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iio: adc: ltc2378: Enable high-speed data capture

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Make use of SPI transfer offloading to speed up data capture, enabling data
acquisition at faster sample rates (up to 2 MSPS).

Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Reviewed-by: David Lechner <dlechner@baylibre.com>
Signed-off-by: Marcelo Schmitt <marcelo.schmitt@analog.com>
Signed-off-by: Jonathan Cameron <jonathan.cameron@oss.qualcomm.com>
This commit is contained in:
Marcelo Schmitt 2026-07-27 18:31:16 -03:00 committed by Jonathan Cameron
parent 469eafdc69
commit b587716e8c
2 changed files with 407 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
drivers/iio/adc/Kconfig
View File

@ -948,6 +948,12 @@ config LTC2378
depends on SPI
depends on REGULATOR || COMPILE_TEST
depends on GPIOLIB
depends on PWM
select IIO_BUFFER
select IIO_BUFFER_DMA
select IIO_BUFFER_DMAENGINE
select SPI_OFFLOAD
select SPI_OFFLOAD_TRIGGER_PWM
help
Say yes here to build support for Analog Devices LTC2378-20 and
similar analog to digital converters.

404
drivers/iio/adc/ltc2378.c
View File

@ -16,16 +16,27 @@
#include <linux/device-id/of.h>
#include <linux/err.h>
#include <linux/gpio/consumer.h>
#include <linux/math64.h>
#include <linux/minmax.h>
#include <linux/module.h>
#include <linux/mutex.h>
#include <linux/regulator/consumer.h>
#include <linux/pwm.h>
#include <linux/spi/spi.h>
#include <linux/spi/offload/consumer.h>
#include <linux/spi/offload/types.h>
#include <linux/time64.h>
#include <linux/types.h>
#include <linux/units.h>
#include <linux/iio/buffer.h>
#include <linux/iio/buffer-dmaengine.h>
#include <linux/iio/iio.h>
#include <linux/iio/types.h>
#define LTC2378_TDSDOBUSYL_NS 5
#define LTC2378_TBUSYLH_NS 13
#define LTC2378_TCNV_HIGH_NS 20
#define LTC2378_MAX_DATA_WAIT_US 4 /* max(TBUSYLH + TCONV + TDSDOBUSYL) */
#define LTC2378_CHANNEL(_sign, _real_bits, _storage_bits) \
@ -54,9 +65,49 @@
#define LTC2378_PSEUDO_DIFF_CHANNEL(_real_bits) \
LTC2378_CHANNEL(0, _real_bits, (((_real_bits) > 16) ? 32 : 16))
#define LTC2378_OFFLOAD_CHANNEL(_sign, _real_bits, _storage_bits) \
{ \
.type = IIO_VOLTAGE, \
.indexed = 1, \
.differential = _sign, \
.channel = 0, \
.channel2 = _sign ? 1 : 0, \
.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) | \
BIT(IIO_CHAN_INFO_SCALE) | \
BIT(IIO_CHAN_INFO_SAMP_FREQ), \
.info_mask_separate_available = BIT(IIO_CHAN_INFO_SAMP_FREQ), \
.scan_index = 0, \
.scan_type = { \
.format = _sign ? IIO_SCAN_FORMAT_SIGNED_INT : \
IIO_SCAN_FORMAT_UNSIGNED_INT, \
.realbits = _real_bits, \
.storagebits = _storage_bits, \
.shift = 0, \
.endianness = IIO_CPU, \
}, \
}
/*
* Currently, the available offload hardware + DMA configuration only supports
* pushing 32-bit data elements to DMA IIO buffers in CPU endianness. For 16-bit
* precision parts, those 32-bit elements (in CPU endianness) contain 2 bytes
* with data and 2 bytes always zeroed out. Nevertheless, for the offload use
* case, the IIO buffer is configured for 32 storage bits in CPU endianness so
* data is correctly aligned in user space despite 2 out of the 4 bytes being
* zeros.
*/
#define LTC2378_OFFLOAD_DIFF_CHANNEL(_real_bits) \
LTC2378_OFFLOAD_CHANNEL(1, (_real_bits), 32)
#define LTC2378_OFFLOAD_PSEUDO_DIFF_CHANNEL(_real_bits) \
LTC2378_OFFLOAD_CHANNEL(0, (_real_bits), 32)
struct ltc2378_chip_info {
const char *name;
struct iio_chan_spec chan;
struct iio_chan_spec offload_chan;
unsigned int max_sample_rate_Hz;
unsigned int tconv_ns;
};
struct ltc2378_state {
@ -66,6 +117,15 @@ struct ltc2378_state {
struct mutex lock; /* Protect data acquisition cycle */
int ref_uV;
struct spi_transfer xfer;
struct spi_transfer offload_xfer;
struct spi_offload *offload;
struct spi_offload_trigger *offload_trigger;
struct pwm_waveform cnv_wf;
struct spi_message offload_msg;
struct spi_offload_trigger_config offload_trigger_config;
struct pwm_device *cnv_trigger;
unsigned int cnv_Hz;
unsigned int sample_freq_range[3];
/*
* DMA (thus cache coherency maintenance) requires the transfer buffers
@ -85,96 +145,153 @@ struct ltc2378_state {
static const struct ltc2378_chip_info ltc2364_16_chip_info = {
.name = "ltc2364-16",
.chan = LTC2378_PSEUDO_DIFF_CHANNEL(16),
.offload_chan = LTC2378_OFFLOAD_PSEUDO_DIFF_CHANNEL(16),
.max_sample_rate_Hz = 250 * HZ_PER_KHZ,
.tconv_ns = 3000,
};
static const struct ltc2378_chip_info ltc2364_18_chip_info = {
.name = "ltc2364-18",
.chan = LTC2378_PSEUDO_DIFF_CHANNEL(18),
.offload_chan = LTC2378_OFFLOAD_PSEUDO_DIFF_CHANNEL(18),
.max_sample_rate_Hz = 250 * HZ_PER_KHZ,
.tconv_ns = 3000,
};
static const struct ltc2378_chip_info ltc2367_16_chip_info = {
.name = "ltc2367-16",
.chan = LTC2378_PSEUDO_DIFF_CHANNEL(16),
.offload_chan = LTC2378_OFFLOAD_PSEUDO_DIFF_CHANNEL(16),
.max_sample_rate_Hz = 500 * HZ_PER_KHZ,
.tconv_ns = 1500,
};
static const struct ltc2378_chip_info ltc2367_18_chip_info = {
.name = "ltc2367-18",
.chan = LTC2378_PSEUDO_DIFF_CHANNEL(18),
.offload_chan = LTC2378_OFFLOAD_PSEUDO_DIFF_CHANNEL(18),
.max_sample_rate_Hz = 500 * HZ_PER_KHZ,
.tconv_ns = 1500,
};
static const struct ltc2378_chip_info ltc2368_16_chip_info = {
.name = "ltc2368-16",
.chan = LTC2378_PSEUDO_DIFF_CHANNEL(16),
.offload_chan = LTC2378_OFFLOAD_PSEUDO_DIFF_CHANNEL(16),
.max_sample_rate_Hz = 1 * HZ_PER_MHZ,
.tconv_ns = 527,
};
static const struct ltc2378_chip_info ltc2368_18_chip_info = {
.name = "ltc2368-18",
.chan = LTC2378_PSEUDO_DIFF_CHANNEL(18),
.offload_chan = LTC2378_OFFLOAD_PSEUDO_DIFF_CHANNEL(18),
.max_sample_rate_Hz = 1 * HZ_PER_MHZ,
.tconv_ns = 527,
};
static const struct ltc2378_chip_info ltc2369_18_chip_info = {
.name = "ltc2369-18",
.chan = LTC2378_PSEUDO_DIFF_CHANNEL(18),
.offload_chan = LTC2378_OFFLOAD_PSEUDO_DIFF_CHANNEL(18),
.max_sample_rate_Hz = 1600 * HZ_PER_KHZ,
.tconv_ns = 412,
};
static const struct ltc2378_chip_info ltc2370_16_chip_info = {
.name = "ltc2370-16",
.chan = LTC2378_PSEUDO_DIFF_CHANNEL(16),
.offload_chan = LTC2378_OFFLOAD_PSEUDO_DIFF_CHANNEL(16),
.max_sample_rate_Hz = 2 * HZ_PER_MHZ,
.tconv_ns = 322,
};
static const struct ltc2378_chip_info ltc2376_16_chip_info = {
.name = "ltc2376-16",
.chan = LTC2378_DIFF_CHANNEL(16),
.offload_chan = LTC2378_OFFLOAD_DIFF_CHANNEL(16),
.max_sample_rate_Hz = 250 * HZ_PER_KHZ,
.tconv_ns = 3000,
};
static const struct ltc2378_chip_info ltc2376_18_chip_info = {
.name = "ltc2376-18",
.chan = LTC2378_DIFF_CHANNEL(18),
.offload_chan = LTC2378_OFFLOAD_DIFF_CHANNEL(18),
.max_sample_rate_Hz = 250 * HZ_PER_KHZ,
.tconv_ns = 3000,
};
static const struct ltc2378_chip_info ltc2376_20_chip_info = {
.name = "ltc2376-20",
.chan = LTC2378_DIFF_CHANNEL(20),
.offload_chan = LTC2378_OFFLOAD_DIFF_CHANNEL(20),
.max_sample_rate_Hz = 250 * HZ_PER_KHZ,
.tconv_ns = 3000,
};
static const struct ltc2378_chip_info ltc2377_16_chip_info = {
.name = "ltc2377-16",
.chan = LTC2378_DIFF_CHANNEL(16),
.offload_chan = LTC2378_OFFLOAD_DIFF_CHANNEL(16),
.max_sample_rate_Hz = 500 * HZ_PER_KHZ,
.tconv_ns = 1500,
};
static const struct ltc2378_chip_info ltc2377_18_chip_info = {
.name = "ltc2377-18",
.chan = LTC2378_DIFF_CHANNEL(18),
.offload_chan = LTC2378_OFFLOAD_DIFF_CHANNEL(18),
.max_sample_rate_Hz = 500 * HZ_PER_KHZ,
.tconv_ns = 1500,
};
static const struct ltc2378_chip_info ltc2377_20_chip_info = {
.name = "ltc2377-20",
.chan = LTC2378_DIFF_CHANNEL(20),
.offload_chan = LTC2378_OFFLOAD_DIFF_CHANNEL(20),
.max_sample_rate_Hz = 500 * HZ_PER_KHZ,
.tconv_ns = 1500,
};
static const struct ltc2378_chip_info ltc2378_16_chip_info = {
.name = "ltc2378-16",
.chan = LTC2378_DIFF_CHANNEL(16),
.offload_chan = LTC2378_OFFLOAD_DIFF_CHANNEL(16),
.max_sample_rate_Hz = 1 * HZ_PER_MHZ,
.tconv_ns = 527,
};
static const struct ltc2378_chip_info ltc2378_18_chip_info = {
.name = "ltc2378-18",
.chan = LTC2378_DIFF_CHANNEL(18),
.offload_chan = LTC2378_OFFLOAD_DIFF_CHANNEL(18),
.max_sample_rate_Hz = 1 * HZ_PER_MHZ,
.tconv_ns = 527,
};
static const struct ltc2378_chip_info ltc2378_20_chip_info = {
.name = "ltc2378-20",
.chan = LTC2378_DIFF_CHANNEL(20),
.offload_chan = LTC2378_OFFLOAD_DIFF_CHANNEL(20),
.max_sample_rate_Hz = 1 * HZ_PER_MHZ,
.tconv_ns = 675,
};
static const struct ltc2378_chip_info ltc2379_18_chip_info = {
.name = "ltc2379-18",
.chan = LTC2378_DIFF_CHANNEL(18),
.offload_chan = LTC2378_OFFLOAD_DIFF_CHANNEL(18),
.max_sample_rate_Hz = 1600 * HZ_PER_KHZ,
.tconv_ns = 412,
};
static const struct ltc2378_chip_info ltc2380_16_chip_info = {
.name = "ltc2380-16",
.chan = LTC2378_DIFF_CHANNEL(16),
.offload_chan = LTC2378_OFFLOAD_DIFF_CHANNEL(16),
.max_sample_rate_Hz = 2 * HZ_PER_MHZ,
.tconv_ns = 322,
};
static int ltc2378_convert_and_acquire(struct ltc2378_state *st)
@ -257,7 +374,137 @@ static int ltc2378_read_raw(struct iio_dev *indio_dev,
*val2 = chan->scan_type.realbits;
return IIO_VAL_FRACTIONAL_LOG2;
case IIO_CHAN_INFO_SAMP_FREQ:
*val = st->cnv_Hz;
return IIO_VAL_INT;
default:
return -EINVAL;
}
}
static int ltc2378_read_avail(struct iio_dev *indio_dev,
struct iio_chan_spec const *chan,
const int **vals, int *type, int *length, long mask)
{
struct ltc2378_state *st = iio_priv(indio_dev);
switch (mask) {
case IIO_CHAN_INFO_SAMP_FREQ:
*vals = st->sample_freq_range;
*type = IIO_VAL_INT;
return IIO_AVAIL_RANGE;
default:
return -EINVAL;
}
}
/*
* SPI offload wiring schema
*
* +-------------+ +-------------+
* | CNV |<-----+--| GPIO |
* | | +--| PWM0 |
* | | | |
* | | +--| PWM1 |
* | | | +-------------+
* | | +->| TRIGGER |
* | | | |
* | ADC | | SPI |
* | | | controller |
* | | | |
* | SDI |<--------| SDO |
* | SDO |-------->| SDI |
* | SCLK |<--------| SCLK |
* +-------------+ +-------------+
*
*/
static int ltc2378_update_conversion_rate(struct ltc2378_state *st, int freq_Hz)
{
struct spi_offload_trigger_config config = st->offload_trigger_config;
unsigned int min_read_offset, offload_period_ns;
struct pwm_waveform cnv_wf = { };
u64 target = LTC2378_TCNV_HIGH_NS;
unsigned int count;
u64 offload_offset_ns;
int ret;
if (freq_Hz == 0)
return -EINVAL;
if (!in_range(freq_Hz, 1, st->info->max_sample_rate_Hz))
return -ERANGE;
/* Configure CNV PWM waveform */
cnv_wf.period_length_ns = DIV_ROUND_CLOSEST(NSEC_PER_SEC, freq_Hz);
/*
* Ensure CNV high time meets minimum requirement (20ns). The PWM
* hardware may round the duty cycle, so iterate until we get at least
* the minimum required high time (or reach a try count limit).
*/
count = 100;
do {
cnv_wf.duty_length_ns = target;
ret = pwm_round_waveform_might_sleep(st->cnv_trigger, &cnv_wf);
if (ret)
return ret;
target += 10; /* Increment by PWM duty cycle period */
} while (count-- && cnv_wf.duty_length_ns < LTC2378_TCNV_HIGH_NS);
/* Check the minimum CNV high time is met */
if (cnv_wf.duty_length_ns < LTC2378_TCNV_HIGH_NS)
return -EDOM;
/*
* Configure SPI offload PWM trigger.
* The trigger should fire after tBUSYLH + tCONV + tDSDOBUSYL.
* Minimum time needed: TBUSYLH (13ns) + TCONV (part-specific) + TDSDOBUSYL (5ns)
*
* Use the same period as CNV PWM to avoid timing issues.
* Convert back from period to frequency for the SPI offload API.
*/
offload_period_ns = cnv_wf.period_length_ns;
config.periodic.frequency_hz = div_u64(HZ_PER_GHZ, offload_period_ns);
min_read_offset = LTC2378_TBUSYLH_NS + st->info->tconv_ns + LTC2378_TDSDOBUSYL_NS;
offload_offset_ns = min_read_offset;
count = 100;
do {
config.periodic.offset_ns = offload_offset_ns;
ret = spi_offload_trigger_validate(st->offload_trigger, &config);
if (ret)
return ret;
offload_offset_ns += 10;
} while (count-- && config.periodic.offset_ns < min_read_offset);
/* Check the minimum CNV to SCLK delay is met */
if (config.periodic.offset_ns < min_read_offset)
return -EDOM;
/* Check the PWM periods remain the same */
offload_period_ns = div64_u64(HZ_PER_GHZ, config.periodic.frequency_hz);
if (cnv_wf.period_length_ns != offload_period_ns)
return -EDOM;
st->offload_trigger_config = config;
st->cnv_wf = cnv_wf;
st->cnv_Hz = DIV_ROUND_CLOSEST_ULL(HZ_PER_GHZ, cnv_wf.period_length_ns);
return 0;
}
static int ltc2378_write_raw(struct iio_dev *indio_dev,
struct iio_chan_spec const *chan,
int val, int val2, long mask)
{
struct ltc2378_state *st = iio_priv(indio_dev);
IIO_DEV_ACQUIRE_DIRECT_MODE(indio_dev, claim);
if (IIO_DEV_ACQUIRE_FAILED(claim))
return -EBUSY;
switch (mask) {
case IIO_CHAN_INFO_SAMP_FREQ:
return ltc2378_update_conversion_rate(st, val);
default:
return -EINVAL;
}
@ -267,6 +514,111 @@ static const struct iio_info ltc2378_iio_info = {
.read_raw = &ltc2378_read_raw,
};
static const struct iio_info ltc2378_offload_iio_info = {
.read_raw = &ltc2378_read_raw,
.read_avail = &ltc2378_read_avail,
.write_raw = &ltc2378_write_raw,
};
static int ltc2378_offload_buffer_postenable(struct iio_dev *indio_dev)
{
struct ltc2378_state *st = iio_priv(indio_dev);
int ret;
ret = pwm_set_waveform_might_sleep(st->cnv_trigger, &st->cnv_wf, true);
if (ret)
return ret;
ret = spi_offload_trigger_enable(st->offload, st->offload_trigger,
&st->offload_trigger_config);
if (ret)
goto out_pwm_disable;
return 0;
out_pwm_disable:
pwm_disable(st->cnv_trigger);
return ret;
}
static int ltc2378_offload_buffer_predisable(struct iio_dev *indio_dev)
{
struct ltc2378_state *st = iio_priv(indio_dev);
spi_offload_trigger_disable(st->offload, st->offload_trigger);
pwm_disable(st->cnv_trigger);
return 0;
}
static const struct iio_buffer_setup_ops ltc2378_offload_buffer_ops = {
.postenable = &ltc2378_offload_buffer_postenable,
.predisable = &ltc2378_offload_buffer_predisable,
};
static int ltc2378_prepare_offload_message(struct device *dev,
struct ltc2378_state *st)
{
unsigned int resolution = st->info->offload_chan.scan_type.realbits;
st->offload_xfer.bits_per_word = resolution;
st->offload_xfer.len = spi_bpw_to_bytes(resolution);
st->offload_xfer.offload_flags = SPI_OFFLOAD_XFER_RX_STREAM;
/* Initialize message with offload */
spi_message_init_with_transfers(&st->offload_msg, &st->offload_xfer, 1);
st->offload_msg.offload = st->offload;
return devm_spi_optimize_message(dev, st->spi, &st->offload_msg);
}
static int ltc2378_spi_offload_setup(struct iio_dev *indio_dev,
struct ltc2378_state *st)
{
struct device *dev = &st->spi->dev;
struct dma_chan *rx_dma;
indio_dev->setup_ops = &ltc2378_offload_buffer_ops;
st->offload_trigger = devm_spi_offload_trigger_get(dev, st->offload,
SPI_OFFLOAD_TRIGGER_PERIODIC);
if (IS_ERR(st->offload_trigger))
return dev_err_probe(dev, PTR_ERR(st->offload_trigger),
"failed to get offload trigger\n");
st->offload_trigger_config.type = SPI_OFFLOAD_TRIGGER_PERIODIC;
rx_dma = devm_spi_offload_rx_stream_request_dma_chan(dev, st->offload);
if (IS_ERR(rx_dma))
return dev_err_probe(dev, PTR_ERR(rx_dma), "failed to get offload RX DMA\n");
return devm_iio_dmaengine_buffer_setup_with_handle(dev, indio_dev, rx_dma,
IIO_BUFFER_DIRECTION_IN);
}
static int ltc2378_pwm_get(struct ltc2378_state *st)
{
struct device *dev = &st->spi->dev;
st->cnv_trigger = devm_pwm_get(dev, NULL);
if (IS_ERR(st->cnv_trigger))
return dev_err_probe(dev, PTR_ERR(st->cnv_trigger),
"failed to get cnv pwm\n");
/*
* Disable the PWM connected to CNV in case it was left running by
* something else.
*/
pwm_disable(st->cnv_trigger);
return 0;
}
static const struct spi_offload_config ltc2378_offload_config = {
.capability_flags = SPI_OFFLOAD_CAP_TRIGGER |
SPI_OFFLOAD_CAP_RX_STREAM_DMA,
};
static int ltc2378_ref_setup(struct device *dev, struct ltc2378_state *st)
{
int ret;
@ -307,7 +659,6 @@ static int ltc2378_probe(struct spi_device *spi)
return ret;
indio_dev->name = st->info->name;
indio_dev->info = &ltc2378_iio_info;
indio_dev->modes = INDIO_DIRECT_MODE;
st->cnv_gpio = devm_gpiod_get(dev, "cnv", GPIOD_OUT_LOW);
@ -315,8 +666,53 @@ static int ltc2378_probe(struct spi_device *spi)
return dev_err_probe(dev, PTR_ERR(st->cnv_gpio),
"failed to get CNV GPIO");
indio_dev->channels = &st->info->chan;
indio_dev->num_channels = 1;
st->offload = devm_spi_offload_get(dev, spi, &ltc2378_offload_config);
ret = PTR_ERR_OR_ZERO(st->offload);
/* Fall back to low speed usage when no SPI offload is available. */
if (ret == -ENODEV) {
indio_dev->info = &ltc2378_iio_info;
indio_dev->channels = &st->info->chan;
indio_dev->num_channels = 1;
} else if (ret) {
return dev_err_probe(dev, ret, "failed to get offload\n");
} else {
indio_dev->info = &ltc2378_offload_iio_info;
indio_dev->channels = &st->info->offload_chan;
indio_dev->num_channels = 1;
ret = ltc2378_spi_offload_setup(indio_dev, st);
if (ret)
return dev_err_probe(dev, ret,
"failed to setup SPI offload\n");
ret = ltc2378_pwm_get(st);
if (ret)
return dev_err_probe(dev, ret, "failed to get PWM\n");
st->sample_freq_range[0] = 1; /* min */
st->sample_freq_range[1] = 1; /* step */
st->sample_freq_range[2] = st->info->max_sample_rate_Hz; /* max */
/*
* Start with a slower sampling rate so there is some room for
* adjusting the sample averaging and the sampling frequency
* without hitting the maximum conversion rate.
*/
ret = ltc2378_update_conversion_rate(st, st->info->max_sample_rate_Hz >> 4);
if (ret)
return dev_err_probe(dev, ret,
"failed to set offload samp freq\n");
ret = ltc2378_prepare_offload_message(&spi->dev, st);
if (ret)
return dev_err_probe(dev, ret, "failed to optimize SPI message\n");
/*
* Set single-read transfer bits_per_word so the SPI subsystem
* rearranges data to CPU endianness, enabling us to reuse
* offload_chan specifications for single-shot reads.
*/
st->xfer.bits_per_word = st->info->offload_chan.scan_type.realbits;
}
st->xfer.rx_buf = &st->scan.data;
st->xfer.len = spi_bpw_to_bytes(indio_dev->channels[0].scan_type.realbits);
@ -385,3 +781,5 @@ module_spi_driver(ltc2378_driver);
MODULE_AUTHOR("Marcelo Schmitt <marcelo.schmitt@analog.com>");
MODULE_DESCRIPTION("Analog Devices LTC2378 ADC series driver");
MODULE_LICENSE("GPL");
MODULE_IMPORT_NS("IIO_DMAENGINE_BUFFER");
MODULE_IMPORT_NS("SPI_OFFLOAD");