// SPDX-License-Identifier: GPL-2.0-or-later
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/*
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* DHT11/DHT22 bit banging GPIO driver
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*
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* Copyright (c) Harald Geyer <harald@ccbib.org>
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*/
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#include <linux/err.h>
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#include <linux/interrupt.h>
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#include <linux/device.h>
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#include <linux/kernel.h>
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#include <linux/printk.h>
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#include <linux/slab.h>
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#include <linux/of.h>
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#include <linux/of_device.h>
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#include <linux/sysfs.h>
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#include <linux/io.h>
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#include <linux/module.h>
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#include <linux/platform_device.h>
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#include <linux/wait.h>
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#include <linux/bitops.h>
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#include <linux/completion.h>
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#include <linux/mutex.h>
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#include <linux/delay.h>
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#include <linux/gpio/consumer.h>
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#include <linux/timekeeping.h>
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#include <linux/iio/iio.h>
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#define DRIVER_NAME "dht11"
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#define DHT11_DATA_VALID_TIME 2000000000 /* 2s in ns */
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#define DHT11_EDGES_PREAMBLE 2
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#define DHT11_BITS_PER_READ 40
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/*
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* Note that when reading the sensor actually 84 edges are detected, but
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* since the last edge is not significant, we only store 83:
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*/
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#define DHT11_EDGES_PER_READ (2 * DHT11_BITS_PER_READ + \
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DHT11_EDGES_PREAMBLE + 1)
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/*
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* Data transmission timing:
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* Data bits are encoded as pulse length (high time) on the data line.
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* 0-bit: 22-30uS -- typically 26uS (AM2302)
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* 1-bit: 68-75uS -- typically 70uS (AM2302)
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* The acutal timings also depend on the properties of the cable, with
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* longer cables typically making pulses shorter.
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*
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* Our decoding depends on the time resolution of the system:
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* timeres > 34uS ... don't know what a 1-tick pulse is
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* 34uS > timeres > 30uS ... no problem (30kHz and 32kHz clocks)
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* 30uS > timeres > 23uS ... don't know what a 2-tick pulse is
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* timeres < 23uS ... no problem
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*
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* Luckily clocks in the 33-44kHz range are quite uncommon, so we can
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* support most systems if the threshold for decoding a pulse as 1-bit
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* is chosen carefully. If somebody really wants to support clocks around
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* 40kHz, where this driver is most unreliable, there are two options.
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* a) select an implementation using busy loop polling on those systems
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* b) use the checksum to do some probabilistic decoding
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*/
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#define DHT11_START_TRANSMISSION_MIN 18000 /* us */
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#define DHT11_START_TRANSMISSION_MAX 20000 /* us */
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#define DHT11_MIN_TIMERES 34000 /* ns */
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#define DHT11_THRESHOLD 49000 /* ns */
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#define DHT11_AMBIG_LOW 23000 /* ns */
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#define DHT11_AMBIG_HIGH 30000 /* ns */
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struct dht11 {
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struct device *dev;
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struct gpio_desc *gpiod;
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int irq;
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struct completion completion;
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/* The iio sysfs interface doesn't prevent concurrent reads: */
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struct mutex lock;
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s64 timestamp;
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int temperature;
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int humidity;
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/* num_edges: -1 means "no transmission in progress" */
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int num_edges;
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struct {s64 ts; int value; } edges[DHT11_EDGES_PER_READ];
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};
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#ifdef CONFIG_DYNAMIC_DEBUG
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/*
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* dht11_edges_print: show the data as actually received by the
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* driver.
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*/
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static void dht11_edges_print(struct dht11 *dht11)
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{
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int i;
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dev_dbg(dht11->dev, "%d edges detected:\n", dht11->num_edges);
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for (i = 1; i < dht11->num_edges; ++i) {
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dev_dbg(dht11->dev, "%d: %lld ns %s\n", i,
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dht11->edges[i].ts - dht11->edges[i - 1].ts,
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dht11->edges[i - 1].value ? "high" : "low");
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}
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}
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#endif /* CONFIG_DYNAMIC_DEBUG */
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static unsigned char dht11_decode_byte(char *bits)
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{
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unsigned char ret = 0;
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int i;
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for (i = 0; i < 8; ++i) {
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ret <<= 1;
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if (bits[i])
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++ret;
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}
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return ret;
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}
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static int dht11_decode(struct dht11 *dht11, int offset)
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{
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int i, t;
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char bits[DHT11_BITS_PER_READ];
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unsigned char temp_int, temp_dec, hum_int, hum_dec, checksum;
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for (i = 0; i < DHT11_BITS_PER_READ; ++i) {
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t = dht11->edges[offset + 2 * i + 2].ts -
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dht11->edges[offset + 2 * i + 1].ts;
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if (!dht11->edges[offset + 2 * i + 1].value) {
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dev_dbg(dht11->dev,
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"lost synchronisation at edge %d\n",
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offset + 2 * i + 1);
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return -EIO;
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}
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bits[i] = t > DHT11_THRESHOLD;
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}
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hum_int = dht11_decode_byte(bits);
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hum_dec = dht11_decode_byte(&bits[8]);
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temp_int = dht11_decode_byte(&bits[16]);
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temp_dec = dht11_decode_byte(&bits[24]);
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checksum = dht11_decode_byte(&bits[32]);
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if (((hum_int + hum_dec + temp_int + temp_dec) & 0xff) != checksum) {
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dev_dbg(dht11->dev, "invalid checksum\n");
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return -EIO;
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}
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dht11->timestamp = ktime_get_boottime_ns();
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if (hum_int < 4) { /* DHT22: 100000 = (3*256+232)*100 */
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dht11->temperature = (((temp_int & 0x7f) << 8) + temp_dec) *
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((temp_int & 0x80) ? -100 : 100);
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dht11->humidity = ((hum_int << 8) + hum_dec) * 100;
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} else if (temp_dec == 0 && hum_dec == 0) { /* DHT11 */
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dht11->temperature = temp_int * 1000;
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dht11->humidity = hum_int * 1000;
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} else {
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dev_err(dht11->dev,
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"Don't know how to decode data: %d %d %d %d\n",
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hum_int, hum_dec, temp_int, temp_dec);
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return -EIO;
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}
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return 0;
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}
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/*
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* IRQ handler called on GPIO edges
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*/
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static irqreturn_t dht11_handle_irq(int irq, void *data)
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{
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struct iio_dev *iio = data;
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struct dht11 *dht11 = iio_priv(iio);
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if (dht11->num_edges < DHT11_EDGES_PER_READ && dht11->num_edges >= 0) {
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dht11->edges[dht11->num_edges].ts = ktime_get_boottime_ns();
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dht11->edges[dht11->num_edges++].value =
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gpiod_get_value(dht11->gpiod);
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if (dht11->num_edges >= DHT11_EDGES_PER_READ)
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complete(&dht11->completion);
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}
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return IRQ_HANDLED;
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}
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static int dht11_read_raw(struct iio_dev *iio_dev,
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const struct iio_chan_spec *chan,
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int *val, int *val2, long m)
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{
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struct dht11 *dht11 = iio_priv(iio_dev);
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int ret, timeres, offset;
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mutex_lock(&dht11->lock);
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if (dht11->timestamp + DHT11_DATA_VALID_TIME < ktime_get_boottime_ns()) {
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timeres = ktime_get_resolution_ns();
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dev_dbg(dht11->dev, "current timeresolution: %dns\n", timeres);
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if (timeres > DHT11_MIN_TIMERES) {
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dev_err(dht11->dev, "timeresolution %dns too low\n",
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timeres);
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/* In theory a better clock could become available
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* at some point ... and there is no error code
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* that really fits better.
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*/
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ret = -EAGAIN;
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goto err;
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}
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if (timeres > DHT11_AMBIG_LOW && timeres < DHT11_AMBIG_HIGH)
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dev_warn(dht11->dev,
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"timeresolution: %dns - decoding ambiguous\n",
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timeres);
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reinit_completion(&dht11->completion);
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dht11->num_edges = 0;
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ret = gpiod_direction_output(dht11->gpiod, 0);
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if (ret)
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goto err;
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usleep_range(DHT11_START_TRANSMISSION_MIN,
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DHT11_START_TRANSMISSION_MAX);
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ret = gpiod_direction_input(dht11->gpiod);
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if (ret)
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goto err;
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ret = request_irq(dht11->irq, dht11_handle_irq,
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IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING,
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iio_dev->name, iio_dev);
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if (ret)
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goto err;
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ret = wait_for_completion_killable_timeout(&dht11->completion,
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HZ);
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free_irq(dht11->irq, iio_dev);
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#ifdef CONFIG_DYNAMIC_DEBUG
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dht11_edges_print(dht11);
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#endif
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if (ret == 0 && dht11->num_edges < DHT11_EDGES_PER_READ - 1) {
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dev_err(dht11->dev, "Only %d signal edges detected\n",
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dht11->num_edges);
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ret = -ETIMEDOUT;
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}
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if (ret < 0)
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goto err;
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offset = DHT11_EDGES_PREAMBLE +
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dht11->num_edges - DHT11_EDGES_PER_READ;
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for (; offset >= 0; --offset) {
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ret = dht11_decode(dht11, offset);
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if (!ret)
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break;
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}
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if (ret)
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goto err;
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}
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ret = IIO_VAL_INT;
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if (chan->type == IIO_TEMP)
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*val = dht11->temperature;
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else if (chan->type == IIO_HUMIDITYRELATIVE)
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*val = dht11->humidity;
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else
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ret = -EINVAL;
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err:
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dht11->num_edges = -1;
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mutex_unlock(&dht11->lock);
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return ret;
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}
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static const struct iio_info dht11_iio_info = {
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.read_raw = dht11_read_raw,
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};
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static const struct iio_chan_spec dht11_chan_spec[] = {
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{ .type = IIO_TEMP,
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.info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), },
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{ .type = IIO_HUMIDITYRELATIVE,
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.info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), }
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};
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static const struct of_device_id dht11_dt_ids[] = {
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{ .compatible = "dht11", },
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{ }
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};
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MODULE_DEVICE_TABLE(of, dht11_dt_ids);
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static int dht11_probe(struct platform_device *pdev)
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{
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struct device *dev = &pdev->dev;
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struct dht11 *dht11;
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struct iio_dev *iio;
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iio = devm_iio_device_alloc(dev, sizeof(*dht11));
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if (!iio) {
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dev_err(dev, "Failed to allocate IIO device\n");
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return -ENOMEM;
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}
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dht11 = iio_priv(iio);
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dht11->dev = dev;
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dht11->gpiod = devm_gpiod_get(dev, NULL, GPIOD_IN);
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if (IS_ERR(dht11->gpiod))
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return PTR_ERR(dht11->gpiod);
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dht11->irq = gpiod_to_irq(dht11->gpiod);
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if (dht11->irq < 0) {
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dev_err(dev, "GPIO %d has no interrupt\n", desc_to_gpio(dht11->gpiod));
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return -EINVAL;
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}
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dht11->timestamp = ktime_get_boottime_ns() - DHT11_DATA_VALID_TIME - 1;
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dht11->num_edges = -1;
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platform_set_drvdata(pdev, iio);
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init_completion(&dht11->completion);
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mutex_init(&dht11->lock);
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iio->name = pdev->name;
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iio->info = &dht11_iio_info;
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iio->modes = INDIO_DIRECT_MODE;
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iio->channels = dht11_chan_spec;
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iio->num_channels = ARRAY_SIZE(dht11_chan_spec);
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return devm_iio_device_register(dev, iio);
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}
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static struct platform_driver dht11_driver = {
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.driver = {
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.name = DRIVER_NAME,
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.of_match_table = dht11_dt_ids,
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},
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.probe = dht11_probe,
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};
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module_platform_driver(dht11_driver);
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MODULE_AUTHOR("Harald Geyer <harald@ccbib.org>");
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MODULE_DESCRIPTION("DHT11 humidity/temperature sensor driver");
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MODULE_LICENSE("GPL v2");
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