Re: [PATCH 6/6] iio: mcp9600: Add support for IIR filter

[David Lechner <dlechner@baylibre.com>]

On 8/18/25 1:32 PM, Ben Collins wrote:
> From: Ben Collins <bcollins@watter.com>
> 
> MCP9600 supports an IIR filter with 7 levels. Add IIR attribute
> to allow get/set of this value.
> 
> Use a filter_type[none, ema] for enabling the IIR filter.
> 
> Signed-off-by: Ben Collins <bcollins@watter.com>
> ---
>  drivers/iio/temperature/mcp9600.c | 157 ++++++++++++++++++++++++++++++
>  1 file changed, 157 insertions(+)
> 
> diff --git a/drivers/iio/temperature/mcp9600.c b/drivers/iio/temperature/mcp9600.c
> index 9b017820efc1..0ec47cbeb88c 100644
> --- a/drivers/iio/temperature/mcp9600.c
> +++ b/drivers/iio/temperature/mcp9600.c
> @@ -31,6 +31,7 @@
>  #define MCP9600_STATUS_ALERT(x)		BIT(x)
>  #define MCP9600_SENSOR_CFG		0x05
>  #define MCP9600_SENSOR_TYPE_MASK	GENMASK(6, 4)
> +#define MCP9600_FILTER_MASK		GENMASK(2, 0)
>  #define MCP9600_ALERT_CFG1		0x08
>  #define MCP9600_ALERT_CFG(x)		(MCP9600_ALERT_CFG1 + (x - 1))
>  #define MCP9600_ALERT_CFG_ENABLE	BIT(0)
> @@ -94,6 +95,27 @@ static const int mcp9600_tc_types[] = {
>  	[THERMOCOUPLE_TYPE_R] = 'R',
>  };
>  
> +enum mcp9600_filter {
> +	MCP9600_FILTER_TYPE_NONE,
> +	MCP9600_FILTER_TYPE_EMA,
> +};
> +
> +static const char * const mcp9600_filter_type[] = {
> +	[MCP9600_FILTER_TYPE_NONE] = "none",
> +	[MCP9600_FILTER_TYPE_EMA] = "ema",
> +};
> +
> +static const int mcp_iir_coefficients_avail[7][2] = {
> +	/* Level 0 is no filter */
> +	{ 0, 524549 },
> +	{ 0, 243901 },
> +	{ 0, 119994 },
> +	{ 0,  59761 },
> +	{ 0,  29851 },
> +	{ 0,  14922 },
> +	{ 0,   7461 },
> +};
> +
>  static const struct iio_event_spec mcp9600_events[] = {
>  	{
>  		.type = IIO_EV_TYPE_THRESH,
> @@ -118,7 +140,11 @@ static const struct iio_event_spec mcp9600_events[] = {
>  			.address = MCP9600_HOT_JUNCTION,		       \
>  			.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |	       \
>  					      BIT(IIO_CHAN_INFO_THERMOCOUPLE_TYPE) | \
> +					      BIT(IIO_CHAN_INFO_LOW_PASS_FILTER_3DB_FREQUENCY) |  \
>  					      BIT(IIO_CHAN_INFO_SCALE),	       \
> +			.info_mask_separate_available =                        \
> +					      BIT(IIO_CHAN_INFO_LOW_PASS_FILTER_3DB_FREQUENCY), \
> +			.ext_info = mcp9600_ext_filter,			       \
>  			.event_spec = &mcp9600_events[hj_ev_spec_off],	       \
>  			.num_event_specs = hj_num_ev,			       \
>  		},							       \
> @@ -134,6 +160,26 @@ static const struct iio_event_spec mcp9600_events[] = {
>  		},							       \
>  	}
>  
> +static int mcp9600_get_filter(struct iio_dev *indio_dev,
> +			      struct iio_chan_spec const *chan);
> +static int mcp9600_set_filter(struct iio_dev *indio_dev,
> +			      struct iio_chan_spec const *chan,
> +			      unsigned int mode);
> +
> +static const struct iio_enum mcp9600_filter_enum = {
> +	.items = mcp9600_filter_type,
> +	.num_items = ARRAY_SIZE(mcp9600_filter_type),
> +	.get = mcp9600_get_filter,
> +	.set = mcp9600_set_filter,
> +};
> +
> +static const struct iio_chan_spec_ext_info mcp9600_ext_filter[] = {
> +	IIO_ENUM("filter_type", IIO_SHARED_BY_ALL, &mcp9600_filter_enum),
> +	IIO_ENUM_AVAILABLE("filter_type", IIO_SHARED_BY_ALL,
> +			   &mcp9600_filter_enum),
> +	{ }
> +};
> +
>  static const struct iio_chan_spec mcp9600_channels[][2] = {
>  	MCP9600_CHANNELS(0, 0, 0, 0), /* Alerts: - - - - */
>  	MCP9600_CHANNELS(1, 0, 0, 0), /* Alerts: 1 - - - */
> @@ -161,6 +207,8 @@ struct mcp_chip_info {
>  struct mcp9600_data {
>  	struct i2c_client *client;
>  	u32 thermocouple_type;
> +	/* Filter enabled is 1-7, with 0 being off (filter_type none) */
> +	u8 filter_level;
>  };
>  
>  static int mcp9600_read(struct mcp9600_data *data,
> @@ -191,13 +239,45 @@ static int mcp9600_read_raw(struct iio_dev *indio_dev,
>  		if (ret)
>  			return ret;
>  		return IIO_VAL_INT;
> +
>  	case IIO_CHAN_INFO_SCALE:
>  		*val = 62;
>  		*val2 = 500000;
>  		return IIO_VAL_INT_PLUS_MICRO;
> +
>  	case IIO_CHAN_INFO_THERMOCOUPLE_TYPE:
>  		*val = mcp9600_tc_types[data->thermocouple_type];
>  		return IIO_VAL_CHAR;
> +
> +	case IIO_CHAN_INFO_LOW_PASS_FILTER_3DB_FREQUENCY:
> +		if (data->filter_level == 0)
> +			return -EINVAL;

To implement Jonathan's request from v5, drop this error return.
We'll also need a separate bool data->is_filter_enabled field so
that we can keep the last set filter_level even when the filter
is disabled. (i.e. data->filter_level is never == 0).

This way, if you set the filter level, you can enable and disable
the filter via filter_type and still have the same filter level.

> +
> +		*val = mcp_iir_coefficients_avail[data->filter_level - 1][0];
> +		*val2 = mcp_iir_coefficients_avail[data->filter_level - 1][1];
> +		return IIO_VAL_INT_PLUS_MICRO;
> +
> +	default:
> +		return -EINVAL;
> +	}
> +}
> +
> +static int mcp9600_read_avail(struct iio_dev *indio_dev,
> +			      struct iio_chan_spec const *chan,
> +			      const int **vals, int *type, int *length,
> +			      long mask)
> +{
> +	struct mcp9600_data *data = iio_priv(indio_dev);
> +
> +	switch (mask) {
> +	case IIO_CHAN_INFO_LOW_PASS_FILTER_3DB_FREQUENCY:
> +		if (data->filter_level == 0)
> +			return -EINVAL;
> +
> +		*vals = (int *)mcp_iir_coefficients_avail;
> +		*type = IIO_VAL_INT_PLUS_MICRO;
> +		*length = 2 * ARRAY_SIZE(mcp_iir_coefficients_avail);
> +		return IIO_AVAIL_LIST;
>  	default:
>  		return -EINVAL;
>  	}
> @@ -211,6 +291,7 @@ static int mcp9600_config(struct mcp9600_data *data)
>  
>  	cfg  = FIELD_PREP(MCP9600_SENSOR_TYPE_MASK,
>  			  mcp9600_type_map[data->thermocouple_type]);
> +	FIELD_MODIFY(MCP9600_FILTER_MASK, &cfg, data->filter_level);

And change the logic here to:

	FIELD_MODIFY(MCP9600_FILTER_MASK, &cfg, data->is_filter_enabled ?
		     data->filter_level : 0);

>  
>  	ret = i2c_smbus_write_byte_data(client, MCP9600_SENSOR_CFG, cfg);
>  	if (ret < 0) {
> @@ -221,6 +302,79 @@ static int mcp9600_config(struct mcp9600_data *data)
>  	return 0;
>  }
>  
> +static int mcp9600_write_raw_get_fmt(struct iio_dev *indio_dev,
> +				     struct iio_chan_spec const *chan,
> +				     long mask)
> +{
> +	switch (mask) {
> +	case IIO_CHAN_INFO_LOW_PASS_FILTER_3DB_FREQUENCY:
> +		return IIO_VAL_INT_PLUS_MICRO;
> +	default:
> +		return -EINVAL;
> +	}
> +}
> +
> +static int mcp9600_write_raw(struct iio_dev *indio_dev,
> +			     struct iio_chan_spec const *chan,
> +			     int val, int val2, long mask)
> +{
> +	struct mcp9600_data *data = iio_priv(indio_dev);
> +	int i;
> +
> +	switch (mask) {
> +	case IIO_CHAN_INFO_LOW_PASS_FILTER_3DB_FREQUENCY:
> +		for (i = 0; i < ARRAY_SIZE(mcp_iir_coefficients_avail); i++) {
> +			if (mcp_iir_coefficients_avail[i][0] == val &&
> +			    mcp_iir_coefficients_avail[i][1] == val2)
> +				break;
> +		}
> +
> +		if (i == ARRAY_SIZE(mcp_iir_coefficients_avail))
> +			return -EINVAL;
> +
> +		data->filter_level = i + 1;
> +		return mcp9600_config(data);
> +
> +	default:
> +		return -EINVAL;
> +	}
> +}
> +
> +static int mcp9600_get_filter(struct iio_dev *indio_dev,
> +			      struct iio_chan_spec const *chan)
> +{
> +	struct mcp9600_data *data = iio_priv(indio_dev);
> +
> +	if (data->filter_level == 0)
> +		return MCP9600_FILTER_TYPE_NONE;
> +
> +	return MCP9600_FILTER_TYPE_EMA;
> +}
> +
> +static int mcp9600_set_filter(struct iio_dev *indio_dev,
> +			      struct iio_chan_spec const *chan,
> +			      unsigned int mode)
> +{
> +	struct mcp9600_data *data = iio_priv(indio_dev);
> +
> +	switch (mode) {
> +	case MCP9600_FILTER_TYPE_NONE:
> +		data->filter_level = 0;

Don't touch data->filter_level here, just set data->is_filter_enabled = false.

> +		return mcp9600_config(data);
> +
> +	case MCP9600_FILTER_TYPE_EMA:
> +		if (data->filter_level == 0) {
> +			/* Minimum filter by default */
> +			data->filter_level = 1;

And similar, just set data->is_filter_enabled = true without changing filter_level.

> +			return mcp9600_config(data);
> +		}
> +		return 0;
> +
> +	default:
> +		return -EINVAL;
> +	}
> +}
> +
>  static int mcp9600_get_alert_index(int channel2, enum iio_event_direction dir)
>  {
>  	if (channel2 == IIO_MOD_TEMP_AMBIENT) {
> @@ -358,6 +512,9 @@ static int mcp9600_write_thresh(struct iio_dev *indio_dev,
>  
>  static const struct iio_info mcp9600_info = {
>  	.read_raw = mcp9600_read_raw,
> +	.read_avail = mcp9600_read_avail,
> +	.write_raw = mcp9600_write_raw,
> +	.write_raw_get_fmt = mcp9600_write_raw_get_fmt,
>  	.read_event_config = mcp9600_read_event_config,
>  	.write_event_config = mcp9600_write_event_config,
>  	.read_event_value = mcp9600_read_thresh,