drv_rs485.c

这是pxa270的RS485驱动程序

/**
* Note:
*    race condition wasn't dealed, if two processes open ad/1 and ad/0, there 
* will be a race condition, we can solve it by add a mutex in struct MagicARM270_AD down the mutex, and then go read
*
*/
#include <asm/io.h>
#include <asm/uaccess.h>
#include <linux/delay.h>
#include <linux/errno.h>    /* error codes */
#include <linux/fs.h>       /* everything... */
#include <linux/kernel.h>   /* printk() */
#include <linux/module.h>
#include <linux/slab.h>     /* kmalloc() */
#include <linux/types.h>    /* size_t */
#include <linux/cdev.h>

#include <asm/arch/hardware.h>
#include <asm/arch/pxa-regs.h>

#include "rs485.h"

#define GPIO_RS485      52		//GP52 as (-RE)/(DE)

static int rs485_major = 0;
static int rs485_minor = 0;

static struct cdev rs485_cdev;

/* Mutual exclusion */
struct semaphore sem;

static void pxa_gpio_set_output(int gpio, int output)
{
    unsigned long flags;
    int _gpio = gpio & 0x7f;        // guarantee _gpio in 0-127

	// following code has been proved right
	if (!!output) {
		GPSR(_gpio) = GPIO_bit(_gpio);
	}else{
		GPCR(_gpio) = GPIO_bit(_gpio);
	}

}

ssize_t rs485_read (struct file *filp, char __user *buf, size_t count,
				 loff_t *f_pos)
{
	return count;
}

int rs485_ioctl (struct inode *inode, struct file *filp, unsigned int cmd, unsigned long arg)
{
    /* don't even decode wrong cmds: better returning  ENOTTY than EFAULT */
    if (_IOC_TYPE(cmd) != RS485_MAGIC)  return -ENOTTY;
    if (_IOC_NR(cmd) > RS485_MAXNR) return -ENOTTY;

	if (!!arg) {
		pxa_gpio_set_output(GPIO_RS485, 1);
	}else{
		pxa_gpio_set_output(GPIO_RS485, 0);
	}

    return 0;
}

struct file_operations fops_rs485 =
{
	.read = rs485_read,
    .ioctl = rs485_ioctl,
};

static void rs485_hw_init(void)
{
    pxa_gpio_mode(GPIO_RS485 | GPIO_OUT);


	pxa_gpio_mode(GPIO46_STRXD_MD);
	pxa_gpio_mode(GPIO47_STTXD_MD);

    printk(KERN_ALERT"Set GPIO 46 and 47 to st_uart\n");

}

static int register_rs485_dev(void)
{
	int ret_alloc_dev = -1; 
	int ret;
    dev_t dev = MKDEV(rs485_major, 0);

    // get dev major and minor
    ret_alloc_dev = alloc_chrdev_region(&dev, 0, 1, "MagicARM270_RS485_CNTL");
    rs485_major = MAJOR(dev);
    rs485_minor = MINOR(dev);
    printk(KERN_ALERT"MagicARM270 RS485 Control Driver Registerd: major=%d, minor=%d\n", rs485_major, rs485_minor);
    printk(KERN_ALERT"use \"mkdir -p /dev/rs485/&& rm -f /dev/rs485/0 && mknod /dev/rs485/0 c %d %d \" to make device node\n", rs485_major, rs485_minor);


    //
    {   int err, devno = MKDEV(rs485_major, rs485_minor);
        // make a char dev
        cdev_init(&rs485_cdev, &fops_rs485);
        rs485_cdev.owner = THIS_MODULE;
        rs485_cdev.ops = &fops_rs485;
        err = cdev_add (&rs485_cdev, devno, 1);
        /* Fail gracefully if need be */
        if (err){
			printk(KERN_ERR "Error Creating char dev");
			return (-1);
		}
    }

	return (0);
}

static int __init rs485_init(void)
{

    rs485_hw_init();

	register_rs485_dev();

    sema_init(&sem, 1);

    return 0;
}

static void __exit rs485_exit(void)
{
    cdev_del(&rs485_cdev);
    unregister_chrdev_region(MKDEV (rs485_major, 0), 1);
}

module_init(rs485_init);
module_exit(rs485_exit);