// SPDX-License-Identifier: GPL-2.0-or-later /* * DHT11/DHT22 bit banging GPIO driver * * Copyright (c) Harald Geyer <[email protected]> */ #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/sysfs.h> #include <linux/io.h> #include <linux/mod_devicetable.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/consumer.h> #include <linux/timekeeping.h> #include <linux/iio/iio.h> #define DRIVER_NAME … #define DHT11_DATA_VALID_TIME … #define DHT11_EDGES_PREAMBLE … #define DHT11_BITS_PER_READ … /* * 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 … /* * 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 … #define DHT11_START_TRANSMISSION_MAX … #define DHT11_MIN_TIMERES … #define DHT11_THRESHOLD … #define DHT11_AMBIG_LOW … #define DHT11_AMBIG_HIGH … struct dht11 { … }; #ifdef CONFIG_DYNAMIC_DEBUG /* * dht11_edges_print: show the data as actually received by the * driver. */ static void dht11_edges_print(struct dht11 *dht11) { … } #endif /* CONFIG_DYNAMIC_DEBUG */ static unsigned char dht11_decode_byte(char *bits) { … } static int dht11_decode(struct dht11 *dht11, int offset) { … } /* * IRQ handler called on GPIO edges */ static irqreturn_t dht11_handle_irq(int irq, void *data) { … } static int dht11_read_raw(struct iio_dev *iio_dev, const struct iio_chan_spec *chan, int *val, int *val2, long m) { … } static const struct iio_info dht11_iio_info = …; static const struct iio_chan_spec dht11_chan_spec[] = …; static const struct of_device_id dht11_dt_ids[] = …; MODULE_DEVICE_TABLE(of, dht11_dt_ids); static int dht11_probe(struct platform_device *pdev) { … } static struct platform_driver dht11_driver = …; module_platform_driver(…) …; MODULE_AUTHOR(…) …; MODULE_DESCRIPTION(…) …; MODULE_LICENSE(…) …;
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