The Si7013/20/21 modules support 2 read modes:
* Hold mode, where the device stretches the clock until the end of the
measurement
* No Hold mode, where the device replies NACK for every I2C call during
the measurement
Here the No Hold mode is implemented, selectable with the boolean
parameter holdmode=N. The No Hold mode is less efficient, since it
requires multiple calls to the device, but it can be used as a fallback if
the clock stretching is not supported.
Signed-off-by: Nicola Corna <nicola@xxxxxxxxxx>
---
I've tested this on a Raspberry Pi 2, where the clock stretching is
currently bugged.
drivers/iio/humidity/si7020.c | 55 +++++++++++++++++++++++++++++++++++++------
1 file changed, 48 insertions(+), 7 deletions(-)
diff --git a/drivers/iio/humidity/si7020.c b/drivers/iio/humidity/si7020.c
index 62fdbcf..a8bad04 100644
--- a/drivers/iio/humidity/si7020.c
+++ b/drivers/iio/humidity/si7020.c
@@ -2,6 +2,7 @@
* si7020.c - Silicon Labs Si7013/20/21 Relative Humidity and Temp Sensors
* Copyright (c) 2013,2014 Uplogix, Inc.
* David Barksdale <dbarksdale@xxxxxxxxxxx>
+ * Copyright (c) 2015 Nicola Corna <nicola@xxxxxxxxxx>
*
* This program is free software; you can redistribute it and/or modify it
* under the terms and conditions of the GNU General Public License,
@@ -30,16 +31,33 @@
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/sysfs.h>
+#include <linux/jiffies.h>
#include <linux/iio/iio.h>
#include <linux/iio/sysfs.h>
/* Measure Relative Humidity, Hold Master Mode */
#define SI7020CMD_RH_HOLD 0xE5
+/* Measure Relative Humidity, No Hold Master Mode */
+#define SI7020CMD_RH_NO_HOLD 0xF5
/* Measure Temperature, Hold Master Mode */
#define SI7020CMD_TEMP_HOLD 0xE3
+/* Measure Temperature, No Hold Master Mode */
+#define SI7020CMD_TEMP_NO_HOLD 0xF3
/* Software Reset */
#define SI7020CMD_RESET 0xFE
+/* Relative humidity measurement timeout (us) */
+#define SI7020_RH_TIMEOUT 22800
+/* Temperature measurement timeout (us) */
+#define SI7020_TEMP_TIMEOUT 10800
+/* Minimum delay between retries (No Hold Mode) in us */
+#define SI7020_NOHOLD_SLEEP_MIN 2000
+/* Maximum delay between retries (No Hold Mode) in us */
+#define SI7020_NOHOLD_SLEEP_MAX 6000
+
+static bool holdmode = 1;
+module_param(holdmode, bool, 0644);
+MODULE_PARM_DESC(holdmode, "Select whether the measurement has to be done with Hold Mode (clock stretching) or No Hold Mode (repeated calls)");
static int si7020_read_raw(struct iio_dev *indio_dev,
struct iio_chan_spec const *chan, int *val,
@@ -47,16 +65,39 @@ static int si7020_read_raw(struct iio_dev *indio_dev,
{
struct i2c_client **client = iio_priv(indio_dev);
int ret;
+ unsigned char buf[2];
+ unsigned long start;
switch (mask) {
case IIO_CHAN_INFO_RAW:
- ret = i2c_smbus_read_word_data(*client,
- chan->type == IIO_TEMP ?
- SI7020CMD_TEMP_HOLD :
- SI7020CMD_RH_HOLD);
- if (ret < 0)
- return ret;
- *val = ret >> 2;
+ if (holdmode) {
+ ret = i2c_smbus_read_word_data(*client,
+ chan->type == IIO_TEMP ?
+ SI7020CMD_TEMP_HOLD :
+ SI7020CMD_RH_HOLD);
+ if (ret < 0)
+ return ret;
+ *val = ret >> 2;
+ } else {
+ ret = i2c_smbus_write_byte(*client,
+ chan->type == IIO_TEMP ?
+ SI7020CMD_TEMP_NO_HOLD :
+ SI7020CMD_RH_NO_HOLD);
+ if (ret < 0)
+ return ret;
+ start = jiffies;
+ while ((ret = i2c_master_recv(*client, buf, 2)) < 0) {
+ if (time_after(jiffies, start +
+ usecs_to_jiffies(
+ chan->type == IIO_TEMP ?
+ SI7020_TEMP_TIMEOUT :
+ SI7020_RH_TIMEOUT)))
+ return ret;
+ usleep_range(SI7020_NOHOLD_SLEEP_MIN,
+ SI7020_NOHOLD_SLEEP_MAX);
+ }
+ *val = ((buf[0] << 8) | buf[1]) >> 2;
+ }
/*
* Humidity values can sligthly exceed the 0-100%RH
* range and should be corrected by software
--
2.5.0
--
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