I2C是一种重要的通信协议，因为他只有两根信号线(时钟线SCL/数据线SDA)，而且采用OC门外接电路，所以它兼具了两个优点：布线简单；可外接多个从设备。
对于I2C的通信协议网上介绍的已经很多，仔细阅读的话都可以很容易的理解透彻，而且可以在普通的MCU上很容易的通过配置寄存器，甚至是采用IO模拟使用起来，但是如果把I2C放在Linux系统中又是什么样的呢？这里介绍下小白的经历。
当前在调试android的屏幕显示问题，因为采用的是双屏，而soc中屏幕接口(lvds/RGB)又是复用的，所以这里采用MIPI转成了lvds，然后外接lvds屏幕（至于为什么要采用lvds屏，也是因为之前项目中的后遗症），这个转换芯片就是icn6201，这时就需要采用某种方式对icn6201转换芯片进行配置，icn6201支持dsi和i2c两种接口进行配置，我们轻易的就选择了i2c配置(没有任何理由？)。
因为这里只是在开机时对转换芯片进行下配置，不需要衔接android内部的其他接口，所以我就打算直接写个驱动来进行操作就行了。
这里时添加驱动的操作：
+++ ./drivers/i2c/Makefile 2017-04-13 13:20:16.000000000 +0800
@@ -6,6 +6,7 @@
obj-$(CONFIG_I2C) += i2c-core.o
obj-$(CONFIG_I2C_SMBUS) += i2c-smbus.o
obj-$(CONFIG_I2C_CHARDEV) += i2c-dev.o
+obj-$(CONFIG_I2C_INIT_ICN6201) += icn6201.o
obj-$(CONFIG_I2C_MUX) += i2c-mux.o
obj-y += algos/ busses/ muxes/
obj-$(CONFIG_I2C_STUB) += i2c-stub.o
+++ ./drivers/i2c/Kconfig 2017-04-17 22:24:22.365686411 +0800
@@ -46,6 +46,13 @@
This support is also available as a module. If so, the module
will be called i2c-dev.
+config I2C_INIT_ICN6201
+ tristate "i2c init icn6201"
+ default M
+ help
+ i2c init icn6201
+
+
config I2C_MUX
tristate "I2C bus multiplexing support"
depends on HAS_IOMEM
接下来就是添加驱动文件driver/i2c/icn6201.c了：
+++ ./drivers/i2c/icn6201.c 2017-04-17 22:35:17.658101099 +0800
@@ -0,0 +1,368 @@
+/*
+ icn6201.c - init icn6201 for screen 10.1
+*/
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/device.h>
+#include <linux/notifier.h>
+#include <linux/fs.h>
+#include <linux/slab.h>
+#include <linux/init.h>
+#include <linux/list.h>
+#include <linux/i2c.h>
+#include <linux/i2c-dev.h>
+#include <linux/jiffies.h>
+#include <linux/uaccess.h>
+
+/*
+ * An i2c_dev represents an i2c_adapter ... an I2C or SMBus master, not a
+ * slave (i2c_client) with which messages will be exchanged. It's coupled
+ * with a character special file which is accessed by user mode drivers.
+ *
+ * The list of i2c_dev structures is parallel to the i2c_adapter lists
+ * maintained by the driver model, and is updated using bus notifications.
+ */
+struct i2c_dev {
+ struct list_head list;
+ struct i2c_adapter *adap;
+ struct device *dev;
+};
+
+struct icn6201_data {
+ struct i2c_client *icn6201_client;
+};
+
+static int icn6201_smbus_write_byte(struct i2c_client *client, unsigned char reg_addr, unsigned char *data)
+{
+ s32 dummy;
+ dummy = i2c_smbus_write_byte_data(client, reg_addr, *data);
+ if (dummy < 0){
+ printk("icn6201_smbus_write_byte: write byte data failed\n");
+ return -1;
+ }
+ printk("icn6201_smbus_write_byte: write data successful!\n");
+ return 0;
+}
+
+// static int icn6201_smbus_read_byte(struct i2c_client *client, unsigned char reg_addr, unsigned char *data)
+// {
+// s32 dummy;
+// dummy = i2c_smbus_read_byte_data(client, reg_addr, *data);
+// if (dummy < 0){
+// printk("icn6201_smbus_read_byte: read byte data failed\n");
+// return -1;
+// }
+// printk("icn6201_smbus_read_byte: read data successful!\n");
+// return 0;
+// }
+
+#define BIST_MODE
+static int icn6201_probe(struct i2c_client *client, const struct i2c_device_id *id)
+{
+ int err = 0, i = 0;
+ struct icn6201_data *data;
+ unsigned char tmp_value = 0;
+
+ unsigned char addr_value[][2] = {
+#ifdef BIST_MODE
+ {0x20, 0x00}, {0x21, 0x20}, {0x22, 0x35},
+ {0x23, 0x55}, {0x24, 0x28}, {0x25, 0xA8},
+ {0x26, 0x00}, {0x27, 0x0A}, {0x28, 0x06},
+ {0x29, 0x10},
+
+ {0x34, 0x80}, {0x36, 0x55}, {0xB5, 0xA0},
+ {0x5C, 0xFF}, {0x56, 0x90}, {0x6B, 0x21},
+ {0x69, 0x26}, {0x10, 0x47}, {0x2A, 0x41},
+ {0xB6, 0x20}, {0x51, 0x20}, {0x09, 0x10},
+#endif
+ };
+ printk("icn6201:=============Probe==================\n");
+
+ if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C)){
+ dev_err(&client->dev, "System need I2C function.\n");
+ return err;
+ }
+
+ // 这里也申请了i2c_client的空间，相当于实例化
+ data = kzalloc(sizeof(struct icn6201_data), GFP_KERNEL);
+ if (!data) {
+ return -ENOMEM;
+ }
+
+ i2c_set_clientdata(client, data);
+ data->icn6201_client = client;
+
+ for(i=0; i<sizeof(addr_value)/2; i++){
+ printk("icn6201: write data:%X to addr:%X\n", addr_value[i][1], addr_value[i][0]);
+ icn6201_smbus_write_byte(client, addr_value[i][0], &addr_value[i][1]);
+ // icn6201_smbus_read_byte(client, addr_value[i][0], &addr_value[i][1]);
+ printk("icn6201: read data:%X to addr:%X\n", addr_value[i][1], addr_value[i][0]);
+ }
+
+ return 0;
+}
+
+static int icn6201_remove(struct i2c_client *client)
+{
+ return 0;
+}
+
+static const struct i2c_device_id icn6201_id[] = {
+ { "icn6201", 0 },
+ {}
+};
+MODULE_DEVICE_TABLE(i2c, icn6201_id);
+
+int icn6201_detect(struct i2c_client *client, struct i2c_board_info *info)
+{
+ // 这里是获取总线信息，然后进行判断
+ return 0;
+}
+
+static const unsigned short normal_i2c[2] = {0x58>>1, I2C_CLIENT_END, };
+
+static struct i2c_board_info icn6201_board_info = {
+ .type = "icn6201",
+ .addr = 0x58>>1,
+ // {I2C_BOARD_INFO("icn6201", 0x58>>1),},
+};
+
+// 每一个I2C设备驱动，必须首先创造一个i2c_driver结构体对象
+static struct i2c_driver icn6201_driver = {
+ .class = I2C_CLASS_HWMON,
+ .probe = icn6201_probe,
+ .remove = icn6201_remove,
+ .id_table = icn6201_id,
+ .driver = {
+ .name = "icn6201",
+ .owner = THIS_MODULE,
+ },
+ .detect = icn6201_detect,
+ .address_list = normal_i2c,
+};
+
+// static void print_i2c_list()
+// {
+//
+// }
+
+static struct i2c_client *local_client = NULL;
+
+static int __init icn6201_init(void)
+{
+ int ret;
+ struct i2c_adapter *i2c_adap;
+
+ i2c_adap = i2c_get_adapter(0);
+ local_client = i2c_new_device(i2c_adap, &icn6201_board_info);
+ i2c_put_adapter(i2c_adap);
+
+ printk("icn6201_init: i2c to init icn6201 driver\n");
+ ret = i2c_add_driver(&icn6201_driver);
+ if(ret)
+ printk("icn6201_init: i2c_add_driver err");
+
+ // i2c_register_board_info(0, icn6201_board_info, ARRAY_SIZE(icn6201_board_info));
+
+ return ret;
+}
+
+static void __exit icn6201_exit(void)
+{
+ printk("icn6201_exit: i2c to del icn6201 driver\n");
+ i2c_unregister_device(local_client);
+ i2c_del_driver(&icn6201_driver);
+}
+
+MODULE_AUTHOR("Frodo Looijaard <frodol@dds.nl> and "
+ "Simon G. Vogl <simon@tk.uni-linz.ac.at>");
+MODULE_DESCRIPTION("I2C /dev entries driver");
+MODULE_LICENSE("GPL");
+
+module_init(icn6201_init);
+module_exit(icn6201_exit);