1, Introduction to MISC driver
MISC driver is actually the simplest character device driver. The master device number of all MISC device drivers is 10. Different devices use different slave device numbers.
MISC device will automatically create cdev, which does not need to be created manually as before. Therefore, using MISC device driver can simplify the writing of character device driver.
We need to register a miscdevice device with Linux. Miscdevice is a structure defined in the file include/linux/miscdevice.h, as follows:
struct miscdevice {
int minor;
const char *name;
const struct file_operations *fops;
struct list_head list;
struct device *parent;
struct device *this_device;
const struct attribute_group **groups;
const char *nodename;
umode_t mode;
};
The main device number of MISC device is 10, which is fixed, and the user needs to specify the sub device number. The Linux system has predefined some sub device numbers of MISC devices, which are defined in the include/linux/miscdevice.h file, as shown below:
/* * These allocations are managed by device@lanana.org. If you use an * entry that is not in assigned your entry may well be moved and * reassigned, or set dynamic if a fixed value is not justified. */ #define PSMOUSE_MINOR 1 #define MS_BUSMOUSE_MINOR 2 /* unused */ #define ATIXL_BUSMOUSE_MINOR 3 /* unused */ /*#define AMIGAMOUSE_MINOR 4 FIXME OBSOLETE */ #define ATARIMOUSE_MINOR 5 /* unused */ #define SUN_MOUSE_MINOR 6 /* unused */ #define APOLLO_MOUSE_MINOR 7 /* unused */ #define PC110PAD_MINOR 9 /* unused */ /*#define ADB_MOUSE_MINOR 10 FIXME OBSOLETE */ #define WATCHDOG_MINOR 130 /* Watchdog timer */ #define TEMP_MINOR 131 /* Temperature Sensor */ #define RTC_MINOR 135 #define EFI_RTC_MINOR 136 /* EFI Time services */ #define VHCI_MINOR 137 #define SUN_OPENPROM_MINOR 139 #define DMAPI_MINOR 140 /* unused */ #define NVRAM_MINOR 144 #define SGI_MMTIMER 153 #define STORE_QUEUE_MINOR 155 /* unused */ #define I2O_MINOR 166 #define MICROCODE_MINOR 184 #define VFIO_MINOR 196 #define TUN_MINOR 200 #define CUSE_MINOR 203 #define MWAVE_MINOR 219 /* ACP/Mwave Modem */ #define MPT_MINOR 220 #define MPT2SAS_MINOR 221 #define MPT3SAS_MINOR 222 #define UINPUT_MINOR 223 #define MISC_MCELOG_MINOR 227 #define HPET_MINOR 228 #define FUSE_MINOR 229 #define KVM_MINOR 232 #define BTRFS_MINOR 234 #define AUTOFS_MINOR 235 #define MAPPER_CTRL_MINOR 236 #define LOOP_CTRL_MINOR 237 #define VHOST_NET_MINOR 238 #define UHID_MINOR 239 #define USERIO_MINOR 240 #define MISC_DYNAMIC_MINOR 255
The name in miscdevice is the name of the MISC device. When the device is registered successfully, a device file named name will be generated in the / dev directory. fops is the operation set of character device. MISC device driver finally needs to use the fops operation set provided by the user.
After setting miscdevice, you need to use misc_register function registers a MISC device in the system. The prototype of this function is as follows:
int misc_register(struct miscdevice * misc)
In the past, we needed to call a bunch of functions to create devices. For example, we used it in the previous character device driver
The following functions complete the device creation process:
1 alloc_chrdev_region(); /* Application equipment No */ 2 cdev_init(); /* Initialize cdev */ 3 cdev_add(); /* Add cdev */ 4 class_create(); /* Create class */ 5 device_create(); /* Create device */
Now we can use misc directly_ Register a function to complete these steps in the above code.
2, MISC driver instance
This driver code is transformed from a previously written led lighting code. We mainly look at misc in the next probe function_ Use of register().
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/errno.h>
#include <linux/miscdevice.h>
#include <linux/kernel.h>
#include <linux/major.h>
#include <linux/mutex.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
#include <linux/stat.h>
#include <linux/init.h>
#include <linux/device.h>
#include <linux/tty.h>
#include <linux/kmod.h>
#include <linux/gfp.h>
#include <linux/gpio/consumer.h>
#include <linux/platform_device.h>
#include <linux/miscdevice.h>
static struct gpio_desc *led_gpio;
#define MISCLED_NAME "miscled" / * name*/
#define MISCLED_MINOR 145
static int led_drv_open(struct inode *node, struct file *file)
{
printk(KERN_INFO "%s %s line is %d \r\n", __FILE__, __FUNCTION__, __LINE__);
gpiod_direction_output(led_gpio, 0);
return 0;
}
static int led_drv_read(struct file *file, char __user *buf, size_t size, loff_t *offset)
{
int status = 0;
int result = 0;
printk(KERN_INFO "%s %s line is %d \r\n", __FILE__, __FUNCTION__, __LINE__);
status = gpiod_get_value(led_gpio);
result = copy_to_user(buf, &status, 1);
return 1;
}
static int led_drv_write(struct file *file, const char __user *buf, size_t size, loff_t *offset)
{
int result;
char status;
printk(KERN_INFO "%s %s line is %d \r\n", __FILE__, __FUNCTION__, __LINE__);
result = copy_from_user(&status, buf, 1);
gpiod_set_value(led_gpio, status);
return 1;
}
static int led_drv_release(struct inode *node, struct file *file)
{
printk(KERN_INFO "%s %s line is %d \r\n", __FILE__, __FUNCTION__, __LINE__);
return 0;
}
/*Facing the sea 0902*/
static struct file_operations led_drv =
{
.owner = THIS_MODULE,
.open = led_drv_open,
.read = led_drv_read,
.write = led_drv_write,
.release = led_drv_release,
};
/* MISC Equipment structure */
static struct miscdevice led_miscdev = {
.minor = MISCLED_MINOR,
.name = MISCLED_NAME,
.fops = &led_drv,
};
static int led_gpio_probe(struct platform_device *pdev)
{
int ret =0;
printk(KERN_INFO "%s %s line is %d \r\n", __FILE__, __FUNCTION__, __LINE__);
led_gpio = gpiod_get(&pdev->dev, "led", 0);
if(IS_ERR(led_gpio))
{
printk(KERN_ERR "gpiod_get is err\r\n");
return -1;
}
ret = misc_register(&led_miscdev);
if(ret < 0)
{
printk("misc device register failed!\r\n");
return -EFAULT;
}
return 0;
}
/*Facing the sea 0902*/
static int led_gpio_remove(struct platform_device *pdev)
{
printk(KERN_INFO "%s %s line is %d \r\n", __FILE__, __FUNCTION__, __LINE__);
misc_deregister(&led_miscdev);
gpiod_put(led_gpio);
return 0;
}
static const struct of_device_id my_led[] =
{
{.compatible = "my,led_driver"},
{},
};
static struct platform_driver led_gpio_driver =
{
.probe = led_gpio_probe,
.remove = led_gpio_remove,
.driver =
{
.name = "led_gpio",
.of_match_table = my_led,
},
};
static int __init led_init(void)
{
int result;
printk(KERN_INFO "%s %s line is %d \r\n", __FILE__, __FUNCTION__, __LINE__);
result = platform_driver_register(&led_gpio_driver);
return result;
}
static void __exit led_exit(void)
{
printk(KERN_INFO "%s %s line is %d \r\n", __FILE__, __FUNCTION__, __LINE__);
platform_driver_unregister(&led_gpio_driver);
}
module_init(led_init);
module_exit(led_exit);
MODULE_LICENSE("GPL");
/*Facing the sea 0902*/
After the driver is loaded, we see a device named "miscled" under the / dev directory. The main device number is 10 and the device number is 145, which is consistent with our code.
3, MISC example test
Write a simple test program, write() and read() device nodes, and then trigger the driver fops file operation function.
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>
/*
* ./ledtest /dev/miscled on
* ./ledtest /dev/miscled off
*/
int main(int argc, char **argv)
{
int fd;
char status;
/* 1. Judgment parameters */
if (argc != 3)
{
printf("Usage: %s <dev> <on | off>\n", argv[0]);
return -1;
}
/* 2. Open file */
fd = open(argv[1], O_RDWR | O_NONBLOCK);
if (fd == -1)
{
printf("can not open file %s\n", argv[1]);
return -1;
}
/* 3. Write file */
if (0 == strcmp(argv[2], "on"))
{
status = 1;
write(fd, &status, 1);
}
else
{
status = 0;
write(fd, &status, 1);
}
read(fd, &status, 1);
printf("status is %d\n", status);
close(fd);
return 0;
}
Test on the development board and print as follows:
[root@Joy:/dev]# /mnt/misc_test /dev/miscled on [ 1133.332943] /home/book/code/test/misc_drv.c led_drv_open line is 27 [ 1133.340139] /home/book/code/test/misc_drv.c led_drv_write line is 46 [ 1133.352154] /home/book/code/test/misc_drv.c led_drv_read line is 36 status is 1 [ 1133.360455] /home/book/code/test/misc_drv.c led_drv_release line is 54 [root@100ask:/dev]# /mnt/misc_test /dev/miscled off [ 1146.420773] /home/book/code/test/misc_drv.c led_drv_open line is 27 [ 1146.428629] /home/book/code/test/misc_drv.c led_drv_write line is 46 [ 1146.436893] /home/book/code/test/misc_drv.c led_drv_read line is 36 status is 0 [ 1146.445773] /home/book/code/test/misc_drv.c led_drv_release line is 54 /*Facing the sea 0902*/