input|input 子系统的分析与学习（二） input子系统的分析与学习（二）

下面分析一下自己实现的光传感器的驱动。先附上代码：

#include #include #include #include #include #include #include #include #include #define EVENT_TYPE_LIGHTABS_MISC #define LIGHTSENSOR_NAME"lightsensor" #define S5PV210_SENSOR_CHANNEL2 #define INIT_POLL_INTERVAL10000#define sensor_dbg(format, arg...) do {\ printk("%s : " format , __func__,## arg) ; \ } while (0)static DEFINE_MUTEX(sensor_mutex); MODULE_LICENSE("GPL"); MODULE_DESCRIPTION("Light Sensor Driver"); struct lightsensor_data { struct input_polled_dev *input_poll_dev; atomic_t enabled; intlight_value; }; static struct lightsensor_data *sensor_data; static int poll_cnt = 0; static int lightsensor_set_value(struct lightsensor_data *sensor, int value) { mutex_lock(&sensor_mutex); sensor->light_value =https://www.it610.com/article/value; mutex_unlock(&sensor_mutex); return 0; }static int lightsensor_get_value(struct lightsensor_data *sensor) { printk("%s%d\n", __func__,sensor->light_value); int ret; mutex_lock(&sensor_mutex); ret= sensor->light_value ; mutex_unlock(&sensor_mutex); return ret; }void lightsensor_input_poll_func(struct input_polled_dev *input) { struct lightsensor_data *sensor = input->private; u32 enabled = atomic_read(&sensor->enabled); printk("%s, sensor %p enabled: %u,light_value:%d poll_rate: %d \n", __func__, sensor, enabled, sensor->light_value,sensor->input_poll_dev->poll_interval); if(enalbed) { // int value = https://www.it610.com/article/mini2440_adc_get_light(); int value = poll_cnt++; input_event(input->input, EV_FF, EVENT_TYPE_LIGHT,value); input_sync(input->input); sensor_dbg("input_report\n"); // lightsensor_set_value( sensor, value); }//else // sensor_dbg("input_not report\n"); }static intlightsensor_enable(struct lightsensor_data *sensor) { // open the input dev struct input_dev*input = sensor->input_poll_dev->input; atomic_cmpxchg(&sensor->enabled, 0, 1); return 0; }static intlightsensor_disable(struct lightsensor_data *sensor) { // close the input dev struct input_dev*input = sensor->input_poll_dev->input; atomic_cmpxchg(&sensor->enabled, 1, 0) ; return 0; }static ssize_t attr_polling_rate_show(struct device *dev, struct device_attribute *attr, char *buf) { unsigned int val; struct lightsensor_data *sensor = sensor_data; mutex_lock(&sensor_mutex); val = sensor->input_poll_dev->poll_interval; mutex_unlock(&sensor_mutex); return sprintf(buf, "%u\n", val); }static ssize_t attr_polling_rate_store(struct device *dev, struct device_attribute *attr, const char *buf, size_t size) { struct lightsensor_data *sensor = sensor_data; long interval_ms; if (strict_strtol(buf, 10, &interval_ms)) return -EINVAL; if (!interval_ms) return -EINVAL; mutex_lock(&sensor_mutex); sensor->input_poll_dev->poll_interval = interval_ms; mutex_unlock(&sensor_mutex); return size; }static ssize_t attr_enable_show(struct device *dev, struct device_attribute *attr, char *buf) { struct lightsensor_data *sensor = sensor_data; u32 val = atomic_read(&sensor->enabled); return sprintf(buf, "%d\n", val); }static ssize_t attr_enable_store(struct device *dev, struct device_attribute *attr, const char *buf, size_t size) { struct lightsensor_data *sensor = sensor_data; unsigned long val; if (strict_strtoul(buf, 10, &val)) return -EINVAL; if (val) lightsensor_enable(sensor); else lightsensor_disable(sensor); return size; }static ssize_tattr_light_value_show(struct device *dev, struct device_attribute *attr, char *buf) { //input_get_drvdata is obidient here, because input_get_drvdata = https://www.it610.com/article/sensor_data->input_poll_dev struct lightsensor_data *sensor = sensor_data; int val = lightsensor_get_value(sensor); printk("%s: sensor_data %p, sensor %p val %d\n", __func__, sensor_data, sensor, val); return sprintf(buf, "%d\n", val); }static struct device_attribute attributes[] = { __ATTR(pollrate_ms, 0666, attr_polling_rate_show, attr_polling_rate_store), __ATTR(enable_device, 0666, attr_enable_show, attr_enable_store), __ATTR(light_value, 0444, attr_light_value_show, NULL), }; static int create_sysfs_interfaces(struct device *dev) { int i; for (i = 0; i < ARRAY_SIZE(attributes); i++) if (device_create_file(dev, attributes + i)) goto error; return 0; error: printk("%s error, i = %d\n", __func__, i ); for ( ; i >= 0; i--) device_remove_file(dev, attributes + i); dev_err(dev, "%s:Unable to create interface\n", __func__); return -1; }static int remove_sysfs_interfaces(struct device *dev) { int i; for (i = 0; i < ARRAY_SIZE(attributes); i++) device_remove_file(dev, attributes + i); return 0; }static int __init lightsensor_init(void) { int ret = -1; struct input_dev *input; sensor_data= https://www.it610.com/article/kmalloc(sizeof(struct lightsensor_data),GFP_KERNEL) ; if(!sensor_data) { printk("kmalloc\n"); goto kmalloc_error; } sensor_data->input_poll_dev = input_allocate_polled_device(); if(! sensor_data->input_poll_dev) { sensor_dbg("error\n"); goto alloc_error; } sensor_data->input_poll_dev->private = sensor_data; sensor_data->input_poll_dev->poll = lightsensor_input_poll_func; sensor_data->input_poll_dev->poll_interval = INIT_POLL_INTERVAL; input = sensor_data->input_poll_dev->input; input->name = LIGHTSENSOR_NAME; //input_set_drvdata(sensor_data->input_poll_dev->input, sensor_data); set_bit(EV_FF, input->evbit); ret = input_register_polled_device(sensor_data->input_poll_dev); if(ret) { printk("input_register_polled_device error\n"); return ret; } sensor_dbg("\n"); atomic_set(&sensor_data->enabled, 0); sensor_data->light_value = https://www.it610.com/article/88; printk("%ssensor->light_value:%d \n ",__func__,sensor_data->light_value); if ( create_sysfs_interfaces(&input->dev) ) { printk("create_sysfs_interface failed\n"); goto sys_error; } return ret; sys_error: input_unregister_polled_device(sensor_data->input_poll_dev); alloc_error: kfree(sensor_data); kmalloc_error: return ret; }static void __exit lightsensor_exit(void) { remove_sysfs_interfaces( &sensor_data->input_poll_dev->input->dev); input_unregister_polled_device(sensor_data->input_poll_dev); input_free_polled_device(sensor_data->input_poll_dev); kfree(sensor_data); }module_init(lightsensor_init); module_exit(lightsensor_exit);

我将这个设备实现成了一个input_poll_dev，这个设备的具体实现是在driver/input/input-polldev.c中的。我们这里是用了一个它的模型。因为我们的光传感器要做的事情就是周期性的向应用程序汇报光的值。而input-polldev正好实现了这个功能，具体到我们的光传感器主要就是要实现Poll这个函数。为了实现控制这个光传感器，另外增加了sysfs中的接口enable、 pollrate 、light_value。可以看到利用Inut子系统，我们在写驱动时候就非常的方便。

对应的在用户态的应用程序如下：

#include #include #include #include #include #include #include #define INPUTFILE "/dev/input/event0" int gotdata=https://www.it610.com/article/0; void sighandler(int signo) { if (signo==SIGIO) gotdata++; return; }char buffer[4096]; int main(int argc, char **argv) { int count; struct sigaction action; struct input_event event; int fd = open(INPUTFILE, O_RDONLY); memset(&action, 0, sizeof(action)); action.sa_handler = sighandler; action.sa_flags = 0; sigaction(SIGIO, &action, NULL); fcntl(fd, F_SETOWN, getpid()); fcntl(fd, F_SETFL, fcntl(STDIN_FILENO, F_GETFL) | FASYNC); while(1) { /* this only returns if a signal arrives */ sleep(86400); /* one day */ if (!gotdata) continue; count=read(fd, &event, sizeof(event)); printf("event: %d %d %d\n", event.type, event.code, event.value); /* buggy: if avail data is more than 4kbytes... */ gotdata=https://www.it610.com/article/0; } }

刚开始看这个input子系统时，知道驱动report了event，但是不知道该去哪里读，自己研究半天。终于找到了对应的可操作的文件就是 /dev/input/inputX这些文件。其中/dev/input/是在/dev系统里面创建了一个目录，应该也是利用device_create接口创建的，但是目前自己还不是很明确在/dev下面创建directory的方法。明天再继续看。

这样利用input子系统，一个光传感器的驱动就写好了。代码量很少。
另外，在input子系统中，事件的汇报采用的是异步的机制，也就是说当report event时，也会向应用程序发送SIGIO信号，因此只要在应用程序中将file设置成异步模式，就可以读到SIGNO信号，然后在中断程序中读取信号，也是可以的。因为event都是不可预知的，所以采用异步的方式更加科学。
【input|input 子系统的分析与学习（二）】
记录一下，我在写这个驱动时候，犯的错误，自己调试了很长时间。
1. 首先，我在写lightsensor.c时，给input_dev注册了自己的read\write 函数。就像注册poll函数一样。
sensor_data->input_poll_dev->read = lightsensor_input_read_func; 但是这些函数总是不被调用。后来发现是，在调用input_register_polled_device(sensor_data->input_poll_dev)时，这里会注册新的open\read\write函数，在open的时候创建delayd work queue。所以我们在用input_poll_dev时，自己只需要实现poll函数就好了，如果注册了其他函数，并替换掉了inpu_poll_dev本身的函数，就会导致这个设备不能正常的工作。
2.关于sysfs 的错误，这个错误自己也调试了挺长时间。其实就是由于input_get_drvdata和input_set_drvdata的使用有误造成的。我在lightsensor.c 中，设置了dev的private，input_set_drvdata(sensor_data->input_poll_dev->input, sensor_data); 然后在 sysfs的static ssize_t attr_polling_rate_store(struct device *dev, struct device_attribute *attr, const char *buf, size_t size) 函数中调用input_get_drvdata，但是得到的指针指向的不是sensor_data。我以为是sysfs的使用错误，调试了很久。结果发现是在input_poll_dev中也使用了这个函数对，将这个指针指向了别的地方。所以，这就更说明了一点，在我们基于input_poll_dev实现的设备中，不能利用input_poll_dev中使用的input_dev的方法。编程时需要非常的注意，否则就会因为小错调试很长时间。

明天继续分析INPUT子系统中几个重要的结构体。