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Message-Id: <20241217-ad4695-oversampling-v1-1-0b045d835dac@baylibre.com>
Date: Tue, 17 Dec 2024 16:47:28 -0500
From: Trevor Gamblin <tgamblin@...libre.com>
To: Michael Hennerich <michael.hennerich@...log.com>,
Nuno Sá <nuno.sa@...log.com>,
David Lechner <dlechner@...libre.com>, Lars-Peter Clausen <lars@...afoo.de>,
Jonathan Cameron <jic23@...nel.org>, Jonathan Corbet <corbet@....net>
Cc: linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-doc@...r.kernel.org, Trevor Gamblin <tgamblin@...libre.com>
Subject: [PATCH 1/2] iio: adc: ad4695: add offload-based oversampling
support
Add support for the ad4695's oversampling feature when SPI offload is
available. This allows the ad4695 to set oversampling ratios on a
per-channel basis, raising the effective-number-of-bits from 16
(OSR == 1) to 17 (4), 18 (16), or 19 (64) for a given sample (i.e. one
full cycle through the auto-sequencer). The logic for reading and
writing sampling frequency for a given channel is also adjusted based on
the current oversampling ratio.
The non-offload case isn't supported as there isn't a good way to
trigger the CNV pin in this mode. Support could be added in the future
if a use-case arises.
Signed-off-by: Trevor Gamblin <tgamblin@...libre.com>
---
drivers/iio/adc/ad4695.c | 378 +++++++++++++++++++++++++++++++++++++++++++----
1 file changed, 348 insertions(+), 30 deletions(-)
diff --git a/drivers/iio/adc/ad4695.c b/drivers/iio/adc/ad4695.c
index c8cd73d19e86..320f2c1a0877 100644
--- a/drivers/iio/adc/ad4695.c
+++ b/drivers/iio/adc/ad4695.c
@@ -79,6 +79,7 @@
#define AD4695_REG_CONFIG_IN_MODE BIT(6)
#define AD4695_REG_CONFIG_IN_PAIR GENMASK(5, 4)
#define AD4695_REG_CONFIG_IN_AINHIGHZ_EN BIT(3)
+#define AD4695_REG_CONFIG_IN_OSR_SET GENMASK(1, 0)
#define AD4695_REG_UPPER_IN(n) (0x0040 | (2 * (n)))
#define AD4695_REG_LOWER_IN(n) (0x0060 | (2 * (n)))
#define AD4695_REG_HYST_IN(n) (0x0080 | (2 * (n)))
@@ -127,6 +128,7 @@ struct ad4695_channel_config {
bool bipolar;
enum ad4695_in_pair pin_pairing;
unsigned int common_mode_mv;
+ unsigned int oversampling_ratio;
};
struct ad4695_state {
@@ -306,6 +308,65 @@ static const struct regmap_bus ad4695_regmap_bus = {
.val_format_endian_default = REGMAP_ENDIAN_BIG,
};
+enum {
+ AD4695_SCAN_TYPE_OSR_1,
+ AD4695_SCAN_TYPE_OSR_4,
+ AD4695_SCAN_TYPE_OSR_16,
+ AD4695_SCAN_TYPE_OSR_64,
+};
+
+static const struct iio_scan_type ad4695_scan_type_offload_u[] = {
+ [AD4695_SCAN_TYPE_OSR_1] = {
+ .sign = 'u',
+ .realbits = 16,
+ .shift = 3,
+ .storagebits = 32,
+ },
+ [AD4695_SCAN_TYPE_OSR_4] = {
+ .sign = 'u',
+ .realbits = 17,
+ .shift = 2,
+ .storagebits = 32,
+ },
+ [AD4695_SCAN_TYPE_OSR_16] = {
+ .sign = 'u',
+ .realbits = 18,
+ .shift = 1,
+ .storagebits = 32,
+ },
+ [AD4695_SCAN_TYPE_OSR_64] = {
+ .sign = 'u',
+ .realbits = 19,
+ .storagebits = 32,
+ },
+};
+
+static const struct iio_scan_type ad4695_scan_type_offload_s[] = {
+ [AD4695_SCAN_TYPE_OSR_1] = {
+ .sign = 's',
+ .realbits = 16,
+ .shift = 3,
+ .storagebits = 32,
+ },
+ [AD4695_SCAN_TYPE_OSR_4] = {
+ .sign = 's',
+ .realbits = 17,
+ .shift = 2,
+ .storagebits = 32,
+ },
+ [AD4695_SCAN_TYPE_OSR_16] = {
+ .sign = 's',
+ .realbits = 18,
+ .shift = 1,
+ .storagebits = 32,
+ },
+ [AD4695_SCAN_TYPE_OSR_64] = {
+ .sign = 's',
+ .realbits = 19,
+ .storagebits = 32,
+ },
+};
+
static const struct iio_chan_spec ad4695_channel_template = {
.type = IIO_VOLTAGE,
.indexed = 1,
@@ -343,6 +404,10 @@ static const char * const ad4695_power_supplies[] = {
"avdd", "vio"
};
+static const int ad4695_oversampling_ratios[] = {
+ 1, 4, 16, 64,
+};
+
static const struct ad4695_chip_info ad4695_chip_info = {
.name = "ad4695",
.max_sample_rate = 500 * KILO,
@@ -519,6 +584,29 @@ static int ad4695_set_ref_voltage(struct ad4695_state *st, int vref_mv)
FIELD_PREP(AD4695_REG_REF_CTRL_VREF_SET, val));
}
+/**
+ * ad4695_osr_to_regval - convert ratio to OSR register value
+ * @ratio: ratio to check
+ *
+ * Check if ratio is present in the list of available ratios and return
+ * the corresponding value that needs to be written to the register to
+ * select that ratio.
+ *
+ * Returns: register value (0 to 3) or -EINVAL if there is not an exact
+ * match
+ */
+static int ad4695_osr_to_regval(int ratio)
+{
+ int i;
+
+ for (i = 0; i < ARRAY_SIZE(ad4695_oversampling_ratios); i++) {
+ if (ratio == ad4695_oversampling_ratios[i])
+ return i;
+ }
+
+ return -EINVAL;
+}
+
static int ad4695_write_chn_cfg(struct ad4695_state *st,
struct ad4695_channel_config *cfg)
{
@@ -945,10 +1033,18 @@ static int ad4695_read_raw(struct iio_dev *indio_dev,
int *val, int *val2, long mask)
{
struct ad4695_state *st = iio_priv(indio_dev);
+ const struct iio_scan_type *scan_type;
struct ad4695_channel_config *cfg = &st->channels_cfg[chan->scan_index];
- u8 realbits = chan->scan_type.realbits;
+ unsigned int osr = st->channels_cfg[chan->scan_index].oversampling_ratio;
unsigned int reg_val;
int ret, tmp;
+ u8 realbits;
+
+ scan_type = iio_get_current_scan_type(indio_dev, chan);
+ if (IS_ERR(scan_type))
+ return PTR_ERR(scan_type);
+
+ realbits = scan_type->realbits;
switch (mask) {
case IIO_CHAN_INFO_RAW:
@@ -957,7 +1053,7 @@ static int ad4695_read_raw(struct iio_dev *indio_dev,
if (ret)
return ret;
- if (chan->scan_type.sign == 's')
+ if (scan_type->sign == 's')
*val = sign_extend32(st->raw_data, realbits - 1);
else
*val = st->raw_data;
@@ -969,7 +1065,7 @@ static int ad4695_read_raw(struct iio_dev *indio_dev,
switch (chan->type) {
case IIO_VOLTAGE:
*val = st->vref_mv;
- *val2 = chan->scan_type.realbits;
+ *val2 = realbits;
return IIO_VAL_FRACTIONAL_LOG2;
case IIO_TEMP:
/* T_scale (°C) = raw * V_REF (mV) / (-1.8 mV/°C * 2^16) */
@@ -1030,8 +1126,26 @@ static int ad4695_read_raw(struct iio_dev *indio_dev,
tmp = sign_extend32(reg_val, 15);
- *val = tmp / 4;
- *val2 = abs(tmp) % 4 * MICRO / 4;
+ switch (cfg->oversampling_ratio) {
+ case 1:
+ *val = tmp / 4;
+ *val2 = abs(tmp) % 4 * MICRO / 4;
+ break;
+ case 4:
+ *val = tmp / 2;
+ *val2 = abs(tmp) % 2 * MICRO / 2;
+ break;
+ case 16:
+ *val = tmp;
+ *val2 = 0;
+ break;
+ case 64:
+ *val = tmp * 2;
+ *val2 = 0;
+ break;
+ default:
+ return -EINVAL;
+ }
if (tmp < 0 && *val2) {
*val *= -1;
@@ -1044,6 +1158,14 @@ static int ad4695_read_raw(struct iio_dev *indio_dev,
default:
return -EINVAL;
}
+ case IIO_CHAN_INFO_OVERSAMPLING_RATIO:
+ switch (chan->type) {
+ case IIO_VOLTAGE:
+ *val = st->channels_cfg[chan->scan_index].oversampling_ratio;
+ return IIO_VAL_INT;
+ default:
+ return -EINVAL;
+ }
case IIO_CHAN_INFO_SAMP_FREQ: {
struct pwm_state state;
@@ -1051,7 +1173,11 @@ static int ad4695_read_raw(struct iio_dev *indio_dev,
if (ret)
return ret;
- *val = DIV_ROUND_UP_ULL(NSEC_PER_SEC, state.period);
+ /*
+ * The effective sampling frequency for a channel is the input
+ * frequency divided by the channel's OSR value.
+ */
+ *val = DIV_ROUND_UP_ULL(NSEC_PER_SEC, state.period * osr);
return IIO_VAL_INT;
}
@@ -1072,12 +1198,114 @@ static int ad4695_write_raw_get_fmt(struct iio_dev *indio_dev,
}
}
+static int ad4695_set_osr_val(struct ad4695_state *st,
+ struct iio_chan_spec const *chan,
+ int val)
+{
+ int osr = ad4695_osr_to_regval(val);
+
+ if (osr < 0)
+ return osr;
+
+ switch (chan->type) {
+ case IIO_VOLTAGE:
+ st->channels_cfg[chan->scan_index].oversampling_ratio = val;
+ return regmap_update_bits(st->regmap,
+ AD4695_REG_CONFIG_IN(chan->scan_index),
+ AD4695_REG_CONFIG_IN_OSR_SET,
+ FIELD_PREP(AD4695_REG_CONFIG_IN_OSR_SET, osr));
+ default:
+ return -EINVAL;
+ }
+}
+
+static unsigned int ad4695_get_calibbias(int val, int val2, int osr)
+{
+ unsigned int reg_val;
+
+ switch (osr) {
+ case 4:
+ if (val2 >= 0 && val > S16_MAX / 2)
+ reg_val = S16_MAX;
+ else if ((val2 < 0 ? -val : val) < S16_MIN / 2)
+ reg_val = S16_MIN;
+ else if (val2 < 0)
+ reg_val = clamp_t(int,
+ -(val * 2 + -val2 * 2 / MICRO),
+ S16_MIN, S16_MAX);
+ else if (val < 0)
+ reg_val = clamp_t(int,
+ val * 2 - val2 * 2 / MICRO,
+ S16_MIN, S16_MAX);
+ else
+ reg_val = clamp_t(int,
+ val * 2 + val2 * 2 / MICRO,
+ S16_MIN, S16_MAX);
+ return reg_val;
+ case 16:
+ if (val2 >= 0 && val > S16_MAX)
+ reg_val = S16_MAX;
+ else if ((val2 < 0 ? -val : val) < S16_MIN)
+ reg_val = S16_MIN;
+ else if (val2 < 0)
+ reg_val = clamp_t(int,
+ -(val + -val2 / MICRO),
+ S16_MIN, S16_MAX);
+ else if (val < 0)
+ reg_val = clamp_t(int,
+ val - val2 / MICRO,
+ S16_MIN, S16_MAX);
+ else
+ reg_val = clamp_t(int,
+ val + val2 / MICRO,
+ S16_MIN, S16_MAX);
+ return reg_val;
+ case 64:
+ if (val2 >= 0 && val > S16_MAX * 2)
+ reg_val = S16_MAX;
+ else if ((val2 < 0 ? -val : val) < S16_MIN * 2)
+ reg_val = S16_MIN;
+ else if (val2 < 0)
+ reg_val = clamp_t(int,
+ -(val / 2 + -val2 / 2 / MICRO),
+ S16_MIN, S16_MAX);
+ else if (val < 0)
+ reg_val = clamp_t(int,
+ val / 2 - val2 / 2 / MICRO,
+ S16_MIN, S16_MAX);
+ else
+ reg_val = clamp_t(int,
+ val / 2 + val2 / 2 / MICRO,
+ S16_MIN, S16_MAX);
+ return reg_val;
+ default:
+ if (val2 >= 0 && val > S16_MAX / 4)
+ reg_val = S16_MAX;
+ else if ((val2 < 0 ? -val : val) < S16_MIN / 4)
+ reg_val = S16_MIN;
+ else if (val2 < 0)
+ reg_val = clamp_t(int,
+ -(val * 4 + -val2 * 4 / MICRO),
+ S16_MIN, S16_MAX);
+ else if (val < 0)
+ reg_val = clamp_t(int,
+ val * 4 - val2 * 4 / MICRO,
+ S16_MIN, S16_MAX);
+ else
+ reg_val = clamp_t(int,
+ val * 4 + val2 * 4 / MICRO,
+ S16_MIN, S16_MAX);
+ return reg_val;
+ }
+}
+
static int ad4695_write_raw(struct iio_dev *indio_dev,
struct iio_chan_spec const *chan,
int val, int val2, long mask)
{
struct ad4695_state *st = iio_priv(indio_dev);
unsigned int reg_val;
+ unsigned int osr = st->channels_cfg[chan->scan_index].oversampling_ratio;
iio_device_claim_direct_scoped(return -EBUSY, indio_dev) {
switch (mask) {
@@ -1102,23 +1330,7 @@ static int ad4695_write_raw(struct iio_dev *indio_dev,
case IIO_CHAN_INFO_CALIBBIAS:
switch (chan->type) {
case IIO_VOLTAGE:
- if (val2 >= 0 && val > S16_MAX / 4)
- reg_val = S16_MAX;
- else if ((val2 < 0 ? -val : val) < S16_MIN / 4)
- reg_val = S16_MIN;
- else if (val2 < 0)
- reg_val = clamp_t(int,
- -(val * 4 + -val2 * 4 / MICRO),
- S16_MIN, S16_MAX);
- else if (val < 0)
- reg_val = clamp_t(int,
- val * 4 - val2 * 4 / MICRO,
- S16_MIN, S16_MAX);
- else
- reg_val = clamp_t(int,
- val * 4 + val2 * 4 / MICRO,
- S16_MIN, S16_MAX);
-
+ reg_val = ad4695_get_calibbias(val, val2, osr);
return regmap_write(st->regmap16,
AD4695_REG_OFFSET_IN(chan->scan_index),
reg_val);
@@ -1127,15 +1339,27 @@ static int ad4695_write_raw(struct iio_dev *indio_dev,
}
case IIO_CHAN_INFO_SAMP_FREQ: {
struct pwm_state state;
-
- if (val <= 0 || val > st->chip_info->max_sample_rate)
+ /*
+ * Limit the maximum acceptable sample rate according to
+ * the channel's oversampling ratio.
+ */
+ u64 max_osr_rate = DIV_ROUND_UP_ULL(st->chip_info->max_sample_rate,
+ osr);
+
+ if (val <= 0 || val > max_osr_rate)
return -EINVAL;
guard(mutex)(&st->cnv_pwm_lock);
pwm_get_state(st->cnv_pwm, &state);
- state.period = DIV_ROUND_UP_ULL(NSEC_PER_SEC, val);
+ /*
+ * The required sample frequency for a given OSR is the
+ * input frequency multiplied by it.
+ */
+ state.period = DIV_ROUND_UP_ULL(NSEC_PER_SEC, val * osr);
return pwm_apply_might_sleep(st->cnv_pwm, &state);
}
+ case IIO_CHAN_INFO_OVERSAMPLING_RATIO:
+ return ad4695_set_osr_val(st, chan, val);
default:
return -EINVAL;
}
@@ -1148,18 +1372,40 @@ static int ad4695_read_avail(struct iio_dev *indio_dev,
const int **vals, int *type, int *length,
long mask)
{
+ int ret;
static const int ad4695_calibscale_available[6] = {
/* Range of 0 (inclusive) to 2 (exclusive) */
0, 15, 1, 15, U16_MAX, 15
};
- static const int ad4695_calibbias_available[6] = {
+ static const int ad4695_calibbias_available[4][6] = {
/*
* Datasheet says FSR/8 which translates to signed/4. The step
- * depends on oversampling ratio which is always 1 for now.
+ * depends on oversampling ratio, so we need four different
+ * ranges to select from.
*/
- S16_MIN / 4, 0, 0, MICRO / 4, S16_MAX / 4, S16_MAX % 4 * MICRO / 4
+ {
+ S16_MIN / 4, 0,
+ 0, MICRO / 4,
+ S16_MAX / 4, S16_MAX % 4 * MICRO / 4
+ },
+ {
+ S16_MIN / 2, 0,
+ 0, MICRO / 2,
+ S16_MAX / 2, S16_MAX % 2 * MICRO / 2,
+ },
+ {
+ S16_MIN, 0,
+ 1, 0,
+ S16_MAX, 0,
+ },
+ {
+ S16_MIN * 2, 0,
+ 2, 0,
+ S16_MAX * 2, 0,
+ },
};
struct ad4695_state *st = iio_priv(indio_dev);
+ unsigned int osr = st->channels_cfg[chan->scan_index].oversampling_ratio;
switch (mask) {
case IIO_CHAN_INFO_CALIBSCALE:
@@ -1174,16 +1420,36 @@ static int ad4695_read_avail(struct iio_dev *indio_dev,
case IIO_CHAN_INFO_CALIBBIAS:
switch (chan->type) {
case IIO_VOLTAGE:
- *vals = ad4695_calibbias_available;
+ ret = ad4695_osr_to_regval(osr);
+ if (ret < 0)
+ return ret;
+ /*
+ * Select the appropriate calibbias array based on the
+ * OSR value in the register.
+ */
+ *vals = ad4695_calibbias_available[ret];
*type = IIO_VAL_INT_PLUS_MICRO;
return IIO_AVAIL_RANGE;
default:
return -EINVAL;
}
case IIO_CHAN_INFO_SAMP_FREQ:
+ /* Max sample rate for the channel depends on OSR */
+ st->sample_freq_range[2] =
+ DIV_ROUND_UP_ULL(st->chip_info->max_sample_rate, osr);
*vals = st->sample_freq_range;
*type = IIO_VAL_INT;
return IIO_AVAIL_RANGE;
+ case IIO_CHAN_INFO_OVERSAMPLING_RATIO:
+ switch (chan->type) {
+ case IIO_VOLTAGE:
+ *vals = ad4695_oversampling_ratios;
+ *length = ARRAY_SIZE(ad4695_oversampling_ratios);
+ *type = IIO_VAL_INT;
+ return IIO_AVAIL_LIST;
+ default:
+ return -EINVAL;
+ }
default:
return -EINVAL;
}
@@ -1217,6 +1483,26 @@ static int ad4695_debugfs_reg_access(struct iio_dev *indio_dev,
return -EINVAL;
}
+static int ad4695_get_current_scan_type(const struct iio_dev *indio_dev,
+ const struct iio_chan_spec *chan)
+{
+ struct ad4695_state *st = iio_priv(indio_dev);
+ unsigned int osr = st->channels_cfg[chan->scan_index].oversampling_ratio;
+
+ switch (osr) {
+ case 1:
+ return AD4695_SCAN_TYPE_OSR_1;
+ case 4:
+ return AD4695_SCAN_TYPE_OSR_4;
+ case 16:
+ return AD4695_SCAN_TYPE_OSR_16;
+ case 64:
+ return AD4695_SCAN_TYPE_OSR_64;
+ default:
+ return -EINVAL;
+ }
+}
+
static const struct iio_info ad4695_info = {
.read_raw = &ad4695_read_raw,
.write_raw_get_fmt = &ad4695_write_raw_get_fmt,
@@ -1225,6 +1511,15 @@ static const struct iio_info ad4695_info = {
.debugfs_reg_access = &ad4695_debugfs_reg_access,
};
+static const struct iio_info ad4695_offload_info = {
+ .read_raw = &ad4695_read_raw,
+ .write_raw_get_fmt = &ad4695_write_raw_get_fmt,
+ .write_raw = &ad4695_write_raw,
+ .get_current_scan_type = &ad4695_get_current_scan_type,
+ .read_avail = &ad4695_read_avail,
+ .debugfs_reg_access = &ad4695_debugfs_reg_access,
+};
+
static int ad4695_parse_channel_cfg(struct ad4695_state *st)
{
struct device *dev = &st->spi->dev;
@@ -1240,6 +1535,9 @@ static int ad4695_parse_channel_cfg(struct ad4695_state *st)
chan_cfg->highz_en = true;
chan_cfg->channel = i;
+ /* This is the default OSR after reset */
+ chan_cfg->oversampling_ratio = 1;
+
*iio_chan = ad4695_channel_template;
iio_chan->channel = i;
iio_chan->scan_index = i;
@@ -1408,6 +1706,7 @@ static int ad4695_probe_spi_offload(struct iio_dev *indio_dev,
struct dma_chan *rx_dma;
int ret, i;
+ indio_dev->info = &ad4695_offload_info;
indio_dev->num_channels = st->chip_info->num_voltage_inputs + 1;
indio_dev->setup_ops = &ad4695_offload_buffer_setup_ops;
@@ -1458,6 +1757,7 @@ static int ad4695_probe_spi_offload(struct iio_dev *indio_dev,
for (i = 0; i < indio_dev->num_channels; i++) {
struct iio_chan_spec *chan = &st->iio_chan[i];
+ struct ad4695_channel_config *cfg = &st->channels_cfg[i];
/*
* NB: When using offload support, all channels need to have the
@@ -1473,6 +1773,24 @@ static int ad4695_probe_spi_offload(struct iio_dev *indio_dev,
/* add sample frequency for PWM CNV trigger */
chan->info_mask_separate |= BIT(IIO_CHAN_INFO_SAMP_FREQ);
chan->info_mask_separate_available |= BIT(IIO_CHAN_INFO_SAMP_FREQ);
+
+ /* Add the oversampling properties only for voltage channels */
+ if (chan->type != IIO_VOLTAGE)
+ continue;
+
+ chan->info_mask_separate |= BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO);
+ chan->info_mask_separate_available |=
+ BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO);
+ chan->has_ext_scan_type = 1;
+ if (cfg->bipolar) {
+ chan->ext_scan_type = ad4695_scan_type_offload_s;
+ chan->num_ext_scan_type =
+ ARRAY_SIZE(ad4695_scan_type_offload_s);
+ } else {
+ chan->ext_scan_type = ad4695_scan_type_offload_u;
+ chan->num_ext_scan_type =
+ ARRAY_SIZE(ad4695_scan_type_offload_u);
+ }
}
return devm_iio_dmaengine_buffer_setup_with_handle(dev, indio_dev,
--
2.39.5
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