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Subject[PATCH] iio: adc: ad7124: add 3db filter
Date
This patch adds the LOW_PASS_FILTER_3DB_FREQUENCY attribute
in iio_chan_spec for each channel. The used filters are sinc3
or sinc4. The filter type with the highest output data rate
is used when setting a low pass frequency in the channel's sysfs.

Signed-off-by: Alexandru Tachici <alexandru.tachici@analog.com>
---
drivers/iio/adc/ad7124.c | 69 +++++++++++++++++++++++++++++++++++++++-
1 file changed, 68 insertions(+), 1 deletion(-)

diff --git a/drivers/iio/adc/ad7124.c b/drivers/iio/adc/ad7124.c
index 52f45b13da4a..8f48c0581f02 100644
--- a/drivers/iio/adc/ad7124.c
+++ b/drivers/iio/adc/ad7124.c
@@ -70,6 +70,11 @@
/* AD7124_FILTER_X */
#define AD7124_FILTER_FS_MSK GENMASK(10, 0)
#define AD7124_FILTER_FS(x) FIELD_PREP(AD7124_FILTER_FS_MSK, x)
+#define AD7124_FILTER_TYPE_MSK GENMASK(23, 21)
+#define AD7124_FILTER_TYPE_SEL(x) FIELD_PREP(AD7124_FILTER_TYPE_MSK, x)
+
+#define AD7124_SINC3_FILTER 2
+#define AD7124_SINC4_FILTER 0

enum ad7124_ids {
ID_AD7124_4,
@@ -119,6 +124,7 @@ struct ad7124_channel_config {
unsigned int vref_mv;
unsigned int pga_bits;
unsigned int odr;
+ unsigned int filter_type;
};

struct ad7124_state {
@@ -138,7 +144,8 @@ static const struct iio_chan_spec ad7124_channel_template = {
.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
BIT(IIO_CHAN_INFO_SCALE) |
BIT(IIO_CHAN_INFO_OFFSET) |
- BIT(IIO_CHAN_INFO_SAMP_FREQ),
+ BIT(IIO_CHAN_INFO_SAMP_FREQ) |
+ BIT(IIO_CHAN_INFO_LOW_PASS_FILTER_3DB_FREQUENCY),
.scan_type = {
.sign = 'u',
.realbits = 24,
@@ -281,6 +288,58 @@ static int ad7124_set_channel_gain(struct ad7124_state *st,
return 0;
}

+static int ad7124_get_3db_filter_freq(struct ad7124_state *st,
+ unsigned int channel)
+{
+ unsigned int fadc;
+
+ fadc = st->channel_config[channel].odr;
+
+ switch (st->channel_config[channel].filter_type) {
+ case AD7124_SINC3_FILTER:
+ return DIV_ROUND_CLOSEST(fadc * 230, 1000);
+ case AD7124_SINC4_FILTER:
+ return DIV_ROUND_CLOSEST(fadc * 262, 1000);
+ default:
+ return -EINVAL;
+ }
+}
+
+static int ad7124_set_3db_filter_freq(struct ad7124_state *st,
+ unsigned int channel,
+ unsigned int freq)
+{
+ unsigned int sinc4_3db_odr;
+ unsigned int sinc3_3db_odr;
+ unsigned int new_filter;
+ unsigned int new_odr;
+
+ sinc4_3db_odr = DIV_ROUND_CLOSEST(freq * 1000, 230);
+ sinc3_3db_odr = DIV_ROUND_CLOSEST(freq * 1000, 262);
+
+ if (sinc4_3db_odr > sinc3_3db_odr) {
+ new_filter = AD7124_SINC3_FILTER;
+ new_odr = sinc4_3db_odr;
+ } else {
+ new_filter = AD7124_SINC4_FILTER;
+ new_odr = sinc3_3db_odr;
+ }
+
+ if (st->channel_config[channel].filter_type != new_filter) {
+ int ret;
+
+ st->channel_config[channel].filter_type = new_filter;
+ ret = ad7124_spi_write_mask(st, AD7124_FILTER(channel),
+ AD7124_FILTER_TYPE_MSK,
+ AD7124_FILTER_TYPE_SEL(new_filter),
+ 3);
+ if (ret < 0)
+ return ret;
+ }
+
+ return ad7124_set_channel_odr(st, channel, new_odr);
+}
+
static int ad7124_read_raw(struct iio_dev *indio_dev,
struct iio_chan_spec const *chan,
int *val, int *val2, long info)
@@ -322,6 +381,9 @@ static int ad7124_read_raw(struct iio_dev *indio_dev,
case IIO_CHAN_INFO_SAMP_FREQ:
*val = st->channel_config[chan->address].odr;

+ return IIO_VAL_INT;
+ case IIO_CHAN_INFO_LOW_PASS_FILTER_3DB_FREQUENCY:
+ *val = ad7124_get_3db_filter_freq(st, chan->scan_index);
return IIO_VAL_INT;
default:
return -EINVAL;
@@ -355,6 +417,11 @@ static int ad7124_write_raw(struct iio_dev *indio_dev,
gain = DIV_ROUND_CLOSEST(res, val2);

return ad7124_set_channel_gain(st, chan->address, gain);
+ case IIO_CHAN_INFO_LOW_PASS_FILTER_3DB_FREQUENCY:
+ if (val2 != 0)
+ return -EINVAL;
+
+ return ad7124_set_3db_filter_freq(st, chan->address, val);
default:
return -EINVAL;
}
--
2.20.1
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