iio:pressure:ms5611: oversampling rate support

Add support for setting and retrieving OverSampling Rate independently for
each of the temperature and pressure channels. This allows userspace to
fine tune hardware sampling process according to the following tradeoffs :
* the higher the OSR, the finer the resolution ;
* the higher the OSR, the lower the noise ;
BUT:
* the higher the OSR, the larger the drift ;
* the higher the OSR, the longer the response time, i.e. less samples per
  unit of time.

Signed-off-by: Gregor Boirie <gregor.boirie@parrot.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/pressure/ms5611.h

@@ -19,12 +19,6 @@
 #define MS5611_RESET			0x1e
 #define MS5611_READ_ADC			0x00
 #define MS5611_READ_PROM_WORD		0xA0
-#define MS5611_START_TEMP_CONV		0x58
-#define MS5611_START_PRESSURE_CONV	0x48
-
-#define MS5611_CONV_TIME_MIN		9040
-#define MS5611_CONV_TIME_MAX		10000
-
 #define MS5611_PROM_WORDS_NB		8
 
 enum {
@@ -39,10 +33,24 @@ struct ms5611_chip_info {
 					    s32 *temp, s32 *pressure);
 };
 
+/*
+ * OverSampling Rate descriptor.
+ * Warning: cmd MUST be kept aligned on a word boundary (see
+ * m5611_spi_read_adc_temp_and_pressure in ms5611_spi.c).
+ */
+struct ms5611_osr {
+	unsigned long conv_usec;
+	u8 cmd;
+	unsigned short rate;
+};
+
 struct ms5611_state {
 	void *client;
 	struct mutex lock;
 
+	const struct ms5611_osr *pressure_osr;
+	const struct ms5611_osr *temp_osr;
+
 	int (*reset)(struct device *dev);
 	int (*read_prom_word)(struct device *dev, int index, u16 *word);
 	int (*read_adc_temp_and_pressure)(struct device *dev,

drivers/iio/pressure/ms5611_core.c

@@ -18,11 +18,44 @@
 #include <linux/delay.h>
 #include <linux/regulator/consumer.h>
 
+#include <linux/iio/sysfs.h>
 #include <linux/iio/buffer.h>
 #include <linux/iio/triggered_buffer.h>
 #include <linux/iio/trigger_consumer.h>
 #include "ms5611.h"
 
+#define MS5611_INIT_OSR(_cmd, _conv_usec, _rate) \
+	{ .cmd = _cmd, .conv_usec = _conv_usec, .rate = _rate }
+
+static const struct ms5611_osr ms5611_avail_pressure_osr[] = {
+	MS5611_INIT_OSR(0x40, 600,  256),
+	MS5611_INIT_OSR(0x42, 1170, 512),
+	MS5611_INIT_OSR(0x44, 2280, 1024),
+	MS5611_INIT_OSR(0x46, 4540, 2048),
+	MS5611_INIT_OSR(0x48, 9040, 4096)
+};
+
+static const struct ms5611_osr ms5611_avail_temp_osr[] = {
+	MS5611_INIT_OSR(0x50, 600,  256),
+	MS5611_INIT_OSR(0x52, 1170, 512),
+	MS5611_INIT_OSR(0x54, 2280, 1024),
+	MS5611_INIT_OSR(0x56, 4540, 2048),
+	MS5611_INIT_OSR(0x58, 9040, 4096)
+};
+
+static const char ms5611_show_osr[] = "256 512 1024 2048 4096";
+
+static IIO_CONST_ATTR(oversampling_ratio_available, ms5611_show_osr);
+
+static struct attribute *ms5611_attributes[] = {
+	&iio_const_attr_oversampling_ratio_available.dev_attr.attr,
+	NULL,
+};
+
+static const struct attribute_group ms5611_attribute_group = {
+	.attrs = ms5611_attributes,
+};
+
 static bool ms5611_prom_is_valid(u16 *prom, size_t len)
 {
 	int i, j;
@@ -239,11 +272,70 @@ static int ms5611_read_raw(struct iio_dev *indio_dev,
 		default:
 			return -EINVAL;
 		}
+	case IIO_CHAN_INFO_OVERSAMPLING_RATIO:
+		if (chan->type != IIO_TEMP && chan->type != IIO_PRESSURE)
+			break;
+		mutex_lock(&st->lock);
+		if (chan->type == IIO_TEMP)
+			*val = (int)st->temp_osr->rate;
+		else
+			*val = (int)st->pressure_osr->rate;
+		mutex_unlock(&st->lock);
+		return IIO_VAL_INT;
 	}
 
 	return -EINVAL;
 }
 
+static const struct ms5611_osr *ms5611_find_osr(int rate,
+						const struct ms5611_osr *osr,
+						size_t count)
+{
+	unsigned int r;
+
+	for (r = 0; r < count; r++)
+		if ((unsigned short)rate == osr[r].rate)
+			break;
+	if (r >= count)
+		return NULL;
+	return &osr[r];
+}
+
+static int ms5611_write_raw(struct iio_dev *indio_dev,
+			    struct iio_chan_spec const *chan,
+			    int val, int val2, long mask)
+{
+	struct ms5611_state *st = iio_priv(indio_dev);
+	const struct ms5611_osr *osr = NULL;
+
+	if (mask != IIO_CHAN_INFO_OVERSAMPLING_RATIO)
+		return -EINVAL;
+
+	if (chan->type == IIO_TEMP)
+		osr = ms5611_find_osr(val, ms5611_avail_temp_osr,
+				      ARRAY_SIZE(ms5611_avail_temp_osr));
+	else if (chan->type == IIO_PRESSURE)
+		osr = ms5611_find_osr(val, ms5611_avail_pressure_osr,
+				      ARRAY_SIZE(ms5611_avail_pressure_osr));
+	if (!osr)
+		return -EINVAL;
+
+	mutex_lock(&st->lock);
+
+	if (iio_buffer_enabled(indio_dev)) {
+		mutex_unlock(&st->lock);
+		return -EBUSY;
+	}
+
+	if (chan->type == IIO_TEMP)
+		st->temp_osr = osr;
+	else
+		st->pressure_osr = osr;
+
+	mutex_unlock(&st->lock);
+	return 0;
+}
+
 static const unsigned long ms5611_scan_masks[] = {0x3, 0};
 
 static struct ms5611_chip_info chip_info_tbl[] = {
@@ -259,7 +351,8 @@ static const struct iio_chan_spec ms5611_channels[] = {
 	{
 		.type = IIO_PRESSURE,
 		.info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED) |
-			BIT(IIO_CHAN_INFO_SCALE),
+			BIT(IIO_CHAN_INFO_SCALE) |
+			BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO),
 		.scan_index = 0,
 		.scan_type = {
 			.sign = 's',
@@ -271,7 +364,8 @@ static const struct iio_chan_spec ms5611_channels[] = {
 	{
 		.type = IIO_TEMP,
 		.info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED) |
-			BIT(IIO_CHAN_INFO_SCALE),
+			BIT(IIO_CHAN_INFO_SCALE) |
+			BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO),
 		.scan_index = 1,
 		.scan_type = {
 			.sign = 's',
@@ -285,6 +379,8 @@ static const struct iio_chan_spec ms5611_channels[] = {
 
 static const struct iio_info ms5611_info = {
 	.read_raw = &ms5611_read_raw,
+	.write_raw = &ms5611_write_raw,
+	.attrs = &ms5611_attribute_group,
 	.driver_module = THIS_MODULE,
 };
 
@@ -319,6 +415,11 @@ int ms5611_probe(struct iio_dev *indio_dev, struct device *dev,
 
 	mutex_init(&st->lock);
 	st->chip_info = &chip_info_tbl[type];
+	st->temp_osr =
+		&ms5611_avail_temp_osr[ARRAY_SIZE(ms5611_avail_temp_osr) - 1];
+	st->pressure_osr =
+		&ms5611_avail_pressure_osr[ARRAY_SIZE(ms5611_avail_pressure_osr)
+					   - 1];
 	indio_dev->dev.parent = dev;
 	indio_dev->name = name;
 	indio_dev->info = &ms5611_info;

drivers/iio/pressure/ms5611_i2c.c

@@ -63,23 +63,23 @@ static int ms5611_i2c_read_adc_temp_and_pressure(struct device *dev,
 {
 	int ret;
 	struct ms5611_state *st = iio_priv(dev_to_iio_dev(dev));
+	const struct ms5611_osr *osr = st->temp_osr;
 
-	ret = i2c_smbus_write_byte(st->client, MS5611_START_TEMP_CONV);
+	ret = i2c_smbus_write_byte(st->client, osr->cmd);
 	if (ret < 0)
 		return ret;
 
-	usleep_range(MS5611_CONV_TIME_MIN, MS5611_CONV_TIME_MAX);
-
+	usleep_range(osr->conv_usec, osr->conv_usec + (osr->conv_usec / 10UL));
 	ret = ms5611_i2c_read_adc(st, temp);
 	if (ret < 0)
 		return ret;
 
-	ret = i2c_smbus_write_byte(st->client, MS5611_START_PRESSURE_CONV);
+	osr = st->pressure_osr;
+	ret = i2c_smbus_write_byte(st->client, osr->cmd);
 	if (ret < 0)
 		return ret;
 
-	usleep_range(MS5611_CONV_TIME_MIN, MS5611_CONV_TIME_MAX);
-
+	usleep_range(osr->conv_usec, osr->conv_usec + (osr->conv_usec / 10UL));
 	return ms5611_i2c_read_adc(st, pressure);
 }
 

drivers/iio/pressure/ms5611_spi.c

@@ -56,28 +56,29 @@ static int ms5611_spi_read_adc(struct device *dev, s32 *val)
 static int ms5611_spi_read_adc_temp_and_pressure(struct device *dev,
 						 s32 *temp, s32 *pressure)
 {
-	u8 cmd;
 	int ret;
 	struct ms5611_state *st = iio_priv(dev_to_iio_dev(dev));
+	const struct ms5611_osr *osr = st->temp_osr;
 
-	cmd = MS5611_START_TEMP_CONV;
-	ret = spi_write_then_read(st->client, &cmd, 1, NULL, 0);
+	/*
+	 * Warning: &osr->cmd MUST be aligned on a word boundary since used as
+	 * 2nd argument (void*) of spi_write_then_read.
+	 */
+	ret = spi_write_then_read(st->client, &osr->cmd, 1, NULL, 0);
 	if (ret < 0)
 		return ret;
 
-	usleep_range(MS5611_CONV_TIME_MIN, MS5611_CONV_TIME_MAX);
-
+	usleep_range(osr->conv_usec, osr->conv_usec + (osr->conv_usec / 10UL));
 	ret = ms5611_spi_read_adc(dev, temp);
 	if (ret < 0)
 		return ret;
 
-	cmd = MS5611_START_PRESSURE_CONV;
-	ret = spi_write_then_read(st->client, &cmd, 1, NULL, 0);
+	osr = st->pressure_osr;
+	ret = spi_write_then_read(st->client, &osr->cmd, 1, NULL, 0);
 	if (ret < 0)
 		return ret;
 
-	usleep_range(MS5611_CONV_TIME_MIN, MS5611_CONV_TIME_MAX);
-
+	usleep_range(osr->conv_usec, osr->conv_usec + (osr->conv_usec / 10UL));
 	return ms5611_spi_read_adc(dev, pressure);
 }