[RFC PATCH 6/7] iio: adc: stm32-dfsdm: add scaling support to dfsdm

From: Olivier Moysan
Date: Fri Jun 23 2023 - 10:14:14 EST

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Add scaling support to STM32 DFSDM.

Signed-off-by: Olivier Moysan <olivier.moysan@xxxxxxxxxxx>
---
drivers/iio/adc/sd_adc_modulator.c | 31 ++++++++++++++-
drivers/iio/adc/stm32-dfsdm-adc.c | 64 ++++++++++++++++++++++++++++--
2 files changed, 91 insertions(+), 4 deletions(-)

diff --git a/drivers/iio/adc/sd_adc_modulator.c b/drivers/iio/adc/sd_adc_modulator.c
index 61246a52dc79..749c46da9c72 100644
--- a/drivers/iio/adc/sd_adc_modulator.c
+++ b/drivers/iio/adc/sd_adc_modulator.c
@@ -12,15 +12,23 @@
#include <linux/module.h>
#include <linux/mod_devicetable.h>
#include <linux/platform_device.h>
+#include <linux/regulator/consumer.h>

struct iio_sd_mod_priv {
+ struct regulator *vref;
+ int vref_mv;
};

static int sd_mod_enable(struct iio_backend *backend)
{
struct iio_sd_mod_priv *priv = backend->priv;
+ int ret;

/* PM resume */
+ ret = regulator_enable(priv->vref);
+
+ ret = regulator_get_voltage(priv->vref);
+ priv->vref_mv = ret / 1000;

return 0;
};
@@ -30,6 +38,7 @@ static int sd_mod_disable(struct iio_backend *backend)
struct iio_sd_mod_priv *priv = backend->priv;

/* PM suspend */
+ regulator_disable(priv->vref);

return 0;
};
@@ -39,7 +48,15 @@ static int sd_mod_read(struct iio_backend *backend, int *val, int *val2, long ma
struct iio_sd_mod_priv *priv = backend->priv;

switch (mask) {
- /* Process channel info */
+ case IIO_CHAN_INFO_SCALE:
+ *val = priv->vref_mv;
+ *val2 = 0;
+ return IIO_VAL_INT;
+
+ case IIO_CHAN_INFO_OFFSET:
+ *val = 0;
+ *val2 = 0;
+ return IIO_VAL_INT;
}

return -EINVAL;
@@ -54,12 +71,24 @@ static const struct iio_backend_ops sd_mod_ops = {
static int iio_sd_mod_probe(struct platform_device *pdev)
{
struct device *dev = &pdev->dev;
+ struct regulator *vref;
struct iio_backend *backend;
struct iio_sd_mod_priv *priv;
int ret;

priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);

+ vref = devm_regulator_get_optional(dev, "vref");
+ if (IS_ERR(vref)) {
+ ret = PTR_ERR(vref);
+ if (ret != -ENODEV) {
+ if (ret != -EPROBE_DEFER)
+ dev_err(dev, "vref get failed, %d\n", ret);
+ return ret;
+ }
+ }
+ priv->vref = vref;
+
backend = iio_backend_alloc(dev);

backend->priv = priv;
diff --git a/drivers/iio/adc/stm32-dfsdm-adc.c b/drivers/iio/adc/stm32-dfsdm-adc.c
index 2e76497cee51..468d72ab079d 100644
--- a/drivers/iio/adc/stm32-dfsdm-adc.c
+++ b/drivers/iio/adc/stm32-dfsdm-adc.c
@@ -9,6 +9,7 @@
#include <linux/dmaengine.h>
#include <linux/dma-mapping.h>
#include <linux/iio/adc/stm32-dfsdm-adc.h>
+#include <linux/iio/backend.h>
#include <linux/iio/buffer.h>
#include <linux/iio/hw-consumer.h>
#include <linux/iio/sysfs.h>
@@ -76,6 +77,7 @@ struct stm32_dfsdm_adc {

/* ADC specific */
unsigned int oversamp;
+ struct iio_backend **backend;
struct completion completion;
u32 *buffer;

@@ -599,6 +601,8 @@ static int stm32_dfsdm_channel_parse_of(struct stm32_dfsdm *dfsdm,
struct iio_chan_spec *ch)
{
struct stm32_dfsdm_channel *df_ch;
+ struct stm32_dfsdm_adc *adc = iio_priv(indio_dev);
+ struct iio_backend *backend;
const char *of_str;
int ret, val;

@@ -647,6 +651,9 @@ static int stm32_dfsdm_channel_parse_of(struct stm32_dfsdm *dfsdm,
if (ret != -EINVAL)
df_ch->alt_si = 0;

+ backend = iio_backend_get(node->dev);
+ adc->backend[df_ch->id] = backend;
+
return 0;
}

@@ -1090,7 +1097,7 @@ static int stm32_dfsdm_single_conv(struct iio_dev *indio_dev,
{
struct stm32_dfsdm_adc *adc = iio_priv(indio_dev);
long timeout;
- int ret;
+ int ret, idx = chan->scan_index;

reinit_completion(&adc->completion);

@@ -1100,6 +1107,8 @@ static int stm32_dfsdm_single_conv(struct iio_dev *indio_dev,
if (ret < 0)
return ret;

+ adc->backend[idx]->ops->enable(adc->backend[idx]);
+
ret = regmap_update_bits(adc->dfsdm->regmap, DFSDM_CR2(adc->fl_id),
DFSDM_CR2_REOCIE_MASK, DFSDM_CR2_REOCIE(1));
if (ret < 0)
@@ -1133,6 +1142,8 @@ static int stm32_dfsdm_single_conv(struct iio_dev *indio_dev,
stm32_dfsdm_process_data(adc, res);

stop_dfsdm:
+ adc->backend[idx]->ops->disable(adc->backend[idx]);
+
stm32_dfsdm_stop_dfsdm(adc->dfsdm);

return ret;
@@ -1197,7 +1208,14 @@ 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;
+
+ if (flo->lshift < chan->scan_type.shift)
+ max = flo->max >> (chan->scan_type.shift - flo->lshift);

switch (mask) {
case IIO_CHAN_INFO_RAW:
@@ -1231,6 +1249,41 @@ 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
+ */
+ adc->backend[idx]->ops->read_raw(adc->backend[idx], val, val2, mask);
+
+ *val = div_u64((u64)*val * (u64)BIT(DFSDM_DATA_RES - 1), max);
+ *val2 = chan->scan_type.realbits;
+ if (chan->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.
+ */
+ adc->backend[idx]->ops->read_raw(adc->backend[idx], val, val2, mask);
+
+ *val = div_u64((u64)max * *val, BIT(*val2 - 1));
+ if (chan->differential)
+ *val += max;
+ return IIO_VAL_INT;
}

return -EINVAL;
@@ -1358,7 +1411,10 @@ 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);

@@ -1454,6 +1510,8 @@ static int stm32_dfsdm_adc_init(struct device *dev, struct iio_dev *indio_dev)
if (ret < 0)
return ret;

+ adc->backend = devm_kzalloc(&indio_dev->dev, sizeof(*adc->backend) * num_ch, GFP_KERNEL);
+
indio_dev->num_channels = num_ch;
indio_dev->channels = ch;

--
2.25.1

Next message: Ard Biesheuvel: "Re: [PATCH v2 1/3] Documentation: arm: Add bootargs to the table of added DT parameters"
Previous message: Gustavo A. R. Silva: "Re: [PATCH][next] MIPS: dec: prom: Address -Warray-bounds warning"
In reply to: Olivier Moysan: "[RFC PATCH 7/7] ARM: dts: stm32: add dfsdm iio suppport"
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