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Commit 081d9740 authored by Harald Geyer's avatar Harald Geyer Committed by Jonathan Cameron
Browse files

iio: dht11: Use new function ktime_get_resolution_ns() 



This cleans up the most ugly workaround in this driver. There are no
functional changes yet in the decoding algorithm, but we improve the
following things:
 * Get rid of spurious warning messages on systems with fast HRTIMER.
 * If the clock is not fast enough for decoding to work, we give
   up immediately.
 * In that case we return EAGAIN instead of EIO, so it's easier to
   discriminate causes of failure.

Returning EAGAIN is somewhat controversial: It's technically correct
as a faster clock might become available. OTOH once all clocks are
enabled this is a permanent error. There is no ECLOCKTOOSLOW error
code.

Signed-off-by: default avatarHarald Geyer <harald@ccbib.org>
Signed-off-by: default avatarJonathan Cameron <jic23@kernel.org>
parent 5fbb0bc4

drivers/iio/humidity/dht11.c

+22 −20
Original line number Original line Diff line number Diff line
@@ -33,6 +33,7 @@ 
#include <linux/delay.h>

#include <linux/delay.h>

#include <linux/gpio.h>

#include <linux/gpio.h>

#include <linux/of_gpio.h>

#include <linux/of_gpio.h>

#include <linux/timekeeping.h>





#include <linux/iio/iio.h>

#include <linux/iio/iio.h>
@@ -89,23 +90,11 @@ static unsigned char dht11_decode_byte(int *timing, int threshold) 
	return ret;

	return ret;

}

}





static int dht11_decode(struct dht11 *dht11, int offset)

static int dht11_decode(struct dht11 *dht11, int offset, int timeres)

{

{

	int i, t, timing[DHT11_BITS_PER_READ], threshold,

	int i, t, timing[DHT11_BITS_PER_READ], threshold;

		timeres = DHT11_SENSOR_RESPONSE;

	unsigned char temp_int, temp_dec, hum_int, hum_dec, checksum;

	unsigned char temp_int, temp_dec, hum_int, hum_dec, checksum;





	/* Calculate timestamp resolution */

	for (i = 1; i < dht11->num_edges; ++i) {

		t = dht11->edges[i].ts - dht11->edges[i - 1].ts;

		if (t > 0 && t < timeres)

			timeres = t;

	}

	if (2 * timeres > DHT11_DATA_BIT_HIGH) {

		pr_err("dht11: timeresolution %d too bad for decoding\n",

		       timeres);

		return -EIO;

	}

	threshold = DHT11_DATA_BIT_HIGH / timeres;

	threshold = DHT11_DATA_BIT_HIGH / timeres;

	if (DHT11_DATA_BIT_LOW / timeres + 1 >= threshold)

	if (DHT11_DATA_BIT_LOW / timeres + 1 >= threshold)

		pr_err("dht11: WARNING: decoding ambiguous\n");

		pr_err("dht11: WARNING: decoding ambiguous\n");
@@ -128,7 +117,7 @@ static int dht11_decode(struct dht11 *dht11, int offset) 
	if (((hum_int + hum_dec + temp_int + temp_dec) & 0xff) != checksum)

	if (((hum_int + hum_dec + temp_int + temp_dec) & 0xff) != checksum)

		return -EIO;

		return -EIO;





	dht11->timestamp = iio_get_time_ns();

	dht11->timestamp = ktime_get_real_ns();

	if (hum_int < 20) {  /* DHT22 */

	if (hum_int < 20) {  /* DHT22 */

		dht11->temperature = (((temp_int & 0x7f) << 8) + temp_dec) *

		dht11->temperature = (((temp_int & 0x7f) << 8) + temp_dec) *

					((temp_int & 0x80) ? -100 : 100);

					((temp_int & 0x80) ? -100 : 100);
@@ -156,7 +145,7 @@ static irqreturn_t dht11_handle_irq(int irq, void *data) 




	/* TODO: Consider making the handler safe for IRQ sharing */

	/* TODO: Consider making the handler safe for IRQ sharing */

	if (dht11->num_edges < DHT11_EDGES_PER_READ && dht11->num_edges >= 0) {

	if (dht11->num_edges < DHT11_EDGES_PER_READ && dht11->num_edges >= 0) {

		dht11->edges[dht11->num_edges].ts = iio_get_time_ns();

		dht11->edges[dht11->num_edges].ts = ktime_get_real_ns();

		dht11->edges[dht11->num_edges++].value =

		dht11->edges[dht11->num_edges++].value =

						gpio_get_value(dht11->gpio);

						gpio_get_value(dht11->gpio);
@@ -172,10 +161,22 @@ static int dht11_read_raw(struct iio_dev *iio_dev, 
			int *val, int *val2, long m)

			int *val, int *val2, long m)

{

{

	struct dht11 *dht11 = iio_priv(iio_dev);

	struct dht11 *dht11 = iio_priv(iio_dev);

	int ret;

	int ret, timeres;





	mutex_lock(&dht11->lock);

	mutex_lock(&dht11->lock);

	if (dht11->timestamp + DHT11_DATA_VALID_TIME < iio_get_time_ns()) {

	if (dht11->timestamp + DHT11_DATA_VALID_TIME < ktime_get_real_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);

		reinit_completion(&dht11->completion);





		dht11->num_edges = 0;

		dht11->num_edges = 0;
@@ -210,7 +211,8 @@ static int dht11_read_raw(struct iio_dev *iio_dev, 
		ret = dht11_decode(dht11,

		ret = dht11_decode(dht11,

				   dht11->num_edges == DHT11_EDGES_PER_READ ?

				   dht11->num_edges == DHT11_EDGES_PER_READ ?

					DHT11_EDGES_PREAMBLE :

					DHT11_EDGES_PREAMBLE :

					DHT11_EDGES_PREAMBLE - 2);

					DHT11_EDGES_PREAMBLE - 2,

				timeres);

		if (ret)

		if (ret)

			goto err;

			goto err;

	}

	}
@@ -277,7 +279,7 @@ static int dht11_probe(struct platform_device *pdev) 
		return -EINVAL;

		return -EINVAL;

	}

	}





	dht11->timestamp = iio_get_time_ns() - DHT11_DATA_VALID_TIME - 1;

	dht11->timestamp = ktime_get_real_ns() - DHT11_DATA_VALID_TIME - 1;

	dht11->num_edges = -1;

	dht11->num_edges = -1;





	platform_set_drvdata(pdev, iio);

	platform_set_drvdata(pdev, iio);