S3C2440驱动简析——触摸屏驱动

S3C2440驱动简析——触摸屏驱动

    本文将简要分析2440的触摸屏驱动，其驱动程序内核自带。在浏览本文之前，如果对Linux 驱动的input 子系统没有认识的话，请先回头参考鄙人之前的博文《input子系统》http://blog.csdn.net/jarvis_xian/article/details/6552579

 

    事不宜迟，马上进入本文的正题。有经验的朋友都知道，看驱动，先找入口、出口！

<span style="font-size:18px;">static int __init s3c2410ts_init(void)
{
    return platform_driver_register(&s3c_ts_driver);//注册platform驱动，注意参数s3c_ts_driver
}

static void __exit s3c2410ts_exit(void)
{
    platform_driver_unregister(&s3c_ts_driver);   //注销platform驱动
}</span>

platform_driver_register 的参数s3c_ts_driver 定义如下

<span style="font-size:18px;">static struct platform_driver s3c_ts_driver = {
    .driver         = {
        .name   = "samsung-ts",
        .owner  = THIS_MODULE,
#ifdef CONFIG_PM
        .pm = &s3c_ts_pmops,
#endif
    },
    .id_table   = s3cts_driver_ids,
    .probe      = s3c2410ts_probe,
    .remove     = __devexit_p(s3c2410ts_remove),
};</span>

在上述结构体中，我们应该把精力放在.probe、.remove和.pm上

探讨probe 函数前，我们先看一下结构体ts 的定义，其统筹了整个驱动所用到的资源

<span style="font-size:18px;">struct s3c2410ts {
    struct s3c_adc_client *client;
    struct device *dev;
    struct input_dev *input;
    struct clk *clock;
    void __iomem *io;
    unsigned long xp;
    unsigned long yp;
    int irq_tc;
    int count;
    int shift;
    int features;
};</span>

s3c2410ts_probe代码如下：

<span style="font-size:18px;">static int __devinit s3c2410ts_probe(struct platform_device *pdev)
{
    struct s3c2410_ts_mach_info *info;
    struct device *dev = &pdev->dev;
    struct input_dev *input_dev;
    struct resource *res;
    int ret = -EINVAL;

    /* Initialise input stuff */
    memset(&ts, 0, sizeof(struct s3c2410ts));

    ts.dev = dev;   //把platform的设备挂到ts 结构体

    info = pdev->dev.platform_data;
    if (!info) {
        dev_err(dev, "no platform data, cannot attach\n");
        return -EINVAL;
    }

    dev_dbg(dev, "initialising touchscreen\n");

    ts.clock = clk_get(dev, "adc");   //得到adc 时钟资源
    if (IS_ERR(ts.clock)) {
        dev_err(dev, "cannot get adc clock source\n");
        return -ENOENT;
    }

    clk_enable(ts.clock);   //使能ts 时钟
    dev_dbg(dev, "got and enabled clocks\n");

    ts.irq_tc = ret = platform_get_irq(pdev, 0);   //获取中断资源
    if (ret < 0) {
        dev_err(dev, "no resource for interrupt\n");
        goto err_clk;
    }

    res = platform_get_resource(pdev, IORESOURCE_MEM, 0);   //获取占用端口的大小
    if (!res) {
        dev_err(dev, "no resource for registers\n");
        ret = -ENOENT;
        goto err_clk;
    }

    ts.io = ioremap(res->start, resource_size(res));   //物理地址映射到虚拟地址
    if (ts.io == NULL) {
        dev_err(dev, "cannot map registers\n");
        ret = -ENOMEM;
        goto err_clk;
    }

    /* inititalise the gpio */
    if (info->cfg_gpio)
        info->cfg_gpio(to_platform_device(ts.dev));

    ts.client = s3c_adc_register(pdev, s3c24xx_ts_select,
                     s3c24xx_ts_conversion, 1);
    if (IS_ERR(ts.client)) {
        dev_err(dev, "failed to register adc client\n");
        ret = PTR_ERR(ts.client);
        goto err_iomap;
    }

    /* Initialise registers */
    if ((info->delay & 0xffff) > 0)
        writel(info->delay & 0xffff, ts.io + S3C2410_ADCDLY);   //初始化延时寄存器

    writel(WAIT4INT | INT_DOWN, ts.io + S3C2410_ADCTSC);

    input_dev = input_allocate_device();   //为input_dev 分配空间并初始化
    if (!input_dev) {
        dev_err(dev, "Unable to allocate the input device !!\n");
        ret = -ENOMEM;
        goto err_iomap;
    }

    ts.input = input_dev;   //把input_dev 挂接到ts 结构体
    ts.input->evbit[0] = BIT_MASK(EV_KEY) | BIT_MASK(EV_ABS); //设置事件类型
    ts.input->keybit[BIT_WORD(BTN_TOUCH)] = BIT_MASK(BTN_TOUCH);
    input_set_abs_params(ts.input, ABS_X, 0, 0x3FF, 0, 0);   //设置边界条件等
    input_set_abs_params(ts.input, ABS_Y, 0, 0x3FF, 0, 0);

    ts.input->name = "S3C24XX TouchScreen";
    ts.input->id.bustype = BUS_HOST;
    ts.input->id.vendor = 0xDEAD;
    ts.input->id.product = 0xBEEF;
    ts.input->id.version = 0x0102;

    ts.shift = info->oversampling_shift;
    ts.features = platform_get_device_id(pdev)->driver_data;

    ret = request_irq(ts.irq_tc, stylus_irq, IRQF_DISABLED,
              "s3c2410_ts_pen", ts.input);
    if (ret) {
        dev_err(dev, "cannot get TC interrupt\n");
        goto err_inputdev;
    }

    dev_info(dev, "driver attached, registering input device\n");

    /* All went ok, so register to the input system */
    ret = input_register_device(ts.input);   //初始化完毕后，注册input 子系统
    if (ret < 0) {
        dev_err(dev, "failed to register input device\n");
        ret = -EIO;
        goto err_tcirq;
    }

    return 0;

 err_tcirq:
    free_irq(ts.irq_tc, ts.input);
 err_inputdev:
    input_free_device(ts.input);
 err_iomap:
    iounmap(ts.io);
 err_clk:
    del_timer_sync(&touch_timer);
    clk_put(ts.clock);
    return ret;
}</span>

<span style="font-size:18px;"> </span>

<span style="font-size:18px;">相对于probe，remove的代码如下</span><pre class="cpp" name="code"><span style="font-size:18px;">static int __devexit s3c2410ts_remove(struct platform_device *pdev)
{
    free_irq(ts.irq_tc, ts.input);   //释放中断资源
    del_timer_sync(&touch_timer);   //卸载软件时钟

    clk_disable(ts.clock);   //禁能
    clk_put(ts.clock);

    input_unregister_device(ts.input);   //注销输入子系统
    iounmap(ts.io);   //解除地址映射

    return 0;
}</span>

<span style="font-size:18px;"> </span>

<span style="font-size:18px;">至于上文提及的.pm，实则也是一个结构体，如下</span><pre class="cpp" name="code"><span style="font-size:18px;">static struct dev_pm_ops s3c_ts_pmops = {
    .suspend    = s3c2410ts_suspend,
    .resume     = s3c2410ts_resume,
};
包含了suspend 和resume 两个操作。</span>

<span style="font-size:18px;"> </span>

<span style="font-size:18px;">s3c2410ts_suspend函数代码：</span><pre class="cpp" name="code"><span style="font-size:18px;">static int s3c2410ts_suspend(struct device *dev)
{
    writel(TSC_SLEEP, ts.io + S3C2410_ADCTSC);   //把挂起状态写入硬件寄存器
    disable_irq(ts.irq_tc);
    clk_disable(ts.clock);

    return 0;
}</span>

<span style="font-size:18px;"> </span>

<span style="font-size:18px;">s3c2410ts_resume函数代码：</span><pre class="cpp" name="code"><span style="font-size:18px;">static int s3c2410ts_resume(struct device *dev)
{
    struct platform_device *pdev = to_platform_device(dev);
    struct s3c2410_ts_mach_info *info = pdev->dev.platform_data;

    clk_enable(ts.clock);
    enable_irq(ts.irq_tc);

    /* Initialise registers */
    if ((info->delay & 0xffff) > 0)   //写入延时初值
        writel(info->delay & 0xffff, ts.io + S3C2410_ADCDLY);

    writel(WAIT4INT | INT_DOWN, ts.io + S3C2410_ADCTSC);   //写入工作状态

    return 0;
}</span>

<span style="font-size:18px;"> </span>

<span style="font-size:18px;">经过上述代码的铺垫，我们已经有了一个舒适的环境，剩下的工作，就在与中断相关的函数里完成了。</span>

<pre class="cpp" name="code"><span style="font-size:18px;">static irqreturn_t stylus_irq(int irq, void *dev_id)
{
    unsigned long data0;
    unsigned long data1;
    bool down;

    data0 = readl(ts.io + S3C2410_ADCDAT0);   //读取X、Y轴坐标
    data1 = readl(ts.io + S3C2410_ADCDAT1);

    down = get_down(data0, data1);   //关于get_down函数查看下文

    /* TODO we should never get an interrupt with down set while
     * the timer is running, but maybe we ought to verify that the
     * timer isn't running anyways. */

    if (down)
        s3c_adc_start(ts.client, 0, 1 << ts.shift);   //开始ADC转换
    else
        dev_dbg(ts.dev, "%s: count=%d\n", __func__, ts.count);

    if (ts.features & FEAT_PEN_IRQ) {   //清除标志位（等待下一次中断的到来）
        /* Clear pen down/up interrupt */
        writel(0x0, ts.io + S3C64XX_ADCCLRINTPNDNUP);
    }

    return IRQ_HANDLED;
}</span><pre class="cpp" name="code"><span style="font-size:18px;">static inline bool get_down(unsigned long data0, unsigned long data1)
{   //检测触摸屏有没有被按下
    /* returns true if both data values show stylus down */
    return (!(data0 & S3C2410_ADCDAT0_UPDOWN) &&
        !(data1 & S3C2410_ADCDAT0_UPDOWN));
}</span>

<span style="font-size:18px;"> </span>

<span style="font-size:18px;">touch_timer_fire函数将触摸屏的数据报告给内核</span>

<pre class="cpp" name="code"><span style="font-size:18px;">static void touch_timer_fire(unsigned long data)
{
    unsigned long data0;
    unsigned long data1;
    bool down;

    data0 = readl(ts.io + S3C2410_ADCDAT0);
    data1 = readl(ts.io + S3C2410_ADCDAT1);

    down = get_down(data0, data1);

    if (down) {
        if (ts.count == (1 << ts.shift)) {
            ts.xp >>= ts.shift;
            ts.yp >>= ts.shift;

            dev_dbg(ts.dev, "%s: X=%lu, Y=%lu, count=%d\n",
                __func__, ts.xp, ts.yp, ts.count);

            input_report_abs(ts.input, ABS_X, ts.xp);   //熟悉的操作~~~
            input_report_abs(ts.input, ABS_Y, ts.yp);

            input_report_key(ts.input, BTN_TOUCH, 1);
            input_sync(ts.input);   //结束同步

            ts.xp = 0;
            ts.yp = 0;
            ts.count = 0;
        }

        s3c_adc_start(ts.client, 0, 1 << ts.shift);
    } else {
        ts.xp = 0;
        ts.yp = 0;
        ts.count = 0;

        input_report_key(ts.input, BTN_TOUCH, 0);
        input_sync(ts.input);

        writel(WAIT4INT | INT_DOWN, ts.io + S3C2410_ADCTSC);
    }
}</span>

 最后，我们可以看到触摸屏驱动是基于platform + input子系统 搭建起来的，正如搭积木一样，只要理解了每一个系统、部件的特点和接口等等，再稍加努力消化，就可把各式简单驱动程序的架构辨清，继而为自己编写驱动或者修改驱动打下了一个良好的基础。以上仅是菜鸟之愚见，还请前辈多多指教！