本文主要是介绍设备树学习之（八）eeprom，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！
开发板：tiny4412SDK + S702 + 4GB Flash
要移植的内核版本：Linux-4.4.0 （支持device tree）
u-boot版本：友善之臂自带的 U-Boot 2010.12
busybox版本：busybox 1.25
目标：
驱动 tiny4412 底板上的 i2c eeprom ，使用字符设备进行读写。
原理图：
设备地址为 0x50
设备树：
&i2c_0{eeprom@50 {//它对应于driverid_table中的namecompatible = "tiny4412,eeprom";reg = <0x50>;};
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代码：
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/platform_device.h>
#include <linux/i2c.h>
#include <linux/err.h>
#include <linux/regmap.h>
#include <linux/slab.h>
#include <linux/fs.h>
#include <asm/uaccess.h>
#include <linux/delay.h>#define uchar unsigned char
#define mydebug() printk("%s %s %d\n", __FILE__, __FUNCTION__, __LINE__)
/*24AA025E482K bit 只有低 1K bit可用因此可以使用的范围 0 - 128 byte一页 16bytes支持写单字节,整页写操作支持单字节读,连续读取
*/static int major;
static struct class *class;
static struct i2c_client *at24cxx_client;/* 传入: buf[0] : addr* 输出: buf[1] : len*/
static ssize_t at24cxx_read(struct file *file, char __user *buf, size_t count, loff_t *off)
{int ret, i;unsigned char addr, len, data[2];unsigned char *readbuf;struct i2c_msg msg[2];if (count != 2){printk("%s count invalid \n", __func__);return -EINVAL;}ret = copy_from_user(data, buf, 2);if (ret < 0){printk("%s copy_from_user error\n", __func__);}addr = data[0];len = data[1];readbuf = kzalloc(len, GFP_KERNEL);if (addr + len - 1 >= 128){printk("%s write addr len invalid \n", __func__);return -EINVAL;}if (len == 0){return 0;}else{readbuf[0] = i2c_smbus_read_byte_data(at24cxx_client, addr);mdelay(20);addr += 1;/* 读AT24CXX时,要先把要读的存储空间的地址发给它 */msg[0].addr = at24cxx_client->addr; /* 目的 */msg[0].buf = &addr; /* 源 */msg[0].len = 1; /* 地址=1 byte */msg[0].flags = 0; /* 表示写 *//* 然后启动读操作 */msg[1].addr = at24cxx_client->addr; /* 源 */msg[1].buf = readbuf + 1; /* 目的 */msg[1].len = len - 1; /* 数据=1 byte */msg[1].flags = I2C_M_RD; /* 表示读 */ret = i2c_transfer(at24cxx_client->adapter, msg, 2);if (ret != 2){printk("%s i2c_transfer error \n", __func__);return -EINVAL;}}if (data < 0){printk("%s data read error\n", __func__);}ret = copy_to_user(buf + 2, readbuf, len);if (ret < 0){printk("%s copy_from_user error\n", __func__);}kfree(readbuf);return count;
}static void calHead(uchar align, uchar start, uchar len, uchar *hstart, uchar *hlen)
{if (start % align + len <= align) //长度很短,不跨段{*hlen = len;*hstart = start;return;}if (start % align == 0) //没有零散头部{*hlen = 0;*hstart = start;}else //有零散头部{//(start % align) 范围 0 - align-1//align - (start % align); 范围 1 - align,start:0 <-> align*hlen = align - (start % align);*hstart = start;}
}static void calMiddle(uchar align, uchar start, uchar len, uchar *mstart, uchar *mlen, uchar *num)
{uchar hstart, hlen;calHead(align, start, len, &hstart, &hlen);*mstart = hstart + hlen;*num = (len - hlen) / align;*mlen = ((len - hlen) / align) * align;
}static void calEnd(uchar align, uchar start, uchar len, uchar *estart, uchar *elen)
{uchar hstart, hlen, mstart, mlen, num;calHead(align, start, len, &hstart, &hlen);calMiddle(align, start, len, &mstart, &mlen, &num);*estart = mstart + mlen;*elen = len - hlen - mlen;
}/* buf[0] : addr_start* buf[1] : len* buf[n] : data*/
static ssize_t at24cxx_write(struct file *file, const char __user *buf, size_t count, loff_t *off)
{int ret, i;unsigned char addr, len;unsigned char pagebuf[17];unsigned char hstart, hlen, mstart, mlen, num, estart, elen;unsigned char *data = kzalloc(count, GFP_KERNEL);struct i2c_msg msg;if (count < 3){printk("%s count invalid \n", __func__);return -EINVAL;}ret = copy_from_user(data, buf, count);if (ret < 0){printk("%s copy_from_user error\n", __func__);}addr = data[0];len = data[1];printk("addr %d len %d\n", addr, len);if (addr + len - 1 >= 128){printk("%s write addr len invalid \n", __func__);return -EINVAL;}calHead( 16, addr, len, &hstart, &hlen);calMiddle(16, addr, len, &mstart, &mlen, &num);calEnd( 16, addr, len, &estart, &elen);for (i = hstart; i < hstart + hlen; i++){if (i2c_smbus_write_byte_data(at24cxx_client, i, data[2 + i - addr]) < 0){printk("%s i2c_smbus_write_byte_data %d \n", __func__, i);return -EINVAL;}mdelay(5);}for (i = mstart; i < mstart + mlen; i += 16){memset(pagebuf, i, 1); //第一个字节为要写入的地址memcpy(pagebuf + 1, data + 2 + i - addr, 16);msg.addr = at24cxx_client->addr; /* 设备地址 */msg.buf = pagebuf; /* 源 */msg.len = 17; /* 地址+数据=17 byte */msg.flags = 0; /* 表示写 */ret = i2c_transfer(at24cxx_client->adapter, &msg, 1);if (ret != 1){printk("%s i2c_transfer error \n", __func__);return -EINVAL;}mdelay(5);}for (i = estart; i < estart + elen; i++){if (i2c_smbus_write_byte_data(at24cxx_client, i, data[2 + i - addr]) < 0){printk("%s i2c_smbus_write_byte_data %d \n", __func__, i);return -EINVAL;}mdelay(5);}kfree(data);return count;
}static struct file_operations at24cxx_fops =
{.owner = THIS_MODULE,.read = at24cxx_read,.write = at24cxx_write,
};static int at24cxx_probe(struct i2c_client *client,const struct i2c_device_id *id)
{at24cxx_client = client;//printk("%s %s %d\n", __FILE__, __FUNCTION__, __LINE__);major = register_chrdev(0, "at24cxx", &at24cxx_fops);class = class_create(THIS_MODULE, "at24cxx");device_create(class, NULL, MKDEV(major, 0), NULL, "at24cxx"); /* /dev/at24cxx */return 0;
}static int at24cxx_remove(struct i2c_client *client)
{//printk("%s %s %d\n", __FILE__, __FUNCTION__, __LINE__);device_destroy(class, MKDEV(major, 0));class_destroy(class);unregister_chrdev(major, "at24cxx");return 0;
}static const struct i2c_device_id at24cxx_id_table[] =
{{ "eeprom", 0 },{}
};/* 1. 分配/设置i2c_driver */
static struct i2c_driver at24cxx_driver =
{.driver = {.name = "eeprom",.owner = THIS_MODULE,},.probe = at24cxx_probe,.remove = at24cxx_remove,.id_table = at24cxx_id_table,
};static int at24cxx_drv_init(void)
{/* 2. 注册i2c_driver */i2c_add_driver(&at24cxx_driver);return 0;
}static void at24cxx_drv_exit(void)
{i2c_del_driver(&at24cxx_driver);
}module_init(at24cxx_drv_init);
module_exit(at24cxx_drv_exit);
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