[PATCH 4/4] iio: adc: stm32-dfsdm: add scale and offset support

Olivier Moysan
2020-02-04T10:11:18Z

Add scale and offset attributes support to STM32 DFSDM.

Signed-off-by: Olivier Moysan <olivier.moysan@st.com>
---
drivers/iio/adc/stm32-dfsdm-adc.c | 105 +++++++++++++++++++++++++++++-
1 file changed, 102 insertions(+), 3 deletions(-)

diff --git a/drivers/iio/adc/stm32-dfsdm-adc.c b/drivers/iio/adc/stm32-dfsdm-adc.c
index 07b9dfdf8e76..b85fd3e90496 100644
--- a/drivers/iio/adc/stm32-dfsdm-adc.c
+++ b/drivers/iio/adc/stm32-dfsdm-adc.c
@@ -10,6 +10,7 @@
#include <linux/dma-mapping.h>
#include <linux/iio/adc/stm32-dfsdm-adc.h>
#include <linux/iio/buffer.h>
+#include <linux/iio/consumer.h>
#include <linux/iio/hw-consumer.h>
#include <linux/iio/sysfs.h>
#include <linux/iio/timer/stm32-lptim-trigger.h>
@@ -67,6 +68,13 @@ struct stm32_dfsdm_dev_data {
const struct regmap_config *regmap_cfg;
};

+struct stm32_dfsdm_sd_chan_info {
+ int scale_val;
+ int scale_val2;
+ int offset;
+ unsigned int differential;
+};
+
struct stm32_dfsdm_adc {
struct stm32_dfsdm *dfsdm;
const struct stm32_dfsdm_dev_data *dev_data;
@@ -79,6 +87,7 @@ struct stm32_dfsdm_adc {
struct iio_hw_consumer *hwc;
struct completion completion;
u32 *buffer;
+ struct stm32_dfsdm_sd_chan_info *sd_chan;

/* Audio specific */
unsigned int spi_freq; /* SPI bus clock frequency */
@@ -1271,7 +1280,10 @@ static int stm32_dfsdm_read_raw(struct iio_dev *indio_dev,
int *val2, long mask)
{
struct stm32_dfsdm_adc *adc = iio_priv(indio_dev);
- int ret;
+ struct stm32_dfsdm_filter *fl = &adc->dfsdm->fl_list[adc->fl_id];
+ struct stm32_dfsdm_filter_osr *flo = &fl->flo[fl->fast];
+ u32 max = flo->max << (flo->lshift - chan->scan_type.shift);
+ int ret, idx = chan->scan_index;

switch (mask) {
case IIO_CHAN_INFO_RAW:
@@ -1307,6 +1319,41 @@ static int stm32_dfsdm_read_raw(struct iio_dev *indio_dev,
*val = adc->sample_freq;

return IIO_VAL_INT;
+
+ case IIO_CHAN_INFO_SCALE:
+ /*
+ * Scale is expressed in mV.
+ * When fast mode is disabled, actual resolution may be lower
+ * than 2^n, where n=realbits-1.
+ * This leads to underestimating input voltage. To
+ * compensate this deviation, the voltage reference can be
+ * corrected with a factor = realbits resolution / actual max
+ */
+ *val = div_u64((u64)adc->sd_chan[idx].scale_val *
+ (u64)BIT(DFSDM_DATA_RES - 1), max);
+ *val2 = chan->scan_type.realbits;
+ if (adc->sd_chan[idx].differential)
+ *val *= 2;
+
+ return IIO_VAL_FRACTIONAL_LOG2;
+
+ case IIO_CHAN_INFO_OFFSET:
+ /*
+ * DFSDM output data are in the range [-2^n,2^n-1],
+ * with n=realbits-1.
+ * - Differential modulator:
+ * Offset correspond to SD modulator offset.
+ * - Single ended modulator:
+ * Input is in [0V,Vref] range, where 0V corresponds to -2^n.
+ * Add 2^n to offset. (i.e. middle of input range)
+ * offset = offset(sd) * vref / res(sd) * max / vref.
+ */
+ *val = div_u64((u64)max * adc->sd_chan[idx].offset,
+ BIT(adc->sd_chan[idx].scale_val2 - 1));
+ if (!adc->sd_chan[idx].differential)
+ *val += max;
+
+ return IIO_VAL_INT;
}

return -EINVAL;
@@ -1430,7 +1477,9 @@ static int stm32_dfsdm_adc_chan_init_one(struct iio_dev *indio_dev,
* IIO_CHAN_INFO_RAW: used to compute regular conversion
* IIO_CHAN_INFO_OVERSAMPLING_RATIO: used to set oversampling
*/
- ch->info_mask_separate = BIT(IIO_CHAN_INFO_RAW);
+ ch->info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
+ BIT(IIO_CHAN_INFO_SCALE) |
+ BIT(IIO_CHAN_INFO_OFFSET);
ch->info_mask_shared_by_all = BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO) |
BIT(IIO_CHAN_INFO_SAMP_FREQ);

@@ -1481,8 +1530,10 @@ static int stm32_dfsdm_adc_init(struct iio_dev *indio_dev)
{
struct iio_chan_spec *ch;
struct stm32_dfsdm_adc *adc = iio_priv(indio_dev);
+ struct iio_channel *channels, *chan;
+ struct stm32_dfsdm_sd_chan_info *sd_chan;
int num_ch;
- int ret, chan_idx;
+ int ret, chan_idx, val2;

adc->oversamp = DFSDM_DEFAULT_OVERSAMPLING;
ret = stm32_dfsdm_compute_all_osrs(indio_dev, adc->oversamp);
@@ -1506,6 +1557,22 @@ static int stm32_dfsdm_adc_init(struct iio_dev *indio_dev)
if (!ch)
return -ENOMEM;

+ /* Get SD modulator channels */
+ channels = iio_channel_get_all(&indio_dev->dev);
+ if (IS_ERR(channels)) {
+ dev_err(&indio_dev->dev, "Failed to get channel %ld\n",
+ PTR_ERR(channels));
+ return PTR_ERR(channels);
+ }
+ chan = &channels[0];
+
+ adc->sd_chan = devm_kzalloc(&indio_dev->dev,
+ sizeof(*adc->sd_chan) * num_ch, GFP_KERNEL);
+ if (!adc->sd_chan)
+ return -ENOMEM;
+
+ sd_chan = adc->sd_chan;
+
for (chan_idx = 0; chan_idx < num_ch; chan_idx++) {
ch[chan_idx].scan_index = chan_idx;
ret = stm32_dfsdm_adc_chan_init_one(indio_dev, &ch[chan_idx]);
@@ -1513,6 +1580,38 @@ static int stm32_dfsdm_adc_init(struct iio_dev *indio_dev)
dev_err(&indio_dev->dev, "Channels init failed\n");
return ret;
}
+
+ if (!chan->indio_dev)
+ return -EINVAL;
+
+ ret = iio_read_channel_scale(chan, &sd_chan->scale_val,
+ &sd_chan->scale_val2);
+ if (ret < 0) {
+ dev_err(&indio_dev->dev,
+ "Failed to get channel %d scale\n", chan_idx);
+ return ret;
+ }
+
+ if (iio_channel_has_info(chan->channel, IIO_CHAN_INFO_OFFSET)) {
+ ret = iio_read_channel_offset(chan, &sd_chan->offset,
+ &val2);
+ if (ret < 0) {
+ dev_err(&indio_dev->dev,
+ "Failed to get channel %d offset\n",
+ chan_idx);
+ return ret;
+ }
+ }
+
+ sd_chan->differential = chan->channel->differential;
+
+ dev_dbg(&indio_dev->dev, "Channel %d %s scale ref=%d offset=%d",
+ chan_idx, chan->channel->differential ?
+ "differential" : "single-ended",
+ sd_chan->scale_val, sd_chan->offset);
+
+ chan++;
+ sd_chan++;
}

indio_dev->num_channels = num_ch;
--
2.17.1