[PATCH v2 3/3] iio: humidity: si7020: added No Hold read mode

[Nicola Corna <nicola-V0pQiMyom5mh6J55Ss3d3w@public.gmane.org>]

The Si7013/20/21 modules support 2 read modes:
 * Hold mode (blocking), where the device stretches the clock until the end
of the measurement
 * No Hold mode (non-blocking), where the device replies NACK for every I2C
call during the measurement
Here the No Hold mode is implemented, selectable with the blocking_io
variable within si7020_platform_data. The default mode is Hold, unless the
adapter does not support clock stretching, in which case the No Hold mode
is used.

Signed-off-by: Nicola Corna <nicola-V0pQiMyom5mh6J55Ss3d3w@public.gmane.org>
---
This patch depends on patch "[PATCH v4 1/2] iio: humidity: si7020: replaced
bitmask on humidity values with range check"
 drivers/iio/humidity/si7020.c        | 76 ++++++++++++++++++++++++++++++++----
 include/linux/platform_data/si7020.h | 21 ++++++++++
 2 files changed, 90 insertions(+), 7 deletions(-)
 create mode 100644 include/linux/platform_data/si7020.h

diff --git a/drivers/iio/humidity/si7020.c b/drivers/iio/humidity/si7020.c
index 12128d1..9cf9527 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-2SNLKkHU5xRBDgjK7y7TUQ@public.gmane.org>
+ * Copyright (c) 2015 Nicola Corna <nicola-V0pQiMyom5mh6J55Ss3d3w@public.gmane.org>
  *
  * This program is free software; you can redistribute it and/or modify it
  * under the terms and conditions of the GNU General Public License,
@@ -30,33 +31,78 @@
 #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>
+#include <linux/platform_data/si7020.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 int si7020_read_raw(struct iio_dev *indio_dev,
 			   struct iio_chan_spec const *chan, int *val,
 			   int *val2, long mask)
 {
 	struct i2c_client **client = iio_priv(indio_dev);
+	struct si7020_platform_data *pdata;
 	int ret;
+	bool holdmode;
+	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;
+		pdata = dev_get_platdata(&(*client)->dev);
+		if (pdata)
+			holdmode = pdata->blocking_io;
+		else
+			holdmode = !i2c_check_functionality((*client)->adapter,
+						I2C_FUNC_NO_CLK_STRETCH);
+		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 slightly exceed the 0-100%RH
 		 * range and should be corrected by software
@@ -116,6 +162,7 @@ static int si7020_probe(struct i2c_client *client,
 {
 	struct iio_dev *indio_dev;
 	struct i2c_client **data;
+	struct si7020_platform_data *pdata;
 	int ret;
 
 	if (!i2c_check_functionality(client->adapter,
@@ -123,6 +170,21 @@ static int si7020_probe(struct i2c_client *client,
 				     I2C_FUNC_SMBUS_READ_WORD_DATA))
 		return -ENODEV;
 
+	pdata = dev_get_platdata(&client->dev);
+	if (pdata) {
+		if (pdata->blocking_io) {
+			if (i2c_check_functionality(client->adapter,
+						    I2C_FUNC_NO_CLK_STRETCH))
+				return -ENODEV;
+		} else if (!i2c_check_functionality(client->adapter,
+								I2C_FUNC_I2C))
+			return -ENODEV;
+	} else
+		if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C) &&
+		   i2c_check_functionality(client->adapter,
+					   I2C_FUNC_NO_CLK_STRETCH))
+			return -ENODEV;
+
 	/* Reset device, loads default settings. */
 	ret = i2c_smbus_write_byte(client, SI7020CMD_RESET);
 	if (ret < 0)
diff --git a/include/linux/platform_data/si7020.h b/include/linux/platform_data/si7020.h
new file mode 100644
index 0000000..8bb5848
--- /dev/null
+++ b/include/linux/platform_data/si7020.h
@@ -0,0 +1,21 @@
+/*
+ * Copyright (C) 2015 Nicola Corna <nicola-V0pQiMyom5mh6J55Ss3d3w@public.gmane.org>
+ *
+ * This software is licensed under the terms of the GNU General Public
+ * License version 2, as published by the Free Software Foundation, and
+ * may be copied, distributed, and modified under those terms.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ */
+
+#ifndef __SI7020_H_
+#define __SI7020_H_
+
+struct si7020_platform_data {
+	bool blocking_io;
+};
+#endif /* __SI7020_H_ */
-- 
2.5.1