iio: mma8452: add support for oversampling ratio

This adds the following sysfs files according to the iio ABI:

-rw-r--r--    4096 in_accel_oversampling_ratio
-r--r--r--    4096 in_accel_oversampling_ratio_available

Internally, the device knows about 4 different power modes that differ
in oversampling ratio (and power consumption). We just show the user
what oversampling ratio(s) is/are available, depending on the current
frequency.

The referenced table in the datasheets makes it easier to understand.

Signed-off-by: Martin Kepplinger <martink@posteo.de>
Signed-off-by: Christoph Muellner <christoph.muellner@theobroma-systems.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/accel/mma8452.c

@@ -76,6 +76,8 @@
 #define  MMA8452_CTRL_DR_DEFAULT		0x4 /* 50 Hz sample frequency */
 #define MMA8452_CTRL_REG2			0x2b
 #define  MMA8452_CTRL_REG2_RST			BIT(6)
+#define  MMA8452_CTRL_REG2_MODS_SHIFT		3
+#define  MMA8452_CTRL_REG2_MODS_MASK		0x1b
 #define MMA8452_CTRL_REG4			0x2d
 #define MMA8452_CTRL_REG5			0x2e
 #define MMA8452_OFF_X				0x2f
@@ -257,20 +259,17 @@ static const int mma8452_samp_freq[8][2] = {
 	{6, 250000}, {1, 560000}
 };
 
-/* Datasheet table 35  (step time vs sample frequency) */
-static const int mma8452_transient_time_step_us[8] = {
-	1250,
-	2500,
-	5000,
-	10000,
-	20000,
-	20000,
-	20000,
-	20000
+/* Datasheet table: step time "Relationship with the ODR" (sample frequency) */
+static const int mma8452_transient_time_step_us[4][8] = {
+	{ 1250, 2500, 5000, 10000, 20000, 20000, 20000, 20000 },  /* normal */
+	{ 1250, 2500, 5000, 10000, 20000, 80000, 80000, 80000 },  /* l p l n */
+	{ 1250, 2500, 2500, 2500, 2500, 2500, 2500, 2500 },	  /* high res*/
+	{ 1250, 2500, 5000, 10000, 20000, 80000, 160000, 160000 } /* l p */
 };
 
-/* Datasheet table 18 (normal mode) */
-static const int mma8452_hp_filter_cutoff[8][4][2] = {
+/* Datasheet table "High-Pass Filter Cutoff Options" */
+static const int mma8452_hp_filter_cutoff[4][8][4][2] = {
+	{ /* normal */
 	{ {16, 0}, {8, 0}, {4, 0}, {2, 0} },		/* 800 Hz sample */
 	{ {16, 0}, {8, 0}, {4, 0}, {2, 0} },		/* 400 Hz sample */
 	{ {8, 0}, {4, 0}, {2, 0}, {1, 0} },		/* 200 Hz sample */
@@ -279,8 +278,61 @@ static const int mma8452_hp_filter_cutoff[8][4][2] = {
 	{ {2, 0}, {1, 0}, {0, 500000}, {0, 250000} },	/* 12.5 Hz sample */
 	{ {2, 0}, {1, 0}, {0, 500000}, {0, 250000} },	/* 6.25 Hz sample */
 	{ {2, 0}, {1, 0}, {0, 500000}, {0, 250000} }	/* 1.56 Hz sample */
+	},
+	{ /* low noise low power */
+	{ {16, 0}, {8, 0}, {4, 0}, {2, 0} },
+	{ {16, 0}, {8, 0}, {4, 0}, {2, 0} },
+	{ {8, 0}, {4, 0}, {2, 0}, {1, 0} },
+	{ {4, 0}, {2, 0}, {1, 0}, {0, 500000} },
+	{ {2, 0}, {1, 0}, {0, 500000}, {0, 250000} },
+	{ {0, 500000}, {0, 250000}, {0, 125000}, {0, 063000} },
+	{ {0, 500000}, {0, 250000}, {0, 125000}, {0, 063000} },
+	{ {0, 500000}, {0, 250000}, {0, 125000}, {0, 063000} }
+	},
+	{ /* high resolution */
+	{ {16, 0}, {8, 0}, {4, 0}, {2, 0} },
+	{ {16, 0}, {8, 0}, {4, 0}, {2, 0} },
+	{ {16, 0}, {8, 0}, {4, 0}, {2, 0} },
+	{ {16, 0}, {8, 0}, {4, 0}, {2, 0} },
+	{ {16, 0}, {8, 0}, {4, 0}, {2, 0} },
+	{ {16, 0}, {8, 0}, {4, 0}, {2, 0} },
+	{ {16, 0}, {8, 0}, {4, 0}, {2, 0} },
+	{ {16, 0}, {8, 0}, {4, 0}, {2, 0} }
+	},
+	{ /* low power */
+	{ {16, 0}, {8, 0}, {4, 0}, {2, 0} },
+	{ {8, 0}, {4, 0}, {2, 0}, {1, 0} },
+	{ {4, 0}, {2, 0}, {1, 0}, {0, 500000} },
+	{ {2, 0}, {1, 0}, {0, 500000}, {0, 250000} },
+	{ {1, 0}, {0, 500000}, {0, 250000}, {0, 125000} },
+	{ {0, 250000}, {0, 125000}, {0, 063000}, {0, 031000} },
+	{ {0, 250000}, {0, 125000}, {0, 063000}, {0, 031000} },
+	{ {0, 250000}, {0, 125000}, {0, 063000}, {0, 031000} }
+	}
 };
 
+/* Datasheet table "MODS Oversampling modes averaging values at each ODR" */
+static const u16 mma8452_os_ratio[4][8] = {
+	/* 800 Hz, 400 Hz, ... , 1.56 Hz */
+	{ 2, 4, 4, 4, 4, 16, 32, 128 },		/* normal */
+	{ 2, 4, 4, 4, 4, 4, 8, 32 },		/* low power low noise */
+	{ 2, 4, 8, 16, 32, 128, 256, 1024 },	/* high resolution */
+	{ 2, 2, 2, 2, 2, 2, 4, 16 }		/* low power */
+};
+
+static int mma8452_get_power_mode(struct mma8452_data *data)
+{
+	int reg;
+
+	reg = i2c_smbus_read_byte_data(data->client,
+				       MMA8452_CTRL_REG2);
+	if (reg < 0)
+		return reg;
+
+	return ((reg & MMA8452_CTRL_REG2_MODS_MASK) >>
+		MMA8452_CTRL_REG2_MODS_SHIFT);
+}
+
 static ssize_t mma8452_show_samp_freq_avail(struct device *dev,
 					    struct device_attribute *attr,
 					    char *buf)
@@ -303,13 +355,42 @@ static ssize_t mma8452_show_scale_avail(struct device *dev,
 static ssize_t mma8452_show_hp_cutoff_avail(struct device *dev,
 					    struct device_attribute *attr,
 					    char *buf)
+{
+	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
+	struct mma8452_data *data = iio_priv(indio_dev);
+	int i, j;
+
+	i = mma8452_get_odr_index(data);
+	j = mma8452_get_power_mode(data);
+	if (j < 0)
+		return j;
+
+	return mma8452_show_int_plus_micros(buf, mma8452_hp_filter_cutoff[j][i],
+		ARRAY_SIZE(mma8452_hp_filter_cutoff[0][0]));
+}
+
+static ssize_t mma8452_show_os_ratio_avail(struct device *dev,
+					   struct device_attribute *attr,
+					   char *buf)
 {
 	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
 	struct mma8452_data *data = iio_priv(indio_dev);
 	int i = mma8452_get_odr_index(data);
+	int j;
+	u16 val = 0;
+	size_t len = 0;
+
+	for (j = 0; j < ARRAY_SIZE(mma8452_os_ratio); j++) {
+		if (val == mma8452_os_ratio[j][i])
+			continue;
+
+		val = mma8452_os_ratio[j][i];
+
+		len += scnprintf(buf + len, PAGE_SIZE - len, "%d ", val);
+	}
+	buf[len - 1] = '\n';
 
-	return mma8452_show_int_plus_micros(buf, mma8452_hp_filter_cutoff[i],
-		ARRAY_SIZE(mma8452_hp_filter_cutoff[0]));
+	return len;
 }
 
 static IIO_DEV_ATTR_SAMP_FREQ_AVAIL(mma8452_show_samp_freq_avail);
@@ -317,6 +398,8 @@ static IIO_DEVICE_ATTR(in_accel_scale_available, S_IRUGO,
 		       mma8452_show_scale_avail, NULL, 0);
 static IIO_DEVICE_ATTR(in_accel_filter_high_pass_3db_frequency_available,
 		       S_IRUGO, mma8452_show_hp_cutoff_avail, NULL, 0);
+static IIO_DEVICE_ATTR(in_accel_oversampling_ratio_available, S_IRUGO,
+		       mma8452_show_os_ratio_avail, NULL, 0);
 
 static int mma8452_get_samp_freq_index(struct mma8452_data *data,
 				       int val, int val2)
@@ -335,24 +418,33 @@ static int mma8452_get_scale_index(struct mma8452_data *data, int val, int val2)
 static int mma8452_get_hp_filter_index(struct mma8452_data *data,
 				       int val, int val2)
 {
-	int i = mma8452_get_odr_index(data);
+	int i, j;
+
+	i = mma8452_get_odr_index(data);
+	j = mma8452_get_power_mode(data);
+	if (j < 0)
+		return j;
 
-	return mma8452_get_int_plus_micros_index(mma8452_hp_filter_cutoff[i],
-		ARRAY_SIZE(mma8452_hp_filter_cutoff[0]), val, val2);
+	return mma8452_get_int_plus_micros_index(mma8452_hp_filter_cutoff[j][i],
+		ARRAY_SIZE(mma8452_hp_filter_cutoff[0][0]), val, val2);
 }
 
 static int mma8452_read_hp_filter(struct mma8452_data *data, int *hz, int *uHz)
 {
-	int i, ret;
+	int j, i, ret;
 
 	ret = i2c_smbus_read_byte_data(data->client, MMA8452_HP_FILTER_CUTOFF);
 	if (ret < 0)
 		return ret;
 
 	i = mma8452_get_odr_index(data);
+	j = mma8452_get_power_mode(data);
+	if (j < 0)
+		return j;
+
 	ret &= MMA8452_HP_FILTER_CUTOFF_SEL_MASK;
-	*hz = mma8452_hp_filter_cutoff[i][ret][0];
-	*uHz = mma8452_hp_filter_cutoff[i][ret][1];
+	*hz = mma8452_hp_filter_cutoff[j][i][ret][0];
+	*uHz = mma8452_hp_filter_cutoff[j][i][ret][1];
 
 	return 0;
 }
@@ -414,6 +506,15 @@ static int mma8452_read_raw(struct iio_dev *indio_dev,
 		}
 
 		return IIO_VAL_INT_PLUS_MICRO;
+	case IIO_CHAN_INFO_OVERSAMPLING_RATIO:
+		ret = mma8452_get_power_mode(data);
+		if (ret < 0)
+			return ret;
+
+		i = mma8452_get_odr_index(data);
+
+		*val = mma8452_os_ratio[ret][i];
+		return IIO_VAL_INT;
 	}
 
 	return -EINVAL;
@@ -480,6 +581,21 @@ fail:
 	return ret;
 }
 
+static int mma8452_set_power_mode(struct mma8452_data *data, u8 mode)
+{
+	int reg;
+
+	reg = i2c_smbus_read_byte_data(data->client,
+				       MMA8452_CTRL_REG2);
+	if (reg < 0)
+		return reg;
+
+	reg &= ~MMA8452_CTRL_REG2_MODS_MASK;
+	reg |= mode << MMA8452_CTRL_REG2_MODS_SHIFT;
+
+	return mma8452_change_config(data, MMA8452_CTRL_REG2, reg);
+}
+
 /* returns >0 if in freefall mode, 0 if not or <0 if an error occurred */
 static int mma8452_freefall_mode_enabled(struct mma8452_data *data)
 {
@@ -597,6 +713,14 @@ static int mma8452_write_raw(struct iio_dev *indio_dev,
 		return mma8452_change_config(data, MMA8452_DATA_CFG,
 					     data->data_cfg);
 
+	case IIO_CHAN_INFO_OVERSAMPLING_RATIO:
+		ret = mma8452_get_odr_index(data);
+
+		for (i = 0; i < ARRAY_SIZE(mma8452_os_ratio); i++) {
+			if (mma8452_os_ratio[i][ret] == val)
+				return mma8452_set_power_mode(data, i);
+		}
+
 	default:
 		return -EINVAL;
 	}
@@ -610,7 +734,7 @@ static int mma8452_read_thresh(struct iio_dev *indio_dev,
 			       int *val, int *val2)
 {
 	struct mma8452_data *data = iio_priv(indio_dev);
-	int ret, us;
+	int ret, us, power_mode;
 
 	switch (info) {
 	case IIO_EV_INFO_VALUE:
@@ -629,7 +753,11 @@ static int mma8452_read_thresh(struct iio_dev *indio_dev,
 		if (ret < 0)
 			return ret;
 
-		us = ret * mma8452_transient_time_step_us[
+		power_mode = mma8452_get_power_mode(data);
+		if (power_mode < 0)
+			return power_mode;
+
+		us = ret * mma8452_transient_time_step_us[power_mode][
 				mma8452_get_odr_index(data)];
 		*val = us / USEC_PER_SEC;
 		*val2 = us % USEC_PER_SEC;
@@ -677,8 +805,12 @@ static int mma8452_write_thresh(struct iio_dev *indio_dev,
 					     val);
 
 	case IIO_EV_INFO_PERIOD:
+		ret = mma8452_get_power_mode(data);
+		if (ret < 0)
+			return ret;
+
 		steps = (val * USEC_PER_SEC + val2) /
-				mma8452_transient_time_step_us[
+				mma8452_transient_time_step_us[ret][
 					mma8452_get_odr_index(data)];
 
 		if (steps < 0 || steps > 0xff)
@@ -978,7 +1110,8 @@ static struct attribute_group mma8452_event_attribute_group = {
 			      BIT(IIO_CHAN_INFO_CALIBBIAS), \
 	.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SAMP_FREQ) | \
 			BIT(IIO_CHAN_INFO_SCALE) | \
-			BIT(IIO_CHAN_INFO_HIGH_PASS_FILTER_3DB_FREQUENCY), \
+			BIT(IIO_CHAN_INFO_HIGH_PASS_FILTER_3DB_FREQUENCY) | \
+			BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO), \
 	.scan_index = idx, \
 	.scan_type = { \
 		.sign = 's', \
@@ -998,7 +1131,8 @@ static struct attribute_group mma8452_event_attribute_group = {
 	.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) | \
 		BIT(IIO_CHAN_INFO_CALIBBIAS), \
 	.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SAMP_FREQ) | \
-		BIT(IIO_CHAN_INFO_SCALE), \
+		BIT(IIO_CHAN_INFO_SCALE) | \
+		BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO), \
 	.scan_index = idx, \
 	.scan_type = { \
 		.sign = 's', \
@@ -1171,6 +1305,7 @@ static struct attribute *mma8452_attributes[] = {
 	&iio_dev_attr_sampling_frequency_available.dev_attr.attr,
 	&iio_dev_attr_in_accel_scale_available.dev_attr.attr,
 	&iio_dev_attr_in_accel_filter_high_pass_3db_frequency_available.dev_attr.attr,
+	&iio_dev_attr_in_accel_oversampling_ratio_available.dev_attr.attr,
 	NULL
 };