/*
* 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 2004/09/26 08:01:04 gregkh Exp $
*/
#include <linux/config.h>
#include <linux/module.h>
#include <linux/moduleparam.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/slab.h>
#include <linux/ioport.h>
#include <linux/interrupt.h>
#include <linux/workqueue.h>
#include <linux/timer.h>
#include <linux/poll.h>
#include <asm/io.h>
#include <asm/semaphore.h>
#include <asm/atomic.h>
#include "shortprint.h"
#define SHORTP_NR_PORTS 3
//接受默认值或者从命令行接收
/*
* 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_param(major, int, 0);
/* 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_param(base, long, 0);
/* The interrupt line is undefined by default. "shortp_irq" is as above */
static int irq = -1;
static int shortp_irq = -1;
module_param(irq, int, 0);
/* Microsecond delay around strobe. */
static int delay = 0;
static int shortp_delay;
module_param(delay, int, 0);
MODULE_AUTHOR ("Jonathan Corbet");
MODULE_LICENSE("Dual BSD/GPL");
/*
* Forwards.
*/
static void shortp_cleanup(void);
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); //初始化输入的等待队列
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.
*/
static unsigned char *shortp_out_buffer = NULL;
static volatile unsigned char *shortp_out_head, *shortp_out_tail;
static struct semaphore shortp_out_sem;
static DECLARE_WAIT_QUEUE_HEAD(shortp_out_queue);//初始化输出的等待队列
/*
* Feeding the output queue to the device is handled by way of a
* workqueue.
*/
static void shortp_do_work(void *);
static DECLARE_WORK(shortp_work, shortp_do_work, NULL); //声明一个工作执行shortp_do_work函数，参数null
static struct workqueue_struct *shortp_workqueue; //工作队列
/*
* 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(void)
{
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 *///初始化释放的等待队列。因为该等待队列只有在释放设备的时候压入程序
/*
* 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.
*/
static int shortp_open(struct inode *inode, struct file *filp)
{
return 0;
}
static 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);
return 0;
}
static unsigned int shortp_poll(struct file *filp, poll_table *wait)
{
return POLLIN | POLLRDNORM | POLLOUT | POLLWRNORM;
}
/*
* The read routine, which doesn't return data from the device; instead, it
* returns timing information just like the "short" device.
*/
static ssize_t shortp_read(struct file *filp, char __user *buf, size_t count, loff_t *f_pos)
{
int count0;
DEFINE_WAIT(wait);//建立等待队列入口
while (shortp_in_head == shortp_in_tail) {
prepare_to_wait(&shortp_in_queue, &wait, TASK_INTERRUPTIBLE);//等待队列头添加入队列
if (shortp_in_head == shortp_in_tail)
schedule();//让出cpu
finish_wait(&shortp_in_queue, &wait); //休眠结束，清理函数
if (signal_pending (current)) /* a signal arrived */
return -ERESTARTSYS; /* tell the fs layer to handle it */
}
/* count0 is the number of readable data bytes */
count0 = shortp_in_head - shortp_in_tail;
if (count0 < 0) /* wrapped */
//若尾指针在头指针前面，说明写入的信息写完了整个缓存区从头开始写了
//则打印出头指针到缓存末的字符个数
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);//将索引向前移动count个
return count;
}
/*
* Wait for the printer to be ready; this can sleep.
等待打印机可以工作
*/
static void shortp_wait(void)
{
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);
}
}
}
/*
* 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(void)
{
unsigned char cr = inb(shortp_base + SP_CONTROL);
/* Something happened; reset the timer */
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);
}
/*
* Start output; call under lock.
*/
static void shortp_start_output(void)
{
if (shortp_output_active) /* Should never happen */
return;
/* Set up our 'missed interrupt' timer */
shortp_output_active = 1;
shortp_timer.expires = jiffies + TIMEOUT;
add_timer(&shortp_timer);
/* And get the process going. */
queue_work(shortp_workqueue, &shortp_work);
}
/*
* Write to the device.
*/
static ssize_t shortp_write(struct file *filp, const char __user *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))
//若没有空间，添加到等待队列等待有空间的条件成立且wake被唤醒
goto out;
}
/* 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. */
//若没有输出设备激活，激活并设置定时器。
spin_lock_irqsave(&shortp_out_lock, flags);
if (! shortp_output_active)
shortp_start_output();
spin_unlock_irqrestore(&shortp_out_lock, flags);
}
out:
*f_pos += written;
up(&shortp_out_sem);
return written;
}
/*
* The bottom-half handler.
*/
static void shortp_do_work(void *unused)
{
int written;
unsigned long flags;
/* Wait until the device is ready */
shortp_wait();
spin_lock_irqsave(&shortp_out_lock, flags);
/* Have we written everything? */
if (shortp_out_head == shortp_out_tail) { /* empty */
shortp_output_active = 0;
wake_up_interruptible(&shortp_empty_queue);
del_timer(&shortp_timer);
}
/* Nope, write another byte */
else
shortp_do_write();
/* If somebody's waiting, maybe 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.
*/
static irqreturn_t shortp_interrupt(int irq, void *dev_id, struct pt_regs *regs)
{
if (! shortp_output_active)
return IRQ_NONE;
/* Remember the time, and farm off the rest to the workqueue function */
do_gettimeofday(&shortp_tv);
queue_work(shortp_workqueue, &shortp_work);//把工作shortp_work添加到工作队列里
return IRQ_HANDLED;
}
/*
* 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;
if (! shortp_output_active)
return;
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);
}
static struct file_operations shortp_fops = {
.read = shortp_read,
.write = shortp_write,
.open = shortp_open,
.release = shortp_release,
.poll = shortp_poll,
.owner = THIS_MODULE
};
/*
* Module initialization
*/
static 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;
/* Get our needed resources. */
//分配IO端口
if (! request_region(shortp_base, SHORTP_NR_PORTS, "shortprint")) {
printk(KERN_INFO "shortprint: can't get I/O port address 0x%lx\n",
shortp_base);
return -ENODEV;
}
/* Register the device */
//注册设备
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 */
//开辟输入输出的内存
/* 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;//设置定时器函数
shortp_timer.data = 0;
/* Set up our workqueue. */
//创建单线程工作的工作队列
shortp_workqueue = create_singlethread_workqueue("shortprint");
/* 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. */
//直接IO输出，启动中断，初始化控制控制寄存器
outb(SP_CR_IRQ | SP_CR_SELECT | SP_CR_INIT, shortp_base + SP_CONTROL);
return 0;
}
static 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);
}
/* All done with the device */
unregister_chrdev(major, "shortprint");
release_region(shortp_base,SHORTP_NR_PORTS);
/* 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);
flush_workqueue(shortp_workqueue);
destroy_workqueue(shortp_workqueue);
if (shortp_in_buffer)
free_page(shortp_in_buffer);
if (shortp_out_buffer)
free_page((unsigned long) shortp_out_buffer);
}
module_init(shortp_init);
module_exit(shortp_cleanup);
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