iio: adc: ad7124: Add buffered input support

This patch adds the option to enable the buffered mode for positive and
negative inputs. Each option can be enabled independently.

In buffered mode, the input channel feeds into a high impedance input stage
of the buffer amplifier. Therefore, the input can tolerate significant
source impedances and is tailored for direct connection to external
resistive type sensors such as strain gages or RTDs.

Signed-off-by: Mircea Caprioru <mircea.caprioru@analog.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

diff --git a/drivers/iio/adc/ad7124.c b/drivers/iio/adc/ad7124.c
index 810234db9c0df232dea301b840d750b6a40feb6e..ab52c5e9ecb154995abd27546619b163e91737aa 100644 (file)
--- a/drivers/iio/adc/ad7124.c
+++ b/drivers/iio/adc/ad7124.c
@@ -61,6 +61,8 @@
 #define AD7124_CONFIG_REF_SEL(x)       FIELD_PREP(AD7124_CONFIG_REF_SEL_MSK, x)
 #define AD7124_CONFIG_PGA_MSK          GENMASK(2, 0)
 #define AD7124_CONFIG_PGA(x)           FIELD_PREP(AD7124_CONFIG_PGA_MSK, x)
+#define AD7124_CONFIG_IN_BUFF_MSK      GENMASK(7, 6)
+#define AD7124_CONFIG_IN_BUFF(x)       FIELD_PREP(AD7124_CONFIG_IN_BUFF_MSK, x)
 
 /* AD7124_FILTER_X */
 #define AD7124_FILTER_FS_MSK           GENMASK(10, 0)
@@ -108,6 +110,8 @@ struct ad7124_chip_info {
 struct ad7124_channel_config {
        enum ad7124_ref_sel refsel;
        bool bipolar;
+       bool buf_positive;
+       bool buf_negative;
        unsigned int ain;
        unsigned int vref_mv;
        unsigned int pga_bits;
@@ -473,6 +477,11 @@ static int ad7124_of_parse_channel_config(struct iio_dev *indio_dev,
                else
                        st->channel_config[channel].refsel = tmp;
 
+               st->channel_config[channel].buf_positive =
+                       of_property_read_bool(child, "adi,buffered-positive");
+               st->channel_config[channel].buf_negative =
+                       of_property_read_bool(child, "adi,buffered-negative");
+
                *chan = ad7124_channel_template;
                chan->address = channel;
                chan->scan_index = channel;
@@ -492,7 +501,7 @@ err:
 static int ad7124_setup(struct ad7124_state *st)
 {
        unsigned int val, fclk, power_mode;
-       int i, ret;
+       int i, ret, tmp;
 
        fclk = clk_get_rate(st->mclk);
        if (!fclk)
@@ -525,8 +534,12 @@ static int ad7124_setup(struct ad7124_state *st)
                if (ret < 0)
                        return ret;
 
+               tmp = (st->channel_config[i].buf_positive << 1)  +
+                       st->channel_config[i].buf_negative;
+
                val = AD7124_CONFIG_BIPOLAR(st->channel_config[i].bipolar) |
-                     AD7124_CONFIG_REF_SEL(st->channel_config[i].refsel);
+                     AD7124_CONFIG_REF_SEL(st->channel_config[i].refsel) |
+                     AD7124_CONFIG_IN_BUFF(tmp);
                ret = ad_sd_write_reg(&st->sd, AD7124_CONFIG(i), 2, val);
                if (ret < 0)
                        return ret;