October 11, 2010

Parallel port driver not working?!

Hello everyone!
I've been doing some kernel module development for Linux lately, and I figured: Why not make a 6V LED light up?
So I hooked up to wires with the LED and plugged the wires into hole/pin 2 and 25 (data0 and GND respectively) of my parallel port. Now all I needed was the device driver.. now the device driver is done..... it's not working.
I have tested my homegrown "LED hardware" standalone with a 1.5V battery, which did make the LED glow slightly, so the 5V of the parallel port should definitely make it glow!
I have made a virtual device using 'mknod' to communicate with the parallel port at 0x378 (confirmed, by the way).
This is my mknod command: "sudo mknod /dev/parlelport c 61 0", and finally, to make the "device" accessible to anyone: "sudo chmod 666 /dev/parlelport".
I can not insert the module with parport_pc running, so I remove that and the modules using it, before I 'insmod' my kernel module, which looks like this:

#include <linux/module.h>
#include <linux/fs.h>
#include <asm/uaccess.h>
#include <asm/io.h>

ssize_t driver_read(struct file *filp, char *buf, size_t count, loff_t *f_pos);
ssize_t driver_write(struct file *filp, char *buf, size_t count, loff_t *f_pos);
int driver_open(struct inode *inode, struct file *filp);
int driver_release(struct inode *inode, struct file *filp);

int major = 61;
int port;

struct file_operations f_ops = {
read: driver_read,
write: driver_write,
open: driver_open,
release: driver_release

void driver_exit(void){
unregister_chrdev(major, "parlelport");

release_region(0x378, 1);

printk("<parallel_port_module>: Removing...\n");

int driver_init(void){
int result;
result = register_chrdev(major, "parlelport", &f_ops);

if(result < 0){
printk("<parallel_port_module>: Unable to register module!\n");
return result;

port = check_region(0x378, 1);

printk("<parallel_port_module>: Requested region already reserved!\n");
result = port;
goto fail;

request_region(0x378, 1, "parlelport");
printk("<parallel_port_module>: Inserting...\n");
return 0;

return result;

ssize_t driver_read(struct file *filp, char *buf, size_t count, loff_t *f_pos){
char buffer;
int status;
buffer = inb(0x378);
status = copy_to_user(buf, &buffer, 1);

case 0:
printk("%i\n", buffer);

if(*f_pos == 0){
*f_pos += 1;
return 0;
return 0;

ssize_t driver_write(struct file *filp, char *buf, size_t count, loff_t *f_pos){
char *tmp;
char buffer;
int status;
tmp = buf + count - 1;

status = copy_from_user(&buffer, tmp, 1);
outb(buffer, 0x378);

if(status == 0){
printk("%i\n", buffer);

return 1;

int driver_open(struct inode *inode, struct file *filp){
return 0;

int driver_release(struct inode *inode, struct file *filp){
return 0;

MODULE_AUTHOR("Benjamin D####");

I DO get a "/home/benjamin/Documents/c/kernel/parlelport/parlelport.c:16: warning: initialization from incompatible pointer type" waning when compiling from my Makefile though.. I don't know to fix it..

Line 16: write: driver_write,

Apparently it does register, reserve, and initialize correctly but something with the data in/outputs just doesn't seem right...
As you can see my read and write functions log the data they in/output, and when doing an 'echo -n A >/dev/parlelport' followed by a 'cat /dev/parlelport', this shows up in my system log, NO MATTER WHAT DATA I WRITE TO THE DEVICE:

[ 1962.448227]
: Inserting...
[ 1985.132240] 65
[ 1994.501861] -1

Only '65' might change depending on what char I sent too the parlelport device, but I always receive -1 from the parallel port.....

Click Here!