嵌入式Linux设备驱动程序开发指南15（Linux输入子系统、I2C设备驱动）——读书笔记_linux i2c input

十五、Linux输入子系统、I2C设备驱动

15.1 简介

许多驱动程序不是从一个字符设备开始写的，而是使用固定框架实现，该框架专门针对特定设备类型，如网络设备、串口设备、内存设备）（MTD)、实时时钟、工业IO等。框架的作用是把同类设备驱动程序的公共代码分离出来，以减少代码重复度。框架为每种类型设备提供与驱动无关的一致的用户接口。
驱动如何与框架交互并向用户应用程序，使用硬件资源的功能，如下：

15.2 input_event

输入设备常见的有鼠标、键盘、操作杆、触摸屏等。
输入设备驱动程序统一的格式——input_event数据结构捕获硬件信息，并报告给核心层，核心层对数据进行分类上报事件，最后通过事件层上报给用户态。
输入子系统可分两部分：驱动程序、事件处理程序。
输入子系统划分：event应用程序、输入子系统核心、输入事件驱动、输入轮询设备驱动、I2C驱动；
轮询输入设备头文件定义：

/include/linux/input-polldev.h

struct input_polled_dev;
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input_polled_dev数据结构由poll()回调函数来处理，这个函数轮询设备并产生输入事件。poll()函数内部，驱动程序调用input_event()函数把事件发送到事件处理函数。

15.3设备树

					adxl345@1c {
						compatible = "arrow,adxl345";
						reg = <0x1d>;
					};
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15.4 驱动代码

#include <linux/module.h>
#include <linux/fs.h>
#include <linux/i2c.h>
#include <linux/input-polldev.h>

/* create private structure */
struct ioaccel_dev {
	struct i2c_client * i2c_client;
	struct input_polled_dev * polled_input;
};

#define POWER_CTL	0x2D
#define PCTL_MEASURE	(1 << 3)
#define OUT_X_MSB	0x33

/* poll function */
static void ioaccel_poll(struct input_polled_dev * pl_dev)
{
	struct ioaccel_dev * ioaccel = pl_dev->private;
	int val = 0;
	val = i2c_smbus_read_byte_data(ioaccel->i2c_client, OUT_X_MSB);


	if ( (val > 0xc0) && (val < 0xff) ) {
		input_event(ioaccel->polled_input->input, EV_KEY, KEY_1, 1);
	} else {
		input_event(ioaccel->polled_input->input, EV_KEY, KEY_1, 0);
	}

	input_sync(ioaccel->polled_input->input);
}

static int ioaccel_probe(struct i2c_client * client,
		const struct i2c_device_id * id)
{
	/* declare an instance of the private structure */
	struct ioaccel_dev * ioaccel;
	
	dev_info(&client->dev, "my_probe() function is called.\n");

	/* allocate private structure for new device */
	ioaccel = devm_kzalloc(&client->dev, sizeof(struct ioaccel_dev), GFP_KERNEL);  //声明一个私有数据结构体、并分配空间

	/* associate client->dev with ioaccel private structure */
	i2c_set_clientdata(client, ioaccel);

	/* enter measurement mode */
	i2c_smbus_write_byte_data(client, POWER_CTL, PCTL_MEASURE);

	/* allocate the struct input_polled_dev */
	ioaccel->polled_input = devm_input_allocate_polled_device(&client->dev);

	/* initialize polled input */
	ioaccel->i2c_client = client;
	ioaccel->polled_input->private = ioaccel;

	ioaccel->polled_input->poll_interval = 50;
	ioaccel->polled_input->poll = ioaccel_poll;

	ioaccel->polled_input->input->dev.parent = &client->dev;

	ioaccel->polled_input->input->name = "IOACCEL keyboard";
	ioaccel->polled_input->input->id.bustype = BUS_I2C;

	/* set event types */
	set_bit(EV_KEY, ioaccel->polled_input->input->evbit);
	set_bit(KEY_1, ioaccel->polled_input->input->keybit);

	/* register the device, now the device is global until being unregistered*/
	input_register_polled_device(ioaccel->polled_input);

	return 0;
}

static int ioaccel_remove(struct i2c_client * client)
{
	struct ioaccel_dev * ioaccel;
	ioaccel = i2c_get_clientdata(client);
	input_unregister_polled_device(ioaccel->polled_input);
	dev_info(&client->dev, "ioaccel_remove()\n");
	return 0;
}

/* add entries to device tree */
static const struct of_device_id ioaccel_dt_ids[] = {
	{ .compatible = "arrow,adxl345", },
	{ }
};
MODULE_DEVICE_TABLE(of, ioaccel_dt_ids);

static const struct i2c_device_id i2c_ids[] = {
	{ "adxl345", 0 },
	{ }
};
MODULE_DEVICE_TABLE(i2c, i2c_ids);

/* create struct i2c_driver */
static struct i2c_driver ioaccel_driver = {
	.driver = {
		. = "adxl345",
		.owner = THIS_MODULE,
		.of_match_table = ioaccel_dt_ids,
	},
	.probe = ioaccel_probe,
	.remove = ioaccel_remove,
	.id_table = i2c_ids,
};

/* register to i2c bus as a driver */
module_i2c_driver(ioaccel_driver);  //把驱动程序注册到I2C总线上

MODULE_LICENSE("GPL");
MODULE_AUTHOR(" ");
MODULE_DESCRIPTION("This is an accelerometer INPUT framework platform driver");

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感谢阅读，祝君成功！
-by aiziyou