Table of contents
1. Modify the device tree (the device tree is used to specify pin resources)
1. Modify the device tree (the device tree is used to specify pin resources)
- Place it under which I2C controller
- I2C device address of AT24C02 (check chip manual 0x50)
- compatible attribute: used to address the driver
Modify the device tree: vi arch/arm/boot/dts/100ask_imx6ull-14x14.dts in the kernel directory
&i2c1 {
clock-frequency = <100000>;
pinctrl-names = "default";
pinctrl-0 = <&pinctrl_i2c1>;
status = "okay";
at24c02 {
compatible = "100ask,i2cdev";
reg = <0x50>;//设备地址 查看芯片手册
};
};
The at24c02 node will be converted into i2c_client. There is an adpater in i2c_client, i2c_client.adpater. i2c_client.adpater will point to an i2c controller. The i2c controller corresponds to the &i2c1 node, that is, &i2c1 is an i2c controller. The driver for the i2c controller &i2c1 has been written in the kernel.
2. Write the driver
Modify the i2c_drv_read and i2c_drv_write functions based on the I2C driver framework
2.1 i2c_drv_read
To read the 0 address data of AT24C02, you need to complete the following steps:
-
Initialize i2c_msg
-
Initiate a write operation: send 0 to AT24C02, indicating that data is to be read from address 0
-
Initiate a read operation: get data
/* 实现对应的open/read/write等函数，填入file_operations结构体 */
static ssize_t i2c_drv_read (struct file *file, char __user *buf, size_t size, loff_t *offset)
{
int err;
unsigned char *kern_buf;
struct i2c_msg msgs[2];
/* 从0读取size字节 */
kern_buf = kmalloc(size, GFP_KERNEL);
/* 初始化i2c_msg
* 1. 发起一次写操作: 把0发给AT24C02, 表示要从0地址读数据
* 2. 发起一次读操作: 得到数据
*/
msgs[0].addr = g_client->addr; //设备树里记录了设备地址：0x50
msgs[0].flags = 0; //flags为0：写操作
msgs[0].buf = kern_buf; //取得数据
kern_buf[0] = 0; //buf里第一个字节表示设备存储空间地址，把地址数据0发给设备
msgs[0].len = 1; //发送长度为1，即 发送一个字节数据0给设备
msgs[1].addr = g_client->addr;
msgs[1].flags = I2C_M_RD; //读操作
msgs[1].buf = kern_buf; //读到的数据保存在kern_buf里
msgs[1].len = size; //读size个数据
//函数由内核提供
err = i2c_transfer(g_client->adapter, msgs, 2);
/* copy_to_user */
err = copy_to_user(buf, kern_buf, size);
kfree(kern_buf);
return size;
}2.2 i2c_drv_write
AT24C02 only has 8 bytes of memory in one page, so writing multiple data requires cyclic writing.
To realize reading data starting from address 0 of AT24C02, you need to complete the following steps:
-
Initialize i2c_msg
-
Initiate a write operation: send the address to AT24C02, indicating that you want to read data from the address
-
Address offset and continue writing
//一页只有8个字节 循环写
static ssize_t i2c_drv_write(struct file *file, const char __user *buf, size_t size, loff_t *offset)
{
int err;
unsigned char kern_buf[9];
struct i2c_msg msgs[1];
int len;
unsigned char addr = 0;
/* 把size字节的数据写入地址0 */
//kern_buf = kmalloc(size+1, GFP_KERNEL);
while (size > 0)
{
if (size > 8)
len = 8;
else
len = size;
size -= len;
/* copy_from_user */
err = copy_from_user(kern_buf+1, buf, len);
buf += len;
/* 初始化i2c_msg
* 1. 发起一次写操作: 把0发给AT24C02, 表示要从0地址读数据
* 2. 发起一次读操作: 得到数据
*/
msgs[0].addr = g_client->addr;
msgs[0].flags = 0; /* 写操作 */
msgs[0].buf = kern_buf;
kern_buf[0] = addr; // 写AT24C02的地址，从0开始写，buf里第一个字节表示设备存储空间地址
msgs[0].len = len+1;
addr += len;
err = i2c_transfer(g_client->adapter, msgs, 1);
mdelay(20);//写一页需要时间约10ms，烧写一页数据需等待
}
//kfree(kern_buf);
return size;
}2.3 Complete driver
i2c_drv.c
#include "asm/uaccess.h"
#include "linux/delay.h"
#include "linux/i2c.h"
#include <linux/module.h>
#include <linux/poll.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/of_gpio.h>
#include <linux/of_irq.h>
#include <linux/interrupt.h>
#include <linux/irq.h>
#include <linux/slab.h>
#include <linux/fcntl.h>
#include <linux/timer.h>
/* 主设备号 */
static int major = 0;
static struct class *my_i2c_class;
static struct i2c_client *g_client;
static DECLARE_WAIT_QUEUE_HEAD(gpio_wait);
struct fasync_struct *i2c_fasync;
/* 实现对应的open/read/write等函数，填入file_operations结构体 */
static ssize_t i2c_drv_read (struct file *file, char __user *buf, size_t size, loff_t *offset)
{
int err;
unsigned char *kern_buf;
struct i2c_msg msgs[2];
/* 从0读取size字节 */
kern_buf = kmalloc(size, GFP_KERNEL);
/* 初始化i2c_msg
* 1. 发起一次写操作: 把0发给AT24C02, 表示要从0地址读数据
* 2. 发起一次读操作: 得到数据
*/
msgs[0].addr = g_client->addr; //设备树里记录了设备地址：0x50
msgs[0].flags = 0; //flags为0：写操作
msgs[0].buf = kern_buf; //取得数据
kern_buf[0] = 0; //buf里第一个字节表示设备存储空间地址，把地址数据0发给设备
msgs[0].len = 1; //发送长度为1，即 发送一个字节数据0给设备
msgs[1].addr = g_client->addr;
msgs[1].flags = I2C_M_RD; //读操作
msgs[1].buf = kern_buf; //读到的数据保存在kern_buf里
msgs[1].len = size; //读size个数据
//函数由内核提供
err = i2c_transfer(g_client->adapter, msgs, 2);
/* copy_to_user */
err = copy_to_user(buf, kern_buf, size);
kfree(kern_buf);
return size;
}
//一页只有8个字节 循环写
static ssize_t i2c_drv_write(struct file *file, const char __user *buf, size_t size, loff_t *offset)
{
int err;
unsigned char kern_buf[9];
struct i2c_msg msgs[1];
int len;
unsigned char addr = 0;
/* 把size字节的数据写入地址0 */
//kern_buf = kmalloc(size+1, GFP_KERNEL);
while (size > 0)
{
if (size > 8)
len = 8;
else
len = size;
size -= len;
/* copy_from_user */
err = copy_from_user(kern_buf+1, buf, len);
buf += len;
/* 初始化i2c_msg
* 1. 发起一次写操作: 把0发给AT24C02, 表示要从0地址读数据
* 2. 发起一次读操作: 得到数据
*/
msgs[0].addr = g_client->addr;
msgs[0].flags = 0; /* 写操作 */
msgs[0].buf = kern_buf;
kern_buf[0] = addr; // 写AT24C02的地址，从0开始写，buf里第一个字节表示设备存储空间地址
msgs[0].len = len+1;
addr += len;
err = i2c_transfer(g_client->adapter, msgs, 1);
mdelay(20);//写一页需要时间约10ms，烧写一页数据需等待
}
//kfree(kern_buf);
return size;
}
static unsigned int i2c_drv_poll(struct file *fp, poll_table * wait)
{
//printk("%s %s line %d\n", __FILE__, __FUNCTION__, __LINE__);
poll_wait(fp, &gpio_wait, wait);
//return is_key_buf_empty() ? 0 : POLLIN | POLLRDNORM;
return 0;
}
static int i2c_drv_fasync(int fd, struct file *file, int on)
{
if (fasync_helper(fd, file, on, &i2c_fasync) >= 0)
return 0;
else
return -EIO;
}
/* 定义自己的file_operations结构体 */
static struct file_operations i2c_drv_fops = {
.owner = THIS_MODULE,
.read = i2c_drv_read,
.write = i2c_drv_write,
.poll = i2c_drv_poll,
.fasync = i2c_drv_fasync,
};
static int i2c_drv_probe(struct i2c_client *client,
const struct i2c_device_id *id)
{
// struct device_node *np = client->dev.of_node;
// struct i2c_adapter *adapter = client->adapter;
/* 记录client */
g_client = client;
/* 注册字符设备 */
/* 注册file_operations */
major = register_chrdev(0, "100ask_i2c", &i2c_drv_fops); /* /dev/gpio_desc */
my_i2c_class = class_create(THIS_MODULE, "100ask_i2c_class");
if (IS_ERR(my_i2c_class)) {
printk("%s %s line %d\n", __FILE__, __FUNCTION__, __LINE__);
unregister_chrdev(major, "100ask_i2c");
return PTR_ERR(my_i2c_class);
}
device_create(my_i2c_class, NULL, MKDEV(major, 0), NULL, "myi2c"); /* /dev/myi2c */
return 0;
}
static int i2c_drv_remove(struct i2c_client *client)
{
/* 反注册字符设备 */
device_destroy(my_i2c_class, MKDEV(major, 0));
class_destroy(my_i2c_class);
unregister_chrdev(major, "100ask_i2c");
return 0;
}
static const struct of_device_id myi2c_dt_match[] = {
{ .compatible = "100ask,i2cdev" },
{},
};
//必须有这个，不然装载驱动不成功
static const struct i2c_device_id at24c02_ids[] = {
{ "xxxxyyy", (kernel_ulong_t)NULL },
{ /* END OF LIST */ }
};
static struct i2c_driver my_i2c_driver = {
.driver = {
.name = "100ask_i2c_drv",
.owner = THIS_MODULE,
.of_match_table = myi2c_dt_match,
},
.probe = i2c_drv_probe,
.remove = i2c_drv_remove,
.id_table = at24c02_ids,
};
static int __init i2c_drv_init(void)
{
/* 注册i2c_driver */
return i2c_add_driver(&my_i2c_driver);
}
static void __exit i2c_drv_exit(void)
{
/* 反注册i2c_driver */
i2c_del_driver(&my_i2c_driver);
}
/* 7. 其他完善：提供设备信息，自动创建设备节点 */
module_init(i2c_drv_init);
module_exit(i2c_drv_exit);
MODULE_LICENSE("GPL");
3. Computer test
- Recompile the device tree in the /home/book/100ask_imx6ull-sdk/Linux-4.9.88 directory: make dtbs
- Copy it to the board as follows:
PC:
cp arch/arm/boot/dts/100ask_imx6ull-14x14.dtb ~/nfs_rootfs/
开发板:
mount -t nfs -o nolock,vers=3 192.168.5.11:/home/book/nfs_rootfs /mnt
cp /mnt/100ask_imx6ull-14x14.dtb /boot
reboot
- Enter the system firmware directory and view cd /sys/firmware/devicetree/base/
- Check whether there is this device under the system bus i2c device
There is this device, but there is no corresponding driver
- Mount the network file system: mount -t nfs -o nolock,vers=3 192.168.5.11:/home/book/nfs_rootfs /mnt
- Load driver: insmod i2c_drv.ko
- View the corresponding device node: ls /dev/myi2c -l
- View usage, test driver
Data read successfully!