linux-imx

/*

 * 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:

 * Data bits are encoded as pulse length (high time) on the data line.

 * 0-bit: 22-30uS -- typically 26uS (AM2302)

 * 1-bit: 68-75uS -- typically 70uS (AM2302)

 * The acutal timings also depend on the properties of the cable, with

 * longer cables typically making pulses shorter.

 *

 * Our decoding depends on the time resolution of the system:

 * timeres > 34uS ... don't know what a 1-tick pulse is

 * 34uS > timeres > 30uS ... no problem (30kHz and 32kHz clocks)

 * 30uS > timeres > 23uS ... don't know what a 2-tick pulse is

 * timeres < 23uS ... no problem

 *

 * Luckily clocks in the 33-44kHz range are quite uncommon, so we can

 * support most systems if the threshold for decoding a pulse as 1-bit

 * is chosen carefully. If somebody really wants to support clocks around

 * 40kHz, where this driver is most unreliable, there are two options.

 * a) select an implementation using busy loop polling on those systems

 * b) use the checksum to do some probabilistic decoding

 */

#define DHT11_START_TRANSMISSION_MIN    18000  /* us */

#define DHT11_START_TRANSMISSION_MAX    20000  /* us */

#define DHT11_MIN_TIMERES   34000  /* ns */

#define DHT11_THRESHOLD     49000  /* ns */

#define DHT11_AMBIG_LOW     23000  /* ns */

#define DHT11_AMBIG_HIGH    30000  /* ns */

​

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;