Hi All,
I wrote a simple character linux device driver (2.6 kernel) for paralel port and tried to glow the led's by connecting them to paralel port pins.But before requesting for io port 0x378 , I rmmod parportpc.ko and parport.ko and then insmod my own module,, it works fine i.e no error was given but outb() unable to glow the led's.Can anybody tell me What's the problem?

Thanks
Avinash Kharbanda

Welcome to LinuxQuestions.
Not really... Without details it is difficult to provide help.
Even though your module loaded without errors does not mean it works.
Your LEDs may not be wired correctly or you did not use the proper resister for current limiting and have burned out the parallel port.

Hi,
This is the code for the driver which i wrote :

//-----------------------------------------------------------/

#include<linux/kernel.h>
#include<linux/module.h>
#include<linux/init.h>
#include<linux/fs.h>
#include<linux/types.h>
#include<linux/kdev_t.h>
#include<linux/cdev.h>
#include<asm/uaccess.h>
#include<linux/sched.h>
#include<linux/ioport.h>
#include<linux/interrupt.h>
#include<asm/io.h>

#define PORT 0x378
unsigned int SHORT_IRQ = 7;
unsigned int check_reg = 0;

MODULE_LICENSE("GPL");

dev_t dev;//DEVICE_NUMBER
unsigned char *short_buffer = 0;


// Short's interrupt handler

irqreturn_t short_interrupt_handler (int irq, void *dev_id)
{
printk (KERN_ALERT "Short recieved an interrupt");
return 0;
}

/////////////////////////////


int short_open(struct inode *inode , struct file *filp)
{
short_buffer = kmalloc(1,GFP_KERNEL);

if(short_buffer == 0)
{
printk(KERN_ALERT "Unable to allocate memory");
return -1;
}

// Requesting Port

if(!request_region(PORT,1,"short"))
{
printk(KERN_INFO "short unable to use 0x378 Port");
return -1;
}
else
{
printk(KERN_INFO "short can now use 0x378 Port");
check_reg = 1;
}
////////////////////////////////////////


// Requesting the IRQ Number


if(request_irq(SHORT_IRQ , short_interrupt_handler , SA_INTERRUPT , "short" , NULL))
{
printk(KERN_INFO "short can't get assigned IRQ\n");
SHORT_IRQ = 0;
kfree(short_buffer);
release_region(PORT,1);
return -1;
}
else
{
printk("short is now enabling pnp: 0:7 device");
outb(0x10 , PORT+2);
}

////////////////////////////


return 0;
}

int short_release(struct inode * inode , struct file *filp)
{
if(short_buffer)
{
kfree(short_buffer);
}

if(check_reg)
release_region(PORT,1);

if(SHORT_IRQ == 7)
free_irq(SHORT_IRQ , NULL);

return 0;
}


ssize_t short_read(struct file *filp , char __user *user_buffer , size_t count , loff_t *f_pos)
{
int result = -1;

if(count != 1)
{
printk(KERN_ALERT "Read request failed due to improper count parameter passed");
return result;
}





if(short_buffer)
{
result = copy_to_user(user_buffer , short_buffer , count);
if(result)
{
return -1;
}
else
{
printk(KERN_INFO "\nProcess issued Read :%s\n",current->comm);
}

}

return count;
}



ssize_t short_write(struct file *filp , const char __user *user_buffer , size_t count , loff_t *f_pos)
{
int result = -1;

if(count != 1)
{
printk(KERN_ALERT "Write request failed due to improper count parameter passed");
return result;
}
else
{
printk(KERN_ALERT "Write request passed count parameter");
}

if(short_buffer)
{
result = copy_from_user(short_buffer, user_buffer , count);
if(result)
{
printk(KERN_ALERT "Write request failed due to copy_from_user");

return -1;
}
else
{
printk(KERN_INFO "\nProcess issued Write:%s\n",current->comm);
}

//Writing to port

outb(*short_buffer,PORT);

//////////////////
}

return count;
}



// Registering the file operations with VFS

struct file_operations short_fops = {
.owner = THIS_MODULE,
.read = short_read,
.write= short_write,
.open= short_open,
.release=short_release,
};


static int __init short_init(void)
{

int result;
struct cdev *short_cdev;//For registering the device

// Getting a Major Number Dynamically .....

result = alloc_chrdev_region(&dev,0,1,"short");

if(result < 0)
{
printk(KERN_WARNING "short did'nt got any Major number");
return result;
}
else
{
printk(KERN_INFO "short got Major Number as %d",MAJOR(dev));
}

/////////////////////////////////////////

// Registering the short

short_cdev = cdev_alloc();

short_cdev->owner = THIS_MODULE;
short_cdev->ops = &short_fops;

result = cdev_add(short_cdev,dev,1);

if(result)
{
printk(KERN_NOTICE "short unable to add");
return -1;
}

////////////////////////////////////////

return 0;
}

static void __exit short_exit(void)
{
unregister_chrdev_region(dev,1);
}

module_init(short_init);
module_exit(short_exit);


//----------------------------------------------------------/

1)Initially I loaded the module short.ko using insmod
2)made the file with Major Number received dynamically.
3)rmmoded the parport & parportpc.
4)then I wrote an application program that wud write on this file.
5)the printk(KERN_INFO "\nProcess issued Write:%s\n",current->comm); line
in short_write got executed but Led's did'nt glow.

Can u plz help me out.

Sorry, I am unable to take to time to look at your driver. Hopefully someone else might.

neither can I, but are you sure that the x86 chip has an IOPL which will allow you to output you byte or whatever>?