iio: adc: ad7944: add support for SPI offload

Add support for SPI offload to the ad7944 driver. This allows reading
data at the max sample rate of 2.5 MSPS.

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Nuno Sa <nuno.sa@analog.com>
Signed-off-by: David Lechner <dlechner@baylibre.com>
Link: https://patch.msgid.link/20250207-dlech-mainline-spi-engine-offload-2-v8-11-e48a489be48c@baylibre.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

2 files changed, 277 insertions, 16 deletions

diff --git a/drivers/iio/adc/Kconfig b/drivers/iio/adc/Kconfig
index a3e8ac569ce4..1555920f473b 100644
--- a/drivers/iio/adc/Kconfig
+++ b/drivers/iio/adc/Kconfig
@@ -360,7 +360,9 @@ config AD7923
 config AD7944
 	tristate "Analog Devices AD7944 and similar ADCs driver"
 	depends on SPI
+	select SPI_OFFLOAD
 	select IIO_BUFFER
+	select IIO_BUFFER_DMAENGINE
 	select IIO_TRIGGERED_BUFFER
 	help
 	  Say yes here to build support for Analog Devices
diff --git a/drivers/iio/adc/ad7944.c b/drivers/iio/adc/ad7944.c
index abfababcea10..9a7825ea5087 100644
--- a/drivers/iio/adc/ad7944.c
+++ b/drivers/iio/adc/ad7944.c
@@ -16,11 +16,14 @@
 #include <linux/module.h>
 #include <linux/property.h>
 #include <linux/regulator/consumer.h>
+#include <linux/spi/offload/consumer.h>
 #include <linux/spi/spi.h>
 #include <linux/string_helpers.h>
+#include <linux/units.h>
 
 #include <linux/iio/iio.h>
 #include <linux/iio/sysfs.h>
+#include <linux/iio/buffer-dmaengine.h>
 #include <linux/iio/trigger_consumer.h>
 #include <linux/iio/triggered_buffer.h>
 
@@ -54,6 +57,12 @@ struct ad7944_adc {
 	enum ad7944_spi_mode spi_mode;
 	struct spi_transfer xfers[3];
 	struct spi_message msg;
+	struct spi_transfer offload_xfers[2];
+	struct spi_message offload_msg;
+	struct spi_offload *offload;
+	struct spi_offload_trigger *offload_trigger;
+	unsigned long offload_trigger_hz;
+	int sample_freq_range[3];
 	void *chain_mode_buf;
 	/* Chip-specific timing specifications. */
 	const struct ad7944_timing_spec *timing_spec;
@@ -81,6 +90,8 @@ struct ad7944_adc {
 
 /* quite time before CNV rising edge */
 #define AD7944_T_QUIET_NS	20
+/* minimum CNV high time to trigger conversion */
+#define AD7944_T_CNVH_NS	10
 
 static const struct ad7944_timing_spec ad7944_timing_spec = {
 	.conv_ns = 420,
@@ -95,7 +106,9 @@ static const struct ad7944_timing_spec ad7986_timing_spec = {
 struct ad7944_chip_info {
 	const char *name;
 	const struct ad7944_timing_spec *timing_spec;
+	u32 max_sample_rate_hz;
 	const struct iio_chan_spec channels[2];
+	const struct iio_chan_spec offload_channels[1];
 };
 
 /* get number of bytes for SPI xfer */
@@ -105,13 +118,15 @@ struct ad7944_chip_info {
  * AD7944_DEFINE_CHIP_INFO - Define a chip info structure for a specific chip
  * @_name: The name of the chip
  * @_ts: The timing specification for the chip
+ * @_max: The maximum sample rate in Hz
  * @_bits: The number of bits in the conversion result
  * @_diff: Whether the chip is true differential or not
  */
-#define AD7944_DEFINE_CHIP_INFO(_name, _ts, _bits, _diff)		\
+#define AD7944_DEFINE_CHIP_INFO(_name, _ts, _max, _bits, _diff)		\
 static const struct ad7944_chip_info _name##_chip_info = {		\
 	.name = #_name,							\
 	.timing_spec = &_ts##_timing_spec,				\
+	.max_sample_rate_hz = _max,					\
 	.channels = {							\
 		{							\
 			.type = IIO_VOLTAGE,				\
@@ -129,13 +144,43 @@ static const struct ad7944_chip_info _name##_chip_info = {		\
 		},							\
 		IIO_CHAN_SOFT_TIMESTAMP(1),				\
 	},								\
+	.offload_channels = {						\
+		{							\
+			.type = IIO_VOLTAGE,				\
+			.indexed = 1,					\
+			.differential = _diff,				\
+			.channel = 0,					\
+			.channel2 = _diff ? 1 : 0,			\
+			.scan_index = 0,				\
+			.scan_type.sign = _diff ? 's' : 'u',		\
+			.scan_type.realbits = _bits,			\
+			.scan_type.storagebits = 32,			\
+			.scan_type.endianness = IIO_CPU,		\
+			.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),		\
+		},							\
+	},								\
 }
 
+/*
+ * Notes on the offload channels:
+ * - There is no soft timestamp since everything is done in hardware.
+ * - There is a sampling frequency attribute added. This controls the SPI
+ *   offload trigger.
+ * - The storagebits value depends on the SPI offload provider. Currently there
+ *   is only one supported provider, namely the ADI PULSAR ADC HDL project,
+ *   which always uses 32-bit words for data values, even for <= 16-bit ADCs.
+ *   So the value is just hardcoded to 32 for now.
+ */
+
 /* pseudo-differential with ground sense */
-AD7944_DEFINE_CHIP_INFO(ad7944, ad7944, 14, 0);
-AD7944_DEFINE_CHIP_INFO(ad7985, ad7944, 16, 0);
+AD7944_DEFINE_CHIP_INFO(ad7944, ad7944, 2.5 * MEGA, 14, 0);
+AD7944_DEFINE_CHIP_INFO(ad7985, ad7944, 2.5 * MEGA, 16, 0);
 /* fully differential */
-AD7944_DEFINE_CHIP_INFO(ad7986, ad7986, 18, 1);
+AD7944_DEFINE_CHIP_INFO(ad7986, ad7986, 2 * MEGA, 18, 1);
 
 static int ad7944_3wire_cs_mode_init_msg(struct device *dev, struct ad7944_adc *adc,
 					 const struct iio_chan_spec *chan)
@@ -239,6 +284,48 @@ static int ad7944_chain_mode_init_msg(struct device *dev, struct ad7944_adc *adc
 	return devm_spi_optimize_message(dev, adc->spi, &adc->msg);
 }
 
+/*
+ * Unlike ad7944_3wire_cs_mode_init_msg(), this creates a message that reads
+ * during the conversion phase instead of the acquisition phase when reading
+ * a sample from the ADC. This is needed to be able to read at the maximum
+ * sample rate. It requires the SPI controller to have offload support and a
+ * high enough SCLK rate to read the sample during the conversion phase.
+ */
+static int ad7944_3wire_cs_mode_init_offload_msg(struct device *dev,
+						 struct ad7944_adc *adc,
+						 const struct iio_chan_spec *chan)
+{
+	struct spi_transfer *xfers = adc->offload_xfers;
+	int ret;
+
+	/*
+	 * CS is tied to CNV and we need a low to high transition to start the
+	 * conversion, so place CNV low for t_QUIET to prepare for this.
+	 */
+	xfers[0].delay.value = AD7944_T_QUIET_NS;
+	xfers[0].delay.unit = SPI_DELAY_UNIT_NSECS;
+	/* CNV has to be high for a minimum time to trigger conversion. */
+	xfers[0].cs_change = 1;
+	xfers[0].cs_change_delay.value = AD7944_T_CNVH_NS;
+	xfers[0].cs_change_delay.unit = SPI_DELAY_UNIT_NSECS;
+
+	/* Then we can read the previous sample during the conversion phase */
+	xfers[1].offload_flags = SPI_OFFLOAD_XFER_RX_STREAM;
+	xfers[1].len = AD7944_SPI_BYTES(chan->scan_type);
+	xfers[1].bits_per_word = chan->scan_type.realbits;
+
+	spi_message_init_with_transfers(&adc->offload_msg, xfers,
+					ARRAY_SIZE(adc->offload_xfers));
+
+	adc->offload_msg.offload = adc->offload;
+
+	ret = devm_spi_optimize_message(dev, adc->spi, &adc->offload_msg);
+	if (ret)
+		return dev_err_probe(dev, ret, "failed to prepare offload msg\n");
+
+	return 0;
+}
+
 /**
  * ad7944_convert_and_acquire - Perform a single conversion and acquisition
  * @adc: The ADC device structure
@@ -294,6 +381,23 @@ static int ad7944_single_conversion(struct ad7944_adc *adc,
 	return IIO_VAL_INT;
 }
 
+static int ad7944_read_avail(struct iio_dev *indio_dev,
+			     struct iio_chan_spec const *chan,
+			     const int **vals, int *type, int *length,
+			     long mask)
+{
+	struct ad7944_adc *adc = iio_priv(indio_dev);
+
+	switch (mask) {
+	case IIO_CHAN_INFO_SAMP_FREQ:
+		*vals = adc->sample_freq_range;
+		*type = IIO_VAL_INT;
+		return IIO_AVAIL_RANGE;
+	default:
+		return -EINVAL;
+	}
+}
+
 static int ad7944_read_raw(struct iio_dev *indio_dev,
 			   const struct iio_chan_spec *chan,
 			   int *val, int *val2, long info)
@@ -326,13 +430,104 @@ static int ad7944_read_raw(struct iio_dev *indio_dev,
 			return -EINVAL;
 		}
 
+	case IIO_CHAN_INFO_SAMP_FREQ:
+		*val = adc->offload_trigger_hz;
+		return IIO_VAL_INT;
+
+	default:
+		return -EINVAL;
+	}
+}
+
+static int ad7944_set_sample_freq(struct ad7944_adc *adc, int val)
+{
+	struct spi_offload_trigger_config config = {
+		.type = SPI_OFFLOAD_TRIGGER_PERIODIC,
+		.periodic = {
+			.frequency_hz = val,
+		},
+	};
+	int ret;
+
+	ret = spi_offload_trigger_validate(adc->offload_trigger, &config);
+	if (ret)
+		return ret;
+
+	adc->offload_trigger_hz = config.periodic.frequency_hz;
+
+	return 0;
+}
+
+static int ad7944_write_raw(struct iio_dev *indio_dev,
+			    const struct iio_chan_spec *chan,
+			    int val, int val2, long info)
+{
+	struct ad7944_adc *adc = iio_priv(indio_dev);
+
+	switch (info) {
+	case IIO_CHAN_INFO_SAMP_FREQ:
+		if (val < 1 || val > adc->sample_freq_range[2])
+			return -EINVAL;
+
+		return ad7944_set_sample_freq(adc, val);
 	default:
 		return -EINVAL;
 	}
 }
 
+static int ad7944_write_raw_get_fmt(struct iio_dev *indio_dev,
+				    const struct iio_chan_spec *chan,
+				    long mask)
+{
+	switch (mask) {
+	case IIO_CHAN_INFO_SAMP_FREQ:
+		return IIO_VAL_INT;
+	default:
+		return IIO_VAL_INT_PLUS_MICRO;
+	}
+}
+
 static const struct iio_info ad7944_iio_info = {
+	.read_avail = &ad7944_read_avail,
 	.read_raw = &ad7944_read_raw,
+	.write_raw = &ad7944_write_raw,
+	.write_raw_get_fmt = &ad7944_write_raw_get_fmt,
+};
+
+static int ad7944_offload_buffer_postenable(struct iio_dev *indio_dev)
+{
+	struct ad7944_adc *adc = iio_priv(indio_dev);
+	struct spi_offload_trigger_config config = {
+		.type = SPI_OFFLOAD_TRIGGER_PERIODIC,
+		.periodic = {
+			.frequency_hz = adc->offload_trigger_hz,
+		},
+	};
+	int ret;
+
+	gpiod_set_value_cansleep(adc->turbo, 1);
+
+	ret = spi_offload_trigger_enable(adc->offload, adc->offload_trigger,
+					 &config);
+	if (ret)
+		gpiod_set_value_cansleep(adc->turbo, 0);
+
+	return ret;
+}
+
+static int ad7944_offload_buffer_predisable(struct iio_dev *indio_dev)
+{
+	struct ad7944_adc *adc = iio_priv(indio_dev);
+
+	spi_offload_trigger_disable(adc->offload, adc->offload_trigger);
+	gpiod_set_value_cansleep(adc->turbo, 0);
+
+	return 0;
+}
+
+static const struct iio_buffer_setup_ops ad7944_offload_buffer_setup_ops = {
+	.postenable = &ad7944_offload_buffer_postenable,
+	.predisable = &ad7944_offload_buffer_predisable,
 };
 
 static irqreturn_t ad7944_trigger_handler(int irq, void *p)
@@ -446,6 +641,11 @@ static const char * const ad7944_power_supplies[] = {
 	"avdd",	"dvdd",	"bvdd", "vio"
 };
 
+static const struct spi_offload_config ad7944_offload_config = {
+	.capability_flags = SPI_OFFLOAD_CAP_TRIGGER |
+			    SPI_OFFLOAD_CAP_RX_STREAM_DMA,
+};
+
 static int ad7944_probe(struct spi_device *spi)
 {
 	const struct ad7944_chip_info *chip_info;
@@ -471,6 +671,10 @@ static int ad7944_probe(struct spi_device *spi)
 
 	adc->timing_spec = chip_info->timing_spec;
 
+	adc->sample_freq_range[0] = 1; /* min */
+	adc->sample_freq_range[1] = 1; /* step */
+	adc->sample_freq_range[2] = chip_info->max_sample_rate_hz; /* max */
+
 	ret = device_property_match_property_string(dev, "adi,spi-mode",
 						    ad7944_spi_modes,
 						    ARRAY_SIZE(ad7944_spi_modes));
@@ -590,20 +794,74 @@ static int ad7944_probe(struct spi_device *spi)
 	indio_dev->modes = INDIO_DIRECT_MODE;
 	indio_dev->info = &ad7944_iio_info;
 
-	if (adc->spi_mode == AD7944_SPI_MODE_CHAIN) {
-		indio_dev->available_scan_masks = chain_scan_masks;
-		indio_dev->channels = chain_chan;
-		indio_dev->num_channels = n_chain_dev + 1;
+	adc->offload = devm_spi_offload_get(dev, spi, &ad7944_offload_config);
+	ret = PTR_ERR_OR_ZERO(adc->offload);
+	if (ret && ret != -ENODEV)
+		return dev_err_probe(dev, ret, "failed to get offload\n");
+
+	/* Fall back to low speed usage when no SPI offload available. */
+	if (ret == -ENODEV) {
+		if (adc->spi_mode == AD7944_SPI_MODE_CHAIN) {
+			indio_dev->available_scan_masks = chain_scan_masks;
+			indio_dev->channels = chain_chan;
+			indio_dev->num_channels = n_chain_dev + 1;
+		} else {
+			indio_dev->channels = chip_info->channels;
+			indio_dev->num_channels = ARRAY_SIZE(chip_info->channels);
+		}
+
+		ret = devm_iio_triggered_buffer_setup(dev, indio_dev,
+						      iio_pollfunc_store_time,
+						      ad7944_trigger_handler,
+						      NULL);
+		if (ret)
+			return ret;
 	} else {
-		indio_dev->channels = chip_info->channels;
-		indio_dev->num_channels = ARRAY_SIZE(chip_info->channels);
-	}
+		struct dma_chan *rx_dma;
 
-	ret = devm_iio_triggered_buffer_setup(dev, indio_dev,
-					      iio_pollfunc_store_time,
-					      ad7944_trigger_handler, NULL);
-	if (ret)
-		return ret;
+		if (adc->spi_mode != AD7944_SPI_MODE_SINGLE)
+			return dev_err_probe(dev, -EINVAL,
+				"offload only supported in single mode\n");
+
+		indio_dev->setup_ops = &ad7944_offload_buffer_setup_ops;
+		indio_dev->channels = chip_info->offload_channels;
+		indio_dev->num_channels = ARRAY_SIZE(chip_info->offload_channels);
+
+		adc->offload_trigger = devm_spi_offload_trigger_get(dev,
+			adc->offload, SPI_OFFLOAD_TRIGGER_PERIODIC);
+		if (IS_ERR(adc->offload_trigger))
+			return dev_err_probe(dev, PTR_ERR(adc->offload_trigger),
+					     "failed to get offload trigger\n");
+
+		ret = ad7944_set_sample_freq(adc, 2 * MEGA);
+		if (ret)
+			return dev_err_probe(dev, ret,
+					     "failed to init sample rate\n");
+
+		rx_dma = devm_spi_offload_rx_stream_request_dma_chan(dev,
+								     adc->offload);
+		if (IS_ERR(rx_dma))
+			return dev_err_probe(dev, PTR_ERR(rx_dma),
+					     "failed to get offload RX DMA\n");
+
+		/*
+		 * REVISIT: ideally, we would confirm that the offload RX DMA
+		 * buffer layout is the same as what is hard-coded in
+		 * offload_channels. Right now, the only supported offload
+		 * is the pulsar_adc project which always uses 32-bit word
+		 * size for data values, regardless of the SPI bits per word.
+		 */
+
+		ret = devm_iio_dmaengine_buffer_setup_with_handle(dev,
+			indio_dev, rx_dma, IIO_BUFFER_DIRECTION_IN);
+		if (ret)
+			return ret;
+
+		ret = ad7944_3wire_cs_mode_init_offload_msg(dev, adc,
+			&chip_info->offload_channels[0]);
+		if (ret)
+			return ret;
+	}
 
 	return devm_iio_device_register(dev, indio_dev);
 }
@@ -638,3 +896,4 @@ module_spi_driver(ad7944_driver);
 MODULE_AUTHOR("David Lechner <dlechner@baylibre.com>");
 MODULE_DESCRIPTION("Analog Devices AD7944 PulSAR ADC family driver");
 MODULE_LICENSE("GPL");
+MODULE_IMPORT_NS("IIO_DMAENGINE_BUFFER");