Accessing the parallel port hardware on linux - c

Question

I wrote a parallel port Linux device driver but I cant access the parallel port hardware
#include <linux/init.h>
#include <linux/autoconf.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/fs.h>
#include <linux/errno.h>
#include <linux/types.h>
#include <linux/proc_fs.h>
#include <linux/fcntl.h>
#include <linux/ioport.h>
#include <asm/system.h>
#include <asm/uaccess.h>
#include <asm/io.h>
#define DRVNAME "parportleds"
#define BASEPORT 0x378
MODULE_LICENSE("Dual BSD/GPL");
MODULE_AUTHOR("Ganesh");
MODULE_DESCRIPTION("Parallel port LED driver.");
int parportleds_open(struct inode *inode, struct file *filp);
int parportleds_release(struct inode *inode, struct file *filp);
ssize_t parportleds_read(struct file *filp,char *buf,size_t count, loff_t *f_pos);
ssize_t parportleds_write(struct file *filp, const char *buf,size_t count, loff_t *f_pos);
void parportleds_exit(void);
int parportleds_init(void);
struct file_operations parportleds_fops = {
read: parportleds_read,
write: parportleds_write,
open: parportleds_open,
release: parportleds_release
};
int parportleds_major = 61;
int port;
module_init(parportleds_init);
module_exit(parportleds_exit);
int parportleds_init(void) {
int result;
result = register_chrdev(parportleds_major, DRVNAME,&parportleds_fops);
if (result < 0) {
printk("<1>parport: cannot obtain major number %d\n",parportleds_major);
return result;
}
port = check_region(BASEPORT, 1);
if (port) {
printk("<1>parportleds: cannot reserve 0x378 \n");
result = port;
goto fail;
}
request_region(BASEPORT, 1, DRVNAME);
printk("<1>Inserting parportled module\n");
return 0;
fail:
parportleds_exit();
return result;
}
void parportleds_exit(void) {
unregister_chrdev(parportleds_major, DRVNAME);
if (!port) {
release_region(BASEPORT,1);
}
printk("<1>Removing module parportleds\n");
}
int parportleds_open(struct inode *inode, struct file *filp) {
return 0;
}
int parportleds_release(struct inode *inode, struct file *filp) {
return 0;
}
ssize_t parportleds_read(struct file *filp, char *buf,size_t count, loff_t *f_pos) {
char parportleds_buffer;
parportleds_buffer = inb(BASEPORT);
copy_to_user(buf,&parportleds_buffer,1);
if (*f_pos == 0) {
*f_pos+=1;
return 1;
} else {
return 0;
}
}
ssize_t parportleds_write( struct file *filp, const char *buf, size_t count, loff_t *f_pos) {
char *tmp;
char parportleds_buffer;
tmp=(char *)buf+count-1;
copy_from_user(&parportleds_buffer,tmp,1);
outb(parportleds_buffer,BASEPORT);
printk("<1>parport write: %d\n",parportleds_buffer);
return 1;
}
This is my code when I try to read and write to /dev/parportleds am getting a sucess msg in dmesg
But when i try to make a pin high of parallel port using echo 3 > /dev/parportleds
The voltage of the datapins of paralleport remains same.
can anyone help me to fix this issue.
its my first attempt to write device drivers.

Answer 1

A couple of notes first:
1) Take note of InternetSeriousBusiness' comment: when you echo a character to your char device, the device will receive the ASCII encoded bit pattern. Look at an ASCII table to see which character you need to send to get the bit pattern you want.
2) You mentioned that when you send a bit pattern, the output voltage doesn't change. What about the other direction? Does the value you read accurately reflect voltages applied to the pins, or are those off to? If yes, then you know problem has something to do with writing. If no, then you may not even be connected to the port the way you think you are.
My Answer:
Buffers that interact with user data should have the __user tag attached. For example, the argument list of parportleds_write(), should look like this:
ssize_t parportleds_write(struct file *fp, const char __user *buf, ssize_t count, loff_t *f_pos){
Your call to copy_from_user() may be failing because this is missing. The __user tag should be added to your read function as well.