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 mutex		ecompass_lock;
	struct mutex		ops_lock;
	struct workqueue_struct *data_wq;
	struct delayed_work	dwork;
	struct sensors_classdev	cdev;
	struct mmc3524x_vec	last;

	struct i2c_client	*i2c;
	struct input_dev	*idev;
	struct regulator	*vdd;
	struct regulator	*vio;
	struct regmap		*regmap;

	int			dir;
	int			auto_report;
	int			enable;
	int			poll_interval;
	int			power_enabled;
	unsigned long		timeout;

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: %sn",
			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=%ldn", data);
		return -EINVAL;
	}

	if (sensors_cdev->sensors_enable == NULL) {
		dev_err(dev, "Invalid sensor class enable handlen");
		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, "%un",
			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 failedn");
			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 failedn");
	} else {
		dev_warn(&memsic->i2c->dev,
				"ignore enable state change from %d to %dn",
				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 failedn");
		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));
}

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