iio: mlx90614: Implement filter configuration

Implemented Low pass 3db frequency filter which configures
FIR and IIR values within the configuration register of EEPROM.
For more standardized interface we have fixed the FIR value
to 1024, while changes in IIR value are directly connected to
filter responses. The new datasheet version will provide a
simplified table (also in reStructured text format below) with
this change, to provide quick overview of possible settings.

Below sensor timings (bandwidth) are calculated for 3db frequency
low pass filter.

+--------------------+-----------------+
| Filter setting (%) | Band width (Hz) |
|  (rounded to 1.0)  |                 |
+====================+=================+
|         13         |      0.15       |
+--------------------+-----------------+
|         17         |      0.20       |
+--------------------+-----------------+
|         25         |      0.31       |
+--------------------+-----------------+
|         50         |      0.77       |
+--------------------+-----------------+
|         57         |      0.86       |
+--------------------+-----------------+
|         67         |      1.10       |
+--------------------+-----------------+
|         80         |      1.53       |
+--------------------+-----------------+
|        100         |      7.23       |
+--------------------+-----------------+

The diff is made towards togreg branch. Added myself to MAINTAINERS and
authors as per discussion with Jonathan.
Signed-off-by: Crt Mori <cmo@melexis.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

MAINTAINERS

@@ -6757,6 +6757,13 @@ S:	Supported
 F:	include/linux/mlx5/
 F:	drivers/infiniband/hw/mlx5/
 
+MELEXIS MLX90614 DRIVER
+M:	Crt Mori <cmo@melexis.com>
+L:	linux-iio@vger.kernel.org
+W:	http://www.melexis.com
+S:	Supported
+F:	drivers/iio/temperature/mlx90614.c
+
 MN88472 MEDIA DRIVER
 M:	Antti Palosaari <crope@iki.fi>
 L:	linux-media@vger.kernel.org

drivers/iio/temperature/mlx90614.c

@@ -3,6 +3,7 @@
  *
  * Copyright (c) 2014 Peter Meerwald <pmeerw@pmeerw.net>
  * Copyright (c) 2015 Essensium NV
+ * Copyright (c) 2015 Melexis
  *
  * This file is subject to the terms and conditions of version 2 of
  * the GNU General Public License.  See the file COPYING in the main
@@ -20,7 +21,6 @@
  * always has a pull-up so we do not need an extra GPIO to drive it high.  If
  * the "wakeup" GPIO is not given, power management will be disabled.
  *
- * TODO: filter configuration
  */
 
 #include <linux/err.h>
@@ -32,6 +32,7 @@
 #include <linux/pm_runtime.h>
 
 #include <linux/iio/iio.h>
+#include <linux/iio/sysfs.h>
 
 #define MLX90614_OP_RAM		0x00
 #define MLX90614_OP_EEPROM	0x20
@@ -79,6 +80,20 @@ struct mlx90614_data {
 	unsigned long ready_timestamp; /* in jiffies */
 };
 
+/* Bandwidth values for IIR filtering */
+static const int mlx90614_iir_values[] = {77, 31, 20, 15, 723, 153, 110, 86};
+static IIO_CONST_ATTR(in_temp_object_filter_low_pass_3db_frequency_available,
+		      "0.15 0.20 0.31 0.77 0.86 1.10 1.53 7.23");
+
+static struct attribute *mlx90614_attributes[] = {
+	&iio_const_attr_in_temp_object_filter_low_pass_3db_frequency_available.dev_attr.attr,
+	NULL,
+};
+
+static const struct attribute_group mlx90614_attr_group = {
+	.attrs = mlx90614_attributes,
+};
+
 /*
  * Erase an address and write word.
  * The mutex must be locked before calling.
@@ -117,6 +132,42 @@ static s32 mlx90614_write_word(const struct i2c_client *client, u8 command,
 	return ret;
 }
 
+/*
+ * Find the IIR value inside mlx90614_iir_values array and return its position
+ * which is equivalent to the bit value in sensor register
+ */
+static inline s32 mlx90614_iir_search(const struct i2c_client *client,
+				      int value)
+{
+	int i;
+	s32 ret;
+
+	for (i = 0; i < ARRAY_SIZE(mlx90614_iir_values); ++i) {
+		if (value == mlx90614_iir_values[i])
+			break;
+	}
+
+	if (i == ARRAY_SIZE(mlx90614_iir_values))
+		return -EINVAL;
+
+	/*
+	 * CONFIG register values must not be changed so
+	 * we must read them before we actually write
+	 * changes
+	 */
+	ret = i2c_smbus_read_word_data(client, MLX90614_CONFIG);
+	if (ret > 0)
+		return ret;
+
+	/* Write changed values */
+	ret = mlx90614_write_word(client, MLX90614_CONFIG,
+			(i << MLX90614_CONFIG_IIR_SHIFT) |
+			(((u16) ((0x7 << MLX90614_CONFIG_FIR_SHIFT) |
+			((u16) ret & (~((u16) MLX90614_CONFIG_FIR_MASK))))) &
+			(~(u16) MLX90614_CONFIG_IIR_MASK)));
+	return ret;
+}
+
 #ifdef CONFIG_PM
 /*
  * If @startup is true, make sure MLX90614_TIMING_STARTUP ms have elapsed since
@@ -236,6 +287,21 @@ static int mlx90614_read_raw(struct iio_dev *indio_dev,
 			*val2 = ret * MLX90614_CONST_EMISSIVITY_RESOLUTION;
 		}
 		return IIO_VAL_INT_PLUS_NANO;
+	case IIO_CHAN_INFO_LOW_PASS_FILTER_3DB_FREQUENCY: /* IIR setting with
+							     FIR = 1024 */
+		mlx90614_power_get(data, false);
+		mutex_lock(&data->lock);
+		ret = i2c_smbus_read_word_data(data->client, MLX90614_CONFIG);
+		mutex_unlock(&data->lock);
+		mlx90614_power_put(data);
+
+		if (ret < 0)
+			return ret;
+
+		*val = mlx90614_iir_values[ret & MLX90614_CONFIG_IIR_MASK] / 100;
+		*val2 = (mlx90614_iir_values[ret & MLX90614_CONFIG_IIR_MASK] % 100) *
+			10000;
+		return IIO_VAL_INT_PLUS_MICRO;
 	default:
 		return -EINVAL;
 	}
@@ -262,6 +328,18 @@ static int mlx90614_write_raw(struct iio_dev *indio_dev,
 		mutex_unlock(&data->lock);
 		mlx90614_power_put(data);
 
+		return ret;
+	case IIO_CHAN_INFO_LOW_PASS_FILTER_3DB_FREQUENCY: /* IIR Filter setting */
+		if (val < 0 || val2 < 0)
+			return -EINVAL;
+
+		mlx90614_power_get(data, false);
+		mutex_lock(&data->lock);
+		ret = mlx90614_iir_search(data->client,
+					  val * 100 + val2 / 10000);
+		mutex_unlock(&data->lock);
+		mlx90614_power_put(data);
+
 		return ret;
 	default:
 		return -EINVAL;
@@ -275,6 +353,8 @@ static int mlx90614_write_raw_get_fmt(struct iio_dev *indio_dev,
 	switch (mask) {
 	case IIO_CHAN_INFO_CALIBEMISSIVITY:
 		return IIO_VAL_INT_PLUS_NANO;
+	case IIO_CHAN_INFO_LOW_PASS_FILTER_3DB_FREQUENCY:
+		return IIO_VAL_INT_PLUS_MICRO;
 	default:
 		return -EINVAL;
 	}
@@ -294,7 +374,8 @@ static const struct iio_chan_spec mlx90614_channels[] = {
 		.modified = 1,
 		.channel2 = IIO_MOD_TEMP_OBJECT,
 		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
-		    BIT(IIO_CHAN_INFO_CALIBEMISSIVITY),
+		    BIT(IIO_CHAN_INFO_CALIBEMISSIVITY) |
+			BIT(IIO_CHAN_INFO_LOW_PASS_FILTER_3DB_FREQUENCY),
 		.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_OFFSET) |
 		    BIT(IIO_CHAN_INFO_SCALE),
 	},
@@ -305,7 +386,8 @@ static const struct iio_chan_spec mlx90614_channels[] = {
 		.channel = 1,
 		.channel2 = IIO_MOD_TEMP_OBJECT,
 		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
-		    BIT(IIO_CHAN_INFO_CALIBEMISSIVITY),
+		    BIT(IIO_CHAN_INFO_CALIBEMISSIVITY) |
+			BIT(IIO_CHAN_INFO_LOW_PASS_FILTER_3DB_FREQUENCY),
 		.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_OFFSET) |
 		    BIT(IIO_CHAN_INFO_SCALE),
 	},
@@ -315,6 +397,7 @@ static const struct iio_info mlx90614_info = {
 	.read_raw = mlx90614_read_raw,
 	.write_raw = mlx90614_write_raw,
 	.write_raw_get_fmt = mlx90614_write_raw_get_fmt,
+	.attrs = &mlx90614_attr_group,
 	.driver_module = THIS_MODULE,
 };
 
@@ -569,5 +652,6 @@ module_i2c_driver(mlx90614_driver);
 
 MODULE_AUTHOR("Peter Meerwald <pmeerw@pmeerw.net>");
 MODULE_AUTHOR("Vianney le Clément de Saint-Marcq <vianney.leclement@essensium.com>");
+MODULE_AUTHOR("Crt Mori <cmo@melexis.com>");
 MODULE_DESCRIPTION("Melexis MLX90614 contactless IR temperature sensor driver");
 MODULE_LICENSE("GPL");