将DHT11移植到Linux系统上续

       从网上，看到一篇关于dht11驱动的文章，该驱动是通过中断的方式实现的。中断能及时读取dht11的数据，是否就能保证读取到的数据都是正确的呢。将驱动稍作修改后,读出来的数据出错的概率很小。每次进入中断的次数一定，有可能do_gettimeofday(&dev->tv)获取到的时间有可能受到内核调度的影响（优先级高的中断可打断其他优先级低的中断）。原文链接 http://blog.youkuaiyun.com/jvaemape/article/details/36004393

#include <linux/module.h>
#include <linux/workqueue.h>
#include <linux/slab.h>
#include <linux/input.h>
#include <linux/init.h>
#include <linux/errno.h>
#include <linux/serio.h>
#include <linux/delay.h>
#include <linux/clk.h>
#include <linux/wait.h>
#include <linux/sched.h>
#include <linux/cdev.h>
#include <linux/miscdevice.h>
#include <linux/fs.h>
#include <linux/gpio.h>
#include <linux/delay.h>
#include <linux/printk.h>
#include <linux/time.h>
#include <linux/irq.h>
#include <asm-generic/uaccess.h>

#define DEVICE_NAME "dht11"
#define DHT11_PIN S5PV210_GPH0(0)
#define DEVICE_MAJOR 0

struct dht11_sensor_dev{
	unsigned long pin;
	unsigned char value[5];
	unsigned int irq;	
	int bitcount;
	int bytecount;
	int started;
	int signal;
	int time;
	int count;
	dev_t devno;
	struct class *dht11_class;
	struct cdev cdev;
	struct mutex read_data;
	struct timeval lasttv;
	struct timeval tv;
	struct work_struct dht11_work;
};

static struct dht11_sensor_dev *dht11_dev;

static void dht11_data_factory(struct work_struct *work)
{
		long deltv = 0;
		mutex_lock(&dht11_dev->read_data);
		dht11_dev->count++;
		deltv = dht11_dev->tv.tv_sec - dht11_dev->lasttv.tv_sec;
		dht11_dev->time = (int)(deltv * 1000000 + (dht11_dev->tv.tv_usec - dht11_dev->lasttv.tv_usec)); 
		dht11_dev->lasttv = dht11_dev->tv;
		if((dht11_dev->signal == 1) && (dht11_dev->time>40))
		{
			dht11_dev->started = 1;		
		}
		else
		{
		   if((dht11_dev->signal == 0) && (dht11_dev->started == 1))
		  {		
				dht11_dev->started = 0;
				if((dht11_dev->time>20)&&dht11_dev->time <38)
				{
					dht11_dev->bitcount++;
					if(dht11_dev->bitcount == 8)
					{
						dht11_dev->bitcount = 0;
						dht11_dev->bytecount++;
					}
				}
				if ((dht11_dev->time>55)&& (dht11_dev->time<80))
				{
					dht11_dev->value[dht11_dev->bytecount] = dht11_dev->value[dht11_dev->bytecount] | (0x80 >> dht11_dev->bitcount);			
					dht11_dev->bitcount++;
					if(dht11_dev->bitcount == 8)
					{
					dht11_dev->bitcount = 0;
					dht11_dev->bytecount++;
					}
				}
		 	}
		
		}
		mutex_unlock(&dht11_dev->read_data);
}

static irqreturn_t dht11_interrupt_hander(int irq, void *dev_id)
{
	struct dht11_sensor_dev *dev = (struct dht11_sensor_dev *)dev_id;
	dev->signal = gpio_get_value(dev->pin); 
	do_gettimeofday(&dev->tv);	
	schedule_work(&dht11_dev->dht11_work);
	return IRQ_HANDLED;
}

static int dht11_start(void)
{
    if(gpio_request(dht11_dev->pin, DEVICE_NAME))
	{  
        printk(KERN_INFO "[%s] gpio_request \n", __func__);  
        return -1;  
    }
	gpio_direction_output(dht11_dev->pin, 0);	
	msleep(30);
	gpio_set_value(dht11_dev->pin,1);
	udelay(30);
	gpio_direction_input(dht11_dev->pin);
	gpio_free(dht11_dev->pin);
	do_gettimeofday(&dht11_dev->lasttv);
	dht11_dev->count=0;
	return 0;
}


static int dht11_setup_interrupts(void)  
{  
    int result;    
    dht11_dev->irq = gpio_to_irq(dht11_dev->pin);  
    result = request_irq(dht11_dev->irq, dht11_interrupt_hander,   
            IRQ_TYPE_EDGE_BOTH, DEVICE_NAME, (void *)dht11_dev);  
  
    switch (result) 
	{  
        case -EBUSY:  
            printk(KERN_ERR "*%s(): IRQ %d is busy\n", __func__, dht11_dev->irq);  
            return -EBUSY;  
        case -EINVAL:  
            printk(KERN_ERR "*%s(): Bad irq number or handler\n", __func__);  
            return -EINVAL;  
        default:  
		//	printk("request irq for dht11 ok\n");
            return result;   
    }  
    
}  


static int dht11_clear_interrupts(void)  
{  
   free_irq(dht11_dev->irq, (void *)dht11_dev);
   msleep(20);
   if(gpio_request(dht11_dev->pin, DEVICE_NAME)){  
        printk(KERN_INFO "[%s] gpio_request \n", __func__);  
        return -1;  
    }
   gpio_direction_output(dht11_dev->pin, 1);
   gpio_free(dht11_dev->pin);
   return 1;
}  

static int dht11_checksum(struct dht11_sensor_dev *dev)
{
	int tmp = 0;
	tmp = dev->value[0] + dev->value[1] + dev->value[2] + dev->value[3];
	
	if(tmp != dev->value[4]){
		printk(KERN_INFO "[%s] %d %d\n", __func__, dev->value[4], tmp);
		return -1;
	}
	return 1;
}

static int dht11_sensor_open(struct inode *inode, struct file *filp)
{
	printk("dht11_sensor_open\n");	
	return 0;
}

static ssize_t dht11_sensor_read(struct file *filp,char __user *buf,size_t size,loff_t *f_pos)
{
	int result = 0;
	dht11_dev->started = 0;
	dht11_dev->bitcount = 0;
	dht11_dev->bytecount = 0;
	dht11_dev->value[0] = 0;
	dht11_dev->value[1] = 0;
	dht11_dev->value[2] = 0;
	dht11_dev->value[3] = 0;
	dht11_dev->value[4] = 0;
 
	dht11_start();
	dht11_setup_interrupts();
	msleep(10);
	dht11_clear_interrupts(); 
	result=dht11_checksum(dht11_dev);
	if(result<0)
			return -EAGAIN; 

	printk("Humidity=%d.%d%%---Temperature=%d.%dC\n",\
			dht11_dev->value[0], dht11_dev->value[1], \
			dht11_dev->value[2], dht11_dev->value[3]);
	printk("count =%d\n",dht11_dev->count);
    result=copy_to_user(buf,&dht11_dev->value,4);
    if(result<0)
	{
         printk("copy to user err\n");
         return -EAGAIN;
    } 
    return  result;           
}

static int dht11_sensor_release(struct inode *inode,struct file *filp)
{
	module_put(THIS_MODULE);
	return 0;
}

static struct file_operations dht11_sensor_fops={
	.owner   = THIS_MODULE,
	.open    = dht11_sensor_open,
	.read    = dht11_sensor_read,
	.release = dht11_sensor_release,
};

static int dht11_gpio_init(void)
{
	int result;
	dht11_dev->pin = DHT11_PIN;
    result=gpio_request(dht11_dev->pin, DEVICE_NAME);
	if(result)
	{
		printk(KERN_INFO "[%s] gpio_request \n", __func__);
		return -1;
	}
	gpio_direction_output(dht11_dev->pin,1);
	gpio_free(dht11_dev->pin);
	return 0;
}

static int dht11_sensor_setup_cdev(void)
{
	int ret;
	cdev_init(&(dht11_dev->cdev), &dht11_sensor_fops);
	dht11_dev->cdev.owner = THIS_MODULE;
	ret=cdev_add(&(dht11_dev->cdev),dht11_dev->devno, 1);
	if(ret)
	{
		printk(KERN_NOTICE"erro %d adding %s\n",ret,DEVICE_NAME);
	}
	return ret;
}

int __init dht11_sensor_init(void)
{
	int result;
	dht11_dev=kmalloc(sizeof(struct dht11_sensor_dev),GFP_KERNEL);
	if(!dht11_dev)
	{
		result=-ENOMEM;
		goto allocate_memory_fail;
	}
    if(DEVICE_MAJOR)
	{
		result = register_chrdev_region(dht11_dev->devno, 1, DEVICE_NAME);
	}
	else
	{
		result = alloc_chrdev_region(&dht11_dev->devno, 0, 1, DEVICE_NAME);
	}
	if(result < 0)
	{
	    printk("register_chrdev_region err!\n");
		goto chardev_region_fail;
	}
	dht11_dev->dht11_class = class_create(THIS_MODULE, DEVICE_NAME);
	if(IS_ERR(dht11_dev->dht11_class))
    {
             printk("Err: failed in creating class.\n");
             goto class_create_fail;
    } 
	device_create(dht11_dev->dht11_class, NULL,dht11_dev->devno, NULL, DEVICE_NAME);
	result=dht11_sensor_setup_cdev();
	if(result<0)
		goto cdev_fail;
	result=dht11_gpio_init();
	if(result<0)
		goto gpio_request_fail;
	INIT_WORK(&dht11_dev->dht11_work,dht11_data_factory);
	mutex_init(&dht11_dev->read_data);
	printk("dht11 init ok!\n");
	return 0;
	
gpio_request_fail:
	cdev_del(&dht11_dev->cdev);
cdev_fail:
	device_destroy(dht11_dev->dht11_class,dht11_dev->devno);
	class_destroy(dht11_dev->dht11_class);
class_create_fail:
	unregister_chrdev_region(dht11_dev->devno,1);
chardev_region_fail:
allocate_memory_fail:
	kfree(dht11_dev);
	return result;
}

void  __exit dht11_sensor_exit(void)
{
	cdev_del(&dht11_dev->cdev);
	device_destroy(dht11_dev->dht11_class,dht11_dev->devno);
	class_destroy(dht11_dev->dht11_class);	
	unregister_chrdev_region(dht11_dev->devno, 1);
	kfree(dht11_dev);
}

module_init(dht11_sensor_init);
module_exit(dht11_sensor_exit);

MODULE_AUTHOR("jvaemape");
MODULE_DESCRIPTION("DHT11 Driver");
MODULE_LICENSE("Dual BSD/GPL");

其实，高版本的内核中已集成湿度传感器的驱动，可以研究一下https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/drivers/iio/humidity/dht11.c?id=refs/tags/v4.5

源码摘录如下

/*
 * DHT11/DHT22 bit banging GPIO driver
 *
 * Copyright (c) Harald Geyer <harald@ccbib.org>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 */

#include <linux/err.h>
#include <linux/interrupt.h>
#include <linux/device.h>
#include <linux/kernel.h>
#include <linux/printk.h>
#include <linux/slab.h>
#include <linux/of.h>
#include <linux/of_device.h>
#include <linux/sysfs.h>
#include <linux/io.h>
#include <linux/module.h>
#include <linux/platform_device.h>
#include <linux/wait.h>
#include <linux/bitops.h>
#include <linux/completion.h>
#include <linux/mutex.h>
#include <linux/delay.h>
#include <linux/gpio.h>
#include <linux/of_gpio.h>
#include <linux/timekeeping.h>

#include <linux/iio/iio.h>

#define DRIVER_NAME	"dht11"

#define DHT11_DATA_VALID_TIME	2000000000  /* 2s in ns */

#define DHT11_EDGES_PREAMBLE 2
#define DHT11_BITS_PER_READ 40
/*
 * Note that when reading the sensor actually 84 edges are detected, but
 * since the last edge is not significant, we only store 83:
 */
#define DHT11_EDGES_PER_READ (2 * DHT11_BITS_PER_READ + \
			      DHT11_EDGES_PREAMBLE + 1)

/* Data transmission timing (nano seconds) */
#define DHT11_START_TRANSMISSION	18  /* ms */
#define DHT11_SENSOR_RESPONSE	80000
#define DHT11_START_BIT		50000
#define DHT11_DATA_BIT_LOW	27000
#define DHT11_DATA_BIT_HIGH	70000

struct dht11 {
	struct device			*dev;

	int				gpio;
	int				irq;

	struct completion		completion;
	/* The iio sysfs interface doesn't prevent concurrent reads: */
	struct mutex			lock;

	s64				timestamp;
	int				temperature;
	int				humidity;

	/* num_edges: -1 means "no transmission in progress" */
	int				num_edges;
	struct {s64 ts; int value; }	edges[DHT11_EDGES_PER_READ];
};

static unsigned char dht11_decode_byte(int *timing, int threshold)
{
	unsigned char ret = 0;
	int i;

	for (i = 0; i < 8; ++i) {
		ret <<= 1;
		if (timing[i] >= threshold)
			++ret;
	}

	return ret;
}

static int dht11_decode(struct dht11 *dht11, int offset, int timeres)
{
	int i, t, timing[DHT11_BITS_PER_READ], threshold;
	unsigned char temp_int, temp_dec, hum_int, hum_dec, checksum;

	threshold = DHT11_DATA_BIT_HIGH / timeres;
	if (DHT11_DATA_BIT_LOW / timeres + 1 >= threshold)
		pr_err("dht11: WARNING: decoding ambiguous\n");

	/* scale down with timeres and check validity */
	for (i = 0; i < DHT11_BITS_PER_READ; ++i) {
		t = dht11->edges[offset + 2 * i + 2].ts -
			dht11->edges[offset + 2 * i + 1].ts;
		if (!dht11->edges[offset + 2 * i + 1].value)
			return -EIO;  /* lost synchronisation */
		timing[i] = t / timeres;
	}

	hum_int = dht11_decode_byte(timing, threshold);
	hum_dec = dht11_decode_byte(&timing[8], threshold);
	temp_int = dht11_decode_byte(&timing[16], threshold);
	temp_dec = dht11_decode_byte(&timing[24], threshold);
	checksum = dht11_decode_byte(&timing[32], threshold);

	if (((hum_int + hum_dec + temp_int + temp_dec) & 0xff) != checksum)
		return -EIO;

	dht11->timestamp = ktime_get_boot_ns();
	if (hum_int < 20) {  /* DHT22 */
		dht11->temperature = (((temp_int & 0x7f) << 8) + temp_dec) *
					((temp_int & 0x80) ? -100 : 100);
		dht11->humidity = ((hum_int << 8) + hum_dec) * 100;
	} else if (temp_dec == 0 && hum_dec == 0) {  /* DHT11 */
		dht11->temperature = temp_int * 1000;
		dht11->humidity = hum_int * 1000;
	} else {
		dev_err(dht11->dev,
			"Don't know how to decode data: %d %d %d %d\n",
			hum_int, hum_dec, temp_int, temp_dec);
		return -EIO;
	}

	return 0;
}

/*
 * IRQ handler called on GPIO edges
 */
static irqreturn_t dht11_handle_irq(int irq, void *data)
{
	struct iio_dev *iio = data;
	struct dht11 *dht11 = iio_priv(iio);

	/* TODO: Consider making the handler safe for IRQ sharing */
	if (dht11->num_edges < DHT11_EDGES_PER_READ && dht11->num_edges >= 0) {
		dht11->edges[dht11->num_edges].ts = ktime_get_boot_ns();
		dht11->edges[dht11->num_edges++].value =
						gpio_get_value(dht11->gpio);

		if (dht11->num_edges >= DHT11_EDGES_PER_READ)
			complete(&dht11->completion);
	}

	return IRQ_HANDLED;
}

static int dht11_read_raw(struct iio_dev *iio_dev,
			  const struct iio_chan_spec *chan,
			int *val, int *val2, long m)
{
	struct dht11 *dht11 = iio_priv(iio_dev);
	int ret, timeres;

	mutex_lock(&dht11->lock);
	if (dht11->timestamp + DHT11_DATA_VALID_TIME < ktime_get_boot_ns()) {
		timeres = ktime_get_resolution_ns();
		if (DHT11_DATA_BIT_HIGH < 2 * timeres) {
			dev_err(dht11->dev, "timeresolution %dns too low\n",
				timeres);
			/* In theory a better clock could become available
			 * at some point ... and there is no error code
			 * that really fits better.
			 */
			ret = -EAGAIN;
			goto err;
		}

		reinit_completion(&dht11->completion);

		dht11->num_edges = 0;
		ret = gpio_direction_output(dht11->gpio, 0);
		if (ret)
			goto err;
		msleep(DHT11_START_TRANSMISSION);
		ret = gpio_direction_input(dht11->gpio);
		if (ret)
			goto err;

		ret = request_irq(dht11->irq, dht11_handle_irq,
				  IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING,
				  iio_dev->name, iio_dev);
		if (ret)
			goto err;

		ret = wait_for_completion_killable_timeout(&dht11->completion,
							   HZ);

		free_irq(dht11->irq, iio_dev);

		if (ret == 0 && dht11->num_edges < DHT11_EDGES_PER_READ - 1) {
			dev_err(&iio_dev->dev,
				"Only %d signal edges detected\n",
					dht11->num_edges);
			ret = -ETIMEDOUT;
		}
		if (ret < 0)
			goto err;

		ret = dht11_decode(dht11,
				   dht11->num_edges == DHT11_EDGES_PER_READ ?
					DHT11_EDGES_PREAMBLE :
					DHT11_EDGES_PREAMBLE - 2,
				timeres);
		if (ret)
			goto err;
	}

	ret = IIO_VAL_INT;
	if (chan->type == IIO_TEMP)
		*val = dht11->temperature;
	else if (chan->type == IIO_HUMIDITYRELATIVE)
		*val = dht11->humidity;
	else
		ret = -EINVAL;
err:
	dht11->num_edges = -1;
	mutex_unlock(&dht11->lock);
	return ret;
}

static const struct iio_info dht11_iio_info = {
	.driver_module		= THIS_MODULE,
	.read_raw		= dht11_read_raw,
};

static const struct iio_chan_spec dht11_chan_spec[] = {
	{ .type = IIO_TEMP,
		.info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), },
	{ .type = IIO_HUMIDITYRELATIVE,
		.info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), }
};

static const struct of_device_id dht11_dt_ids[] = {
	{ .compatible = "dht11", },
	{ }
};
MODULE_DEVICE_TABLE(of, dht11_dt_ids);

static int dht11_probe(struct platform_device *pdev)
{
	struct device *dev = &pdev->dev;
	struct device_node *node = dev->of_node;
	struct dht11 *dht11;
	struct iio_dev *iio;
	int ret;

	iio = devm_iio_device_alloc(dev, sizeof(*dht11));
	if (!iio) {
		dev_err(dev, "Failed to allocate IIO device\n");
		return -ENOMEM;
	}

	dht11 = iio_priv(iio);
	dht11->dev = dev;

	ret = of_get_gpio(node, 0);
	if (ret < 0)
		return ret;
	dht11->gpio = ret;
	ret = devm_gpio_request_one(dev, dht11->gpio, GPIOF_IN, pdev->name);
	if (ret)
		return ret;

	dht11->irq = gpio_to_irq(dht11->gpio);
	if (dht11->irq < 0) {
		dev_err(dev, "GPIO %d has no interrupt\n", dht11->gpio);
		return -EINVAL;
	}

	dht11->timestamp = ktime_get_boot_ns() - DHT11_DATA_VALID_TIME - 1;
	dht11->num_edges = -1;

	platform_set_drvdata(pdev, iio);

	init_completion(&dht11->completion);
	mutex_init(&dht11->lock);
	iio->name = pdev->name;
	iio->dev.parent = &pdev->dev;
	iio->info = &dht11_iio_info;
	iio->modes = INDIO_DIRECT_MODE;
	iio->channels = dht11_chan_spec;
	iio->num_channels = ARRAY_SIZE(dht11_chan_spec);

	return devm_iio_device_register(dev, iio);
}

static struct platform_driver dht11_driver = {
	.driver = {
		.name	= DRIVER_NAME,
		.of_match_table = dht11_dt_ids,
	},
	.probe  = dht11_probe,
};

module_platform_driver(dht11_driver);

MODULE_AUTHOR("Harald Geyer <harald@ccbib.org>");
MODULE_DESCRIPTION("DHT11 humidity/temperature sensor driver");
MODULE_LICENSE("GPL v2");