shortprint.c

Linux Device Drivers 2nd 经典书籍的配套源码

/*
 * A version of the "short" driver which drives a parallel printer directly,
 * with a lot of simplifying assumptions.
 *
 * Copyright (C) 2001 Alessandro Rubini and Jonathan Corbet
 * Copyright (C) 2001 O'Reilly & Associates
 *
 * The source code in this file can be freely used, adapted,
 * and redistributed in source or binary form, so long as an
 * acknowledgment appears in derived source files.  The citation
 * should list that the code comes from the book "Linux Device
 * Drivers" by Alessandro Rubini and Jonathan Corbet, published
 * by O'Reilly & Associates.   No warranty is attached;
 * we cannot take responsibility for errors or fitness for use.
 *
 * $Id: shortprint.c,v 1.4 2001/07/18 22:28:18 rubini Exp $
 */

#ifndef __KERNEL__
#  define __KERNEL__
#endif
#ifndef MODULE
#  define MODULE
#endif

#include <linux/config.h>
#include <linux/module.h>

#include <linux/sched.h>
#include <linux/kernel.h> /* printk() */
#include <linux/fs.h>     /* everything... */
#include <linux/errno.h>  /* error codes */
#include <linux/delay.h>  /* udelay */
#include <linux/malloc.h>
#include <linux/ioport.h>
#include <linux/interrupt.h>
#include <linux/tqueue.h>
#include <linux/timer.h>

#include <asm/io.h>
#include <asm/semaphore.h>
#include <asm/atomic.h>

#include "sysdep.h"
#include "shortprint.h"

#define SHORTP_NR_PORTS 3

/*
 * all of the parameters have no "shortp_" prefix, to save typing when
 * specifying them at load time
 */
static int major = 0; /* dynamic by default */
MODULE_PARM(major, "i");

/* default is the first printer port on PC's. "shortp_base" is there too
   because it's what we want to use in the code */
static unsigned long base = 0x378;
unsigned long shortp_base = 0;
MODULE_PARM(base, "l");

/* The interrupt line is undefined by default. "shortp_irq" is as above */
static int irq = -1;
static int shortp_irq = -1;
MODULE_PARM(irq, "i");

/* Microsecond delay around strobe. */
static int delay = 0;
static int shortp_delay;
MODULE_PARM(delay, "i");

MODULE_AUTHOR ("Jonathan Corbet");


/*
 * Forwards.
 */
void shortp_cleanup ();
static void shortp_timeout (unsigned long unused);

/*
 * Input is managed through a simple circular buffer which, among other things,
 * is allowed to overrun if the reader isn't fast enough.  That makes life simple
 * on the "read" interrupt side, where we don't want to block.
 */
static unsigned long shortp_in_buffer = 0;
static unsigned long volatile shortp_in_head;
static volatile unsigned long shortp_in_tail;
DECLARE_WAIT_QUEUE_HEAD(shortp_in_queue);
static struct timeval shortp_tv;  /* When the interrupt happened. */

/*
 * Atomicly increment an index into shortp_in_buffer
 */
static inline void shortp_incr_bp(volatile unsigned long *index, int delta)
{
    unsigned long new = *index + delta;
    barrier ();  /* Don't optimize these two together */
    *index = (new >= (shortp_in_buffer + PAGE_SIZE)) ? shortp_in_buffer : new;
}


/*
 * On the write side we have to be more careful, since we don't want to drop
 * data.  The semaphore is used to serialize write-side access to the buffer;
 * there is only one consumer, so read-side access is unregulated.  The
 * wait queue will be awakened when space becomes available in the buffer.
 */
unsigned char *shortp_out_buffer = NULL;
volatile unsigned char *shortp_out_head, *shortp_out_tail;
struct semaphore shortp_out_sem;
DECLARE_WAIT_QUEUE_HEAD (shortp_out_queue);

/*
 * Available space in the output buffer; should be called with the semaphore
 * held.  Returns contiguous space, so caller need not worry about wraps.
 */
static inline int shortp_out_space()
{
    if (shortp_out_head >= shortp_out_tail) {
	int space = PAGE_SIZE - (shortp_out_head - shortp_out_buffer);
	return (shortp_out_tail == shortp_out_buffer) ? space - 1 : space;
    }
    else
	return (shortp_out_tail - shortp_out_head) - 1;
}

static inline void shortp_incr_out_bp(volatile unsigned char **bp, int incr)
{
	unsigned char *new = (unsigned char *) *bp + incr;
	if (new >= (shortp_out_buffer + PAGE_SIZE))
	    new -= PAGE_SIZE;
	*bp = new;
}

/*
 * The output "process" is controlled by a spin lock; decisions on
 * shortp_output_active or manipulation of shortp_out_tail require
 * that this lock be held.
 */
static spinlock_t shortp_out_lock;
volatile static int shortp_output_active;
DECLARE_WAIT_QUEUE_HEAD (shortp_empty_queue); /* waked when queue empties */

static int nwrote = 0;

/*
 * When output is active, the timer is too, in case we miss interrupts.  Hold
 * shortp_out_lock if you mess with the timer.
 */
static struct timer_list shortp_timer;
#define TIMEOUT 5*HZ  /* Wait a long time */


/*
 * Open the device.
 */
int shortp_open (struct inode *inode, struct file *filp)
{
    MOD_INC_USE_COUNT;
    return 0;
}


int shortp_release (struct inode *inode, struct file *filp)
{
    /* Wait for any pending output to complete */
    wait_event_interruptible(shortp_empty_queue, shortp_output_active==0);

    MOD_DEC_USE_COUNT;
    return 0;
}



#ifdef __USE_OLD_SELECT__
int shortp_poll (struct inode *inode, struct file *filp,
                  int mode, select_table *table)
{
    return mode==SEL_EX ? 0 : 1; /* readable, writable, not-exceptionable */
}
#define poll select
#else /* Use poll */

unsigned int shortp_poll(struct file *filp, poll_table *wait)
{
    return POLLIN | POLLRDNORM | POLLOUT | POLLWRNORM;
}

#endif /* __USE_OLD_SELECT__ */



/*
 * The read routine, which doesn't return data from the device; instead, it
 * returns timing information just like the "short" device.
 */
ssize_t shortp_read (struct file *filp, char *buf, size_t count, loff_t *f_pos)
{
    int count0;

    while (shortp_in_head == shortp_in_tail) {
        interruptible_sleep_on(&shortp_in_queue);
        if (signal_pending (current))  /* a signal arrived */
          return -ERESTARTSYS; /* tell the fs layer to handle it */
        /* else, loop */
    }
    /* count0 is the number of readable data bytes */
    count0 = shortp_in_head - shortp_in_tail;
    if (count0 < 0) /* wrapped */
        count0 = shortp_in_buffer + PAGE_SIZE - shortp_in_tail;
    if (count0 < count) count = count0;

    if (copy_to_user(buf, (char *)shortp_in_tail, count))
	return -EFAULT;
    shortp_incr_bp (&shortp_in_tail, count);
    return count;
}


/*
 * Write the next character from the buffer.  There should *be* a next
 * character...  The spinlock should be held when this routine is called.
 */
static void shortp_do_write()
{
    unsigned char cr = inb(shortp_base + SP_CONTROL);

    /* Make sure the device is ready for us */
    if ((inb(shortp_base + SP_STATUS) & SP_SR_BUSY) == 0) {
//      printk (KERN_INFO "shortprint: waiting for printer busy\n");
//	printk (KERN_INFO "Status is 0x%x\n", inb(shortp_base + SP_STATUS));
	while ((inb(shortp_base + SP_STATUS) & SP_SR_BUSY) == 0) {
		set_current_state(TASK_INTERRUPTIBLE);
		schedule_timeout(10*HZ);
	}
		
    }

    /* Mark output active and start up our timer if need be */
    if (! shortp_output_active) {
	shortp_output_active = 1;
	shortp_timer.expires = jiffies + TIMEOUT;
	add_timer (&shortp_timer);
    }
    else
        mod_timer(&shortp_timer, jiffies + TIMEOUT);

    /* Strobe a byte out to the device */
    outb_p(*shortp_out_tail, shortp_base+SP_DATA);
    shortp_incr_out_bp(&shortp_out_tail, 1);
    if (shortp_delay) udelay(shortp_delay);
    outb_p(cr | SP_CR_STROBE, shortp_base+SP_CONTROL);
    if (shortp_delay) udelay(shortp_delay);
    outb_p(cr & ~SP_CR_STROBE, shortp_base+SP_CONTROL);
    nwrote++;
}


/*
 * Write to the device.
 */
ssize_t shortp_write (struct file *filp, const char *buf, size_t count,
                loff_t *f_pos)
{
    int space, written = 0;
    unsigned long flags;
/*
 * Take and hold the semaphore for the entire duration of the operation.  The
 * consumer side ignores it, and it will keep other data from interleaving
 * with ours.
 */
    if (down_interruptible (&shortp_out_sem))
	return -ERESTARTSYS;
/*
 * Out with the data.
 */
    while (written < count) {
        /* Hang out until some buffer space is available. */
	space = shortp_out_space();
	if (space <= 0) {
		if (wait_event_interruptible(shortp_out_queue,
				(space = shortp_out_space()) > 0)) {
		    *f_pos += written;
		    up(&shortp_out_sem);
		    return -ERESTARTSYS;
		}
	}

        /* Move data into the buffer. */
	if ((space + written) > count)
	    space = count - written;
	if (copy_from_user((char *) shortp_out_head, buf, space)) {
	    up(&shortp_out_sem);
	    return -EFAULT;
	}
	shortp_incr_out_bp(&shortp_out_head, space);
	buf += space;
	written += space;

        /* If no output is active, make it active. */
	spin_lock_irqsave(&shortp_out_lock, flags);
	if (! shortp_output_active)
 	    shortp_do_write ();
	spin_unlock_irqrestore(&shortp_out_lock, flags);
    }

    *f_pos += written;
    up(&shortp_out_sem);
    return written;
}


/*
 * The bottom-half handler.
 */

static struct tq_struct shortp_task;

void shortp_do_task (void *unused)
{
    int written;
    unsigned long flags;

    /* Keep the output going */
    spin_lock_irqsave(&shortp_out_lock, flags);
    if (shortp_out_head == shortp_out_tail) { /* empty */
        shortp_output_active = 0;
	wake_up_interruptible(&shortp_empty_queue);
	del_timer_sync(&shortp_timer);
    }
    else
	shortp_do_write();

    /* If somebody's waiting, wake them up. */
    if (((PAGE_SIZE + shortp_out_tail - shortp_out_head) % PAGE_SIZE) > SP_MIN_SPACE) {
        wake_up_interruptible(&shortp_out_queue);
    }
    spin_unlock_irqrestore(&shortp_out_lock, flags);

    /* Handle the "read" side operation */
    written = sprintf((char *)shortp_in_head, "%08u.%06u\n",
			(int)(shortp_tv.tv_sec % 100000000),
			(int)(shortp_tv.tv_usec));
    shortp_incr_bp(&shortp_in_head, written);
    wake_up_interruptible(&shortp_in_queue); /* awake any reading process */
}


/*
 * The top-half interrupt handler.
 */
void shortp_interrupt(int irq, void *dev_id, struct pt_regs *regs)
{
    if (! shortp_output_active)
	printk(KERN_INFO "shortprint: spurious interrupt\n");

    /* Remember the time, and farm off the rest to the task queue function */ 
    do_gettimeofday(&shortp_tv);
//    schedule_task(&shortp_task);
    queue_task(&shortp_task, &tq_immediate);
    mark_bh(IMMEDIATE_BH);
}

/*
 * Interrupt timeouts.  Just because we got a timeout doesn't mean that
 * things have gone wrong, however; printers can spend an awful long time
 * just thinking about things.
 */
static void shortp_timeout(unsigned long unused)
{
    unsigned long flags;
    unsigned char status;
   
    spin_lock_irqsave(&shortp_out_lock, flags);
    status = inb(shortp_base + SP_STATUS);

    /* If the printer is still busy we just reset the timer */
    if ((status & SP_SR_BUSY) == 0 || (status & SP_SR_ACK)) {
        shortp_timer.expires = jiffies + TIMEOUT;
	add_timer(&shortp_timer);
	spin_unlock_irqrestore(&shortp_out_lock, flags);
	return;
    }

    /* Otherwise we must have dropped an interrupt. */
    spin_unlock_irqrestore(&shortp_out_lock, flags);
    shortp_interrupt (shortp_irq, NULL, NULL);
}
    




/*
 * 2.0 wrappers.
 */
#ifdef LINUX_20

int shortp_read_20 (struct inode *inode, struct file *filp, char *buf,
                int count)
{
    return shortp_read (filp, buf, count, &filp->f_pos);
}

int shortp_write_20 (struct inode *inode, struct file *filp, const char *buf,
                int count)
{
    return shortp_write (filp, buf, count, &filp->f_pos);
}

void shortp_release_20 (struct inode *inode, struct file *filp)
{
    (void) shortp_release(inode, filp);
}

#define shortp_read  shortp_read_20
#define shortp_write shortp_write_20
#define shortp_release shortp_release_20

#endif /* LINUX_20 */


struct file_operations shortp_fops = {
    read: shortp_read,
    write: shortp_write,
    open: shortp_open,
    release: shortp_release,
    /* should really implement poll too */
};




/*
 * Module initialization
 */

int shortp_init(void)
{
    int result;

    /*
     * first, sort out the base/shortp_base ambiguity: we'd better
     * use shortp_base in the code, for clarity, but allow setting
     * just "base" at load time. Same for "irq".
     */
    shortp_base = base;
    shortp_irq = irq;
    shortp_delay = delay;

    /* Set up owner pointers.*/
    SET_MODULE_OWNER(&shortp_fops);

    /* Get our needed resources. */
    result = check_region(shortp_base, SP_NPORTS);
    if (result) {
	printk(KERN_INFO "shortprint: can't get I/O port address 0x%lx\n",
			shortp_base);
	return result;
    }	
    request_region(shortp_base, SHORTP_NR_PORTS, "shortprint");

    /* Register the device */
    result = register_chrdev(major, "shortprint", &shortp_fops);
    if (result < 0) {
        printk(KERN_INFO "shortp: can't get major number\n");
        release_region(shortp_base,SHORTP_NR_PORTS);
        return result;
    }
    if (major == 0) major = result; /* dynamic */

    /* Initialize the input buffer. */
    shortp_in_buffer = __get_free_pages(GFP_KERNEL,0); /* never fails */
    shortp_in_head = shortp_in_tail = shortp_in_buffer;

    /* And the output buffer. */
    shortp_out_buffer = (unsigned char *) __get_free_pages(GFP_KERNEL, 0);
    shortp_out_head = shortp_out_tail = shortp_out_buffer;
    sema_init (&shortp_out_sem, 1);
    
    /* And the output info */
    shortp_output_active = 0;
    spin_lock_init (&shortp_out_lock);
    init_timer(&shortp_timer);
    shortp_timer.function = shortp_timeout;
    shortp_timer.data = 0;
    
    /* Fill the shortp_task structure, used for the bottom half handler. */
    shortp_task.routine = shortp_do_task;
    shortp_task.data = NULL; /* unused */

    /* If no IRQ was explicitly requested, pick a default */
    if (shortp_irq < 0)
        switch(shortp_base) {
          case 0x378: shortp_irq = 7; break;
          case 0x278: shortp_irq = 2; break;
          case 0x3bc: shortp_irq = 5; break;
        }

    /* Request the IRQ */
    result = request_irq(shortp_irq, shortp_interrupt, 0, "shortprint", NULL);
    if (result) {
        printk(KERN_INFO "shortprint: can't get assigned irq %i\n",
			shortp_irq);
	shortp_irq = -1;
	shortp_cleanup ();
	return result;
    }

    /* Initialize the control register, turning on interrupts. */
    outb (SP_CR_IRQ | SP_CR_SELECT | SP_CR_INIT, shortp_base + SP_CONTROL);

    return 0;
}

void shortp_cleanup(void)
{
    /* Return the IRQ if we have one */
    if (shortp_irq >= 0) {
        outb(0x0, shortp_base + SP_CONTROL);   /* disable the interrupt */
        free_irq(shortp_irq, NULL);
    }

    /* Don't leave any timers floating around.  Note that any active output
       is effectively stopped by turning off the interrupt */
    if (shortp_output_active)
        del_timer_sync (&shortp_timer);

    /* All done with the device */
    unregister_chrdev(major, "shortprint");
    release_region(shortp_base,SHORTP_NR_PORTS);

    if (shortp_in_buffer) free_page(shortp_in_buffer);
}

module_init(shortp_init);
module_exit(shortp_cleanup);