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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: Harald Geyer <harald@ccbib.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
This commit is contained in:
Harald Geyer 2015-07-07 13:39:31 +00:00 committed by Jonathan Cameron
parent 5fbb0bc466
commit 081d974031
1 changed files with 22 additions and 20 deletions
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42
drivers/iio/humidity/dht11.c
View File

@ -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);