Sensor在Linux内核中的驱动分析

内核中对sensor的抽象：drivers/sensors/sensors_class.c
模块初始化函数：

static int __init sensors_init(void){sensors_class = class_create(THIS_MODULE, "sensors");if (IS_ERR(sensors_class))return PTR_ERR(sensors_class);sensors_class->dev_attrs = sensors_class_attrs;return 0;}

创建sensor的类class，通过sensors_class->dev_attrs = sensors_class_attrs;在sysfs文件系统下面创建设备节点，上层调用读写函数往文件节点读写数据时，相应的show和store函数就会被调用。sensors_class_attrs的定义如下：

static struct device_attribute sensors_class_attrs[] = {__ATTR(name, 0444, sensors_name_show, NULL),__ATTR(vendor, 0444, sensors_vendor_show, NULL),__ATTR(version, 0444, sensors_version_show, NULL),__ATTR(handle, 0444, sensors_handle_show, NULL),__ATTR(type, 0444, sensors_type_show, NULL),__ATTR(max_range, 0444, sensors_max_range_show, NULL),__ATTR(resolution, 0444, sensors_resolution_show, NULL),__ATTR(sensor_power, 0444, sensors_power_show, NULL),__ATTR(min_delay, 0444, sensors_min_delay_show, NULL),__ATTR(fifo_reserved_event_count, 0444, sensors_fifo_event_show, NULL),__ATTR(fifo_max_event_count, 0444, sensors_fifo_max_show, NULL),__ATTR(max_delay, 0444, sensors_max_delay_show, NULL),__ATTR(flags, 0444, sensors_flags_show, NULL),__ATTR(enable, 0664, sensors_enable_show, sensors_enable_store),__ATTR(enable_wakeup, 0664, sensors_enable_wakeup_show,sensors_enable_wakeup_store),__ATTR(poll_delay, 0664, sensors_delay_show, sensors_delay_store),__ATTR(self_test, 0440, sensors_test_show, NULL),__ATTR(max_latency, 0660, sensors_max_latency_show,sensors_max_latency_store),__ATTR(flush, 0660, sensors_flush_show, sensors_flush_store),__ATTR(calibrate, 0664, sensors_calibrate_show,sensors_calibrate_store),__ATTR_NULL,};

具体的sensor驱动程序会调用sensors_classdev_register函数注册自己，以地磁传感器mmc3524为例，在驱动的proble函数中，有如下代码：

memsic->cdev = sensors_cdev;memsic->cdev.sensors_enable = mmc3524x_set_enable;memsic->cdev.sensors_poll_delay = mmc3524x_set_poll_delay;res = sensors_classdev_register(&memsic->idev->dev, &memsic->cdev);

mmc3524的数据结构如下，里面有个struct sensors_classdev    cdev;成员，上面的代码设置cdev的enable和poll_delay函数指针指向驱动程序的函数，供sensor的HAL层调用。

struct mmc3524x_data {struct mutexecompass_lock;struct mutexops_lock;struct workqueue_struct *data_wq;struct delayed_workdwork;struct sensors_classdevcdev;struct mmc3524x_veclast;struct i2c_client*i2c;struct input_dev*idev;struct regulator*vdd;struct regulator*vio;struct regmap*regmap;intdir;intauto_report;intenable;intpoll_interval;intpower_enabled;unsigned longtimeout;

sensors_classdev_register函数是sensor的核心，该函数根据之前创建的sensors_class，在类下面创建设备，前面调用sensors_classdev_register(&memsic->idev->dev, &memsic->cdev);时，将memsic->cdev成员的地址作为device_create函数的第四个参数传入，然后将sensors_cdev放入sensors_list链表。

int sensors_classdev_register(struct device *parent,struct sensors_classdev *sensors_cdev){sensors_cdev->dev = device_create(sensors_class, parent, 0,      sensors_cdev, "%s", sensors_cdev->name);if (IS_ERR(sensors_cdev->dev))return PTR_ERR(sensors_cdev->dev);down_write(&sensors_list_lock);list_add_tail(&sensors_cdev->node, &sensors_list);up_write(&sensors_list_lock);pr_debug("Registered sensors device: %s\n",sensors_cdev->name);return 0;}

在device_create函数中，调用device_create_vargs将之前传入的&memsic->cdev传入device_create_vargs函数中。

struct device *device_create(struct class *class, struct device *parent,     dev_t devt, void *drvdata, const char *fmt, ...){va_list vargs;struct device *dev;va_start(vargs, fmt);dev = device_create_vargs(class, parent, devt, drvdata, fmt, vargs);va_end(vargs);return dev;}

在device_create_vargs函数中，会调用dev_set_drvdata(dev, drvdata);

struct device *device_create_vargs(struct class *class, struct device *parent,   dev_t devt, void *drvdata, const char *fmt,   va_list args){struct device *dev = NULL;int retval = -ENODEV;if (class == NULL || IS_ERR(class))goto error;dev = kzalloc(sizeof(*dev), GFP_KERNEL);if (!dev) {retval = -ENOMEM;goto error;}dev->devt = devt;dev->class = class;dev->parent = parent;dev->release = device_create_release;dev_set_drvdata(dev, drvdata);retval = kobject_set_name_vargs(&dev->kobj, fmt, args);if (retval)goto error;retval = device_register(dev);if (retval)goto error;return dev;error:put_device(dev);return ERR_PTR(retval);}dev_set_drvdata

在dev_set_drvdata函数中，会调用dev->p->driver_data = data;这样dev->p->driver_data就指向了&memsic->cdev。

int dev_set_drvdata(struct device *dev, void *data){int error;if (!dev->p) {error = device_private_init(dev);if (error)return error;}dev->p->driver_data = data;return 0;}

在sensors_enable_store和sensors_enable_show函数中，会调用dev_get_drvdata函数：

static ssize_t sensors_enable_store(struct device *dev,struct device_attribute *attr, const char *buf, size_t size){struct sensors_classdev *sensors_cdev = dev_get_drvdata(dev);ssize_t ret = -EINVAL;unsigned long data = 0;ret = kstrtoul(buf, 10, &data);if (ret)return ret;if (data > 1) {dev_err(dev, "Invalid value of input, input=%ld\n", data);return -EINVAL;}if (sensors_cdev->sensors_enable == NULL) {dev_err(dev, "Invalid sensor class enable handle\n");return -EINVAL;}ret = sensors_cdev->sensors_enable(sensors_cdev, data);if (ret)return ret;sensors_cdev->enabled = data;return size;}static ssize_t sensors_enable_show(struct device *dev,struct device_attribute *attr, char *buf){struct sensors_classdev *sensors_cdev = dev_get_drvdata(dev);return snprintf(buf, PAGE_SIZE, "%u\n",sensors_cdev->enabled);}

dev_get_drvdata函数会返回之前在dev_set_drvdata函数中设置的指针dev->p->driver_data。

void *dev_get_drvdata(const struct device *dev){if (dev && dev->p)return dev->p->driver_data;return NULL;}

之前在驱动的probe函数中设置了memsic->cdev.sensors_enable = mmc3524x_set_enable;sensors_enable_store函数通过ret = sensors_cdev->sensors_enable(sensors_cdev, data);来调用驱动程序中的enable函数。HAL层会根据sensor的设备节点来找到sensor，调用enable，delay等函数来调用sensor驱动中对应的函数，本例子中对应的文件是：hardware/qcom/sensors/CompassSensor.cpp：

int CompassSensor::enable(int32_t, int en) {int flags = en ? 1 : 0;compass_algo_args arg;arg.common.enable = flags;char propBuf[PROPERTY_VALUE_MAX];property_get("sensors.compass.loopback", propBuf, "0");if (strcmp(propBuf, "1") == 0) {ALOGE("sensors.compass.loopback is set");mEnabled = flags;mEnabledTime = 0;return 0;}if (flags != mEnabled) {int fd;if ((algo != NULL) && (algo->methods->config != NULL)) {if (algo->methods->config(CMD_ENABLE, (sensor_algo_args*)&arg)) {ALOGW("Calling enable config failed for compass");}}strlcpy(&input_sysfs_path[input_sysfs_path_len],SYSFS_ENABLE, SYSFS_MAXLEN);fd = open(input_sysfs_path, O_RDWR);if (fd >= 0) {char buf[2];int err;buf[1] = 0;if (flags) {buf[0] = '1';mEnabledTime = getTimestamp() + IGNORE_EVENT_TIME;} else {buf[0] = '0';}err = write(fd, buf, sizeof(buf));close(fd);mEnabled = flags;return 0;}ALOGE("CompassSensor: failed to open %s", input_sysfs_path);return -1;}return 0;}

HAL层的enable函数中，通过write系统调用来调用内核的enable函数，内核的enable函数首先会打开设备的电源，然后通过工作队列函数queue_delayed_work(memsic->data_wq,&memsic->dwork,msecs_to_jiffies(memsic->poll_interval));来调用sensor的mmc3524x_poll函数。

static int mmc3524x_set_enable(struct sensors_classdev *sensors_cdev,unsigned int enable){int rc = 0;struct mmc3524x_data *memsic = container_of(sensors_cdev,struct mmc3524x_data, cdev);mutex_lock(&memsic->ops_lock);if (enable && (!memsic->enable)) {rc = mmc3524x_power_set(memsic, true);if (rc) {dev_err(&memsic->i2c->dev, "Power up failed\n");goto exit;}/* send TM cmd before read */rc = regmap_write(memsic->regmap, MMC3524X_REG_CTRL,MMC3524X_CTRL_TM);if (rc) {dev_err(&memsic->i2c->dev, "write reg %d failed.(%d)\n",MMC3524X_REG_CTRL, rc);goto exit;}memsic->timeout = jiffies;if (memsic->auto_report)queue_delayed_work(memsic->data_wq,&memsic->dwork,msecs_to_jiffies(memsic->poll_interval));} else if ((!enable) && memsic->enable) {if (memsic->auto_report)cancel_delayed_work_sync(&memsic->dwork);if (mmc3524x_power_set(memsic, false))dev_warn(&memsic->i2c->dev, "Power off failed\n");} else {dev_warn(&memsic->i2c->dev,"ignore enable state change from %d to %d\n",memsic->enable, enable);}memsic->enable = enable;exit:mutex_unlock(&memsic->ops_lock);return rc;

mmc3524x_poll函数通过I2C接口获取数据，上报数据。

static void mmc3524x_poll(struct work_struct *work){int ret;s8 *tmp;struct mmc3524x_vec vec;struct mmc3524x_vec report;struct mmc3524x_data *memsic = container_of((struct delayed_work *)work,struct mmc3524x_data, dwork);ktime_t timestamp;vec.x = vec.y = vec.z = 0;ret = mmc3524x_read_xyz(memsic, &vec);if (ret) {dev_warn(&memsic->i2c->dev, "read xyz failed\n");goto exit;}tmp = &mmc3524x_rotation_matrix[memsic->dir][0];report.x = tmp[0] * vec.x + tmp[1] * vec.y + tmp[2] * vec.z;report.y = tmp[3] * vec.x + tmp[4] * vec.y + tmp[5] * vec.z;report.z = tmp[6] * vec.x + tmp[7] * vec.y + tmp[8] * vec.z;timestamp = ktime_get_boottime();input_report_abs(memsic->idev, ABS_X, report.x);input_report_abs(memsic->idev, ABS_Y, report.y);input_report_abs(memsic->idev, ABS_Z, report.z);input_event(memsic->idev,EV_SYN, SYN_TIME_SEC,ktime_to_timespec(timestamp).tv_sec);input_event(memsic->idev,EV_SYN, SYN_TIME_NSEC,ktime_to_timespec(timestamp).tv_nsec);input_sync(memsic->idev);exit:queue_delayed_work(memsic->data_wq,&memsic->dwork,msecs_to_jiffies(memsic->poll_interval));}