本篇记录在友善之臂 mini2440 平台上挂载I2C接口触摸屏的驱动开发过程。

内核版本linux-2.6.32.2,
平台是ARM9 S3C2440+I2C接口的触摸屏

如上篇 Linux的I2C驱动体系结构讲述
http://www.lupaworld.com/273398/viewspace-204237.html

要挂载新的I2C设备，需要实现3部分：

1) 适配器的硬件驱动：
内核中已经实现mini2440,i2c适配器驱动，可以在如下目录i2c-s3c2410.c中看到相关代码
linux-2.6.32.2/drivers/i2c/busses/i2c-s3c2410.c

2) I2C 设配器的algorithm
同样在inux-2.6.32.2/drivers/i2c/busses/i2c-s3c2410.c文件中实现。

以上两部分无须做任何更改

3) I2C设备驱动，可以以linux-2.6.32.2/drivers/input/touchscreen/migor_ts.c为例，分析如下：
//-------------------------------------------------------------------//
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/input.h>
#include <linux/interrupt.h>
#include <asm/io.h>
#include <linux/i2c.h>
#include <linux/timer.h>
#include <linux/delay.h>

/*resolution definion according to touch screen */
#define MIN_X_COORDINATE    0
#define MAX_X_COORDINATE    1024   
#define MIN_Y_COORDINATE    0
#define MAX_Y_COORDINATE    768

/* touch screen data structure */
struct i2c_ts_priv {
    struct i2c_client *client;
    struct input_dev *input;
    struct delayed_work work;
    int irq;
};

static void i2c_ts_poscheck(struct work_struct *work)
{
    struct i2c_ts_priv *priv = container_of(work, struct i2c_ts_priv, work.work);
    /* buffer for storing data */
    char buf[6];
    int number;
    int xpos, ypos;

    memset(buf, 0, sizeof(buf));

    /* Now do Page Read */
    if (i2c_master_recv(priv->client, buf,6) != 6) {
        dev_err(&priv->client->dev, "Unable to read i2c page\n");
        goto out;
    }
       
    /* convert coordinate */
    number = buf[0]&0x07;
    xpos = ((buf[3] << 8) | buf[2]);
    ypos = ((buf[5] << 8) | buf[4]);
   
     /* report input event */
    if ((number != 0) && (xpos != 0) && (ypos != 0)) {
        input_report_key(priv->input, BTN_TOUCH, 1);
        input_report_abs(priv->input, ABS_X, xpos);
        input_report_abs(priv->input, ABS_Y, ypos);
        input_sync(priv->input);
    } else if (number == 0) {
        input_report_key(priv->input, BTN_TOUCH, 0);
        input_sync(priv->input);
    }

 out:
    enable_irq(priv->irq);
}

/* read finger numbers and coordinate and report input event */
static irqreturn_t i2c_ts_isr(int irq, void *dev_id)
{
    struct i2c_ts_priv *priv = dev_id;
      
    /* disable irq */
    disable_irq_nosync(irq);
    schedule_delayed_work(&priv->work, HZ/100);   
    return IRQ_HANDLED;
}


static int i2c_ts_open(struct input_dev *dev)
{
    return 0;
}

static void i2c_ts_close(struct input_dev *dev)
{

}

static int i2c_ts_probe(struct i2c_client *client,
              const struct i2c_device_id *idp)
{
    struct i2c_ts_priv *priv;
    struct input_dev *input;
    int error;
    char buf[2];   

    priv = kzalloc(sizeof(*priv), GFP_KERNEL);
    if (!priv) {
        dev_err(&client->dev, "failed to allocate driver data\n");
        error = -ENOMEM;
        goto err0;
    }

    dev_set_drvdata(&client->dev, priv);

    input = input_allocate_device();
    if (!input) {
        dev_err(&client->dev, "Failed to allocate input device.\n");
        error = -ENOMEM;
        goto err1;
    }

    input->evbit[0] = BIT_MASK(EV_KEY) | BIT_MASK(EV_ABS);
    input->keybit[BIT_WORD(BTN_TOUCH)] = BIT_MASK(BTN_TOUCH);

    input_set_abs_params(input, ABS_X, MIN_X_COORDINATE, MAX_X_COORDINATE, 0, 0);
    input_set_abs_params(input, ABS_Y, MIN_Y_COORDINATE, MAX_Y_COORDINATE, 0, 0);

    input->name = client->name;
    input->id.bustype = BUS_I2C;
    input->dev.parent = &client->dev;

    input->open = i2c_ts_open;
    input->close = i2c_ts_close;

    input_set_drvdata(input, priv);

    priv->client = client;
    priv->input = input;
    INIT_DELAYED_WORK(&priv->work, i2c_ts_poscheck);
    priv->irq = client->irq;

    error = input_register_device(input);
    if (error)
        goto err1;

    error = request_irq(priv->irq, i2c_ts_isr, IRQF_TRIGGER_FALLING,
                client->name, priv);
    if (error) {
        dev_err(&client->dev, "Unable to request touchscreen IRQ.\n");
        goto err2;
    }

    device_init_wakeup(&client->dev,1);
   
    return 0;

 err2:
    input_unregister_device(input);
    input = NULL; /* so we dont try to free it below */
 err1:
    input_free_device(input);
    kfree(priv);
 err0:
    dev_set_drvdata(&client->dev, NULL);
    return error;
}

static int i2c_ts_remove(struct i2c_client *client)
{
    struct i2c_ts_priv *priv = dev_get_drvdata(&client->dev);

    free_irq(priv->irq, priv);
    input_unregister_device(priv->input);
    kfree(priv);

    dev_set_drvdata(&client->dev, NULL);

    return 0;
}

static int i2c_ts_suspend(struct i2c_client *client, pm_message_t mesg)
{
    struct i2c_ts_priv *priv = dev_get_drvdata(&client->dev);
    if(device_may_wakeup(&client->dev))
    enable_irq_wake(priv->irq);
    return 0;
}

static int i2c_ts_resume(struct i2c_client *client)
{
    struct i2c_ts_priv *priv = dev_get_drvdata(&client->dev);
    if(device_may_wakeup(&client->dev))
    disable_irq_wake(priv->irq);
    return 0;
}

static const struct i2c_device_id i2c_ts_id[] = {
    { "i2c-ts", 0 },
    { }
};
MODULE_DEVICE_TABLE(i2c, i2c_ts_id);

static struct i2c_driver i2c_ts_driver = {
    .driver = {
        .name = "i2c-ts",
    },
    .probe = i2c_ts_probe,
    .remove = i2c_ts_remove,
    .suspend = i2c_ts_suspend,
    .resume = i2c_ts_resume,
    .id_table = i2c_ts_id,
};

static int __init i2c_ts_init(void)
{
    return i2c_add_driver(&i2c_ts_driver);
}

static void __exit i2c_ts_exit(void)
{
    i2c_del_driver(&i2c_ts_driver);
}

MODULE_DESCRIPTION("i2c Touchscreen driver");
MODULE_AUTHOR("ALlen <allen.p.wang@gmail.com>");
MODULE_LICENSE("GPL");

module_init(i2c_ts_init);
module_exit(i2c_ts_exit);

4).实现如上步骤后，还需要创建和配置I2C 设备,设置文件位于
linux-2.6.32.2/arch/arm/mach-s3c2440/mach-mini2440.c中，
添加如下代码：
..................................................
+/* I2C touch screen devices. */
+/* bus configuration */
+static struct s3c2410_platform_i2c i2c_touchscreen_cfg __initdata = {
+   .flags        = 0,
+    .slave_addr    = 0x5c,
+   .frequency    = 100*1000,
+    .sda_delay    = 2,
+};

+/* i2c device name is "i2c_ts", address is 0x5c, interrupt is eint20 */
+static struct i2c_board_info touchscreen_i2c_devs[] __initdata = {
+    {
+        I2C_BOARD_INFO("i2c-ts", 0x5c),
+        .irq    = IRQ_EINT20,
+    },
+};
...................................................

static void __init mini2440_machine_init(void)
{
..................................................
 +   /* i2c touch screen devices */
 +   s3c_i2c0_set_platdata(&i2c_touchscreen_cfg);
 +  i2c_register_board_info(0, touchscreen_i2c_devs,  +ARRAY_SIZE(touchscreen_i2c_devs));
...................................................
}

此处I2C_BOARD_INFO("i2c-ts",0x5c), “i2c-ts” 要和i2c设备驱动中i2c_ts_id一致。
才能保证i2c设备驱动成功加载。