it output 1 or 0,it can only output square wave of 0.25 khz .so I want to use request_region() and outw() to control directly the PREG_PAD_GPIO5_O register(0xff634421).however,system always reboot.and output "Unable to handle kernel paging request at virtual address fee34421.
this is my copy


outw(0x08, 0xff634421)