[PATCH v3 0/2] iio: ad7380: add SPI offload support

[PATCH v3 0/2] iio: ad7380: add SPI offload support

[Angelo Dureghello]

Add SPI offload support for the ad7380 ADC. 

Signed-off-by: Angelo Dureghello <adureghello@baylibre.com>
---
Changes in v2:
- fix return value on offload probe,
- add documentation patch 2/2.

Changes in v3:
- fix tabs erroneously added,
- fix documentation syntax error,
- add a note for the 4 channels ADC variants.
- Link to v2: https://lore.kernel.org/r/20250304-wip-bl-spi-offload-ad7380-v2-0-0fef61f2650a@baylibre.com

---
Angelo Dureghello (2):
      iio: ad7380: add support for SPI offload
      docs: iio: ad7380: add SPI offload support

 Documentation/iio/ad7380.rst |  36 +++
 drivers/iio/adc/Kconfig      |   2 +
 drivers/iio/adc/ad7380.c     | 509 ++++++++++++++++++++++++++++++++++++++++---
 3 files changed, 511 insertions(+), 36 deletions(-)
---
base-commit: b7508a5a672275694c2a1b09a5f491ca2a56bbcf
change-id: 20250304-wip-bl-spi-offload-ad7380-ad675f2a2f5c

Best regards,
-- 
Angelo Dureghello <adureghello@baylibre.com>

[PATCH v3 1/2] iio: ad7380: add support for SPI offload

[Angelo Dureghello]

Add support for SPI offload to the ad7380 driver. SPI offload allows
sampling data at the max sample rate (2MSPS with one SDO line).

This is developed and tested against the ADI example FPGA design for
this family of ADCs [1].

[1]: http://analogdevicesinc.github.io/hdl/projects/ad738x_fmc/index.html

Signed-off-by: Angelo Dureghello <adureghello@baylibre.com>
---
 drivers/iio/adc/Kconfig  |   2 +
 drivers/iio/adc/ad7380.c | 509 +++++++++++++++++++++++++++++++++++++++++++----
 2 files changed, 475 insertions(+), 36 deletions(-)

diff --git a/drivers/iio/adc/Kconfig b/drivers/iio/adc/Kconfig
index 27413516216cb3f83cf1d995b9ffc22bf01776a4..c528f4632c0ef6782269d8afa89c17d2046d28a3 100644
--- a/drivers/iio/adc/Kconfig
+++ b/drivers/iio/adc/Kconfig
@@ -218,7 +218,9 @@ config AD7298
 config AD7380
 	tristate "Analog Devices AD7380 ADC driver"
 	depends on SPI_MASTER
+	select SPI_OFFLOAD
 	select IIO_BUFFER
+	select IIO_BUFFER_DMAENGINE
 	select IIO_TRIGGER
 	select IIO_TRIGGERED_BUFFER
 	help
diff --git a/drivers/iio/adc/ad7380.c b/drivers/iio/adc/ad7380.c
index f232ad1a49634baeedc655916bc7a967604a1206..39a5e55fa7e8a6706e15750d07fa4b0fda7175eb 100644
--- a/drivers/iio/adc/ad7380.c
+++ b/drivers/iio/adc/ad7380.c
@@ -15,6 +15,9 @@
  * ad7386/7/8-4 : https://www.analog.com/media/en/technical-documentation/data-sheets/ad7386-4-7387-4-7388-4.pdf
  * adaq4370-4 : https://www.analog.com/media/en/technical-documentation/data-sheets/adaq4370-4.pdf
  * adaq4380-4 : https://www.analog.com/media/en/technical-documentation/data-sheets/adaq4380-4.pdf
+ *
+ * HDL ad738x_fmc: https://analogdevicesinc.github.io/hdl/projects/ad738x_fmc/index.html
+ *
  */
 
 #include <linux/align.h>
@@ -29,11 +32,13 @@
 #include <linux/regmap.h>
 #include <linux/regulator/consumer.h>
 #include <linux/slab.h>
+#include <linux/spi/offload/consumer.h>
 #include <linux/spi/spi.h>
 #include <linux/units.h>
 #include <linux/util_macros.h>
 
 #include <linux/iio/buffer.h>
+#include <linux/iio/buffer-dmaengine.h>
 #include <linux/iio/events.h>
 #include <linux/iio/iio.h>
 #include <linux/iio/trigger_consumer.h>
@@ -92,6 +97,12 @@
 #define AD7380_NUM_SDO_LINES		1
 #define AD7380_DEFAULT_GAIN_MILLI	1000
 
+/*
+ * Using SPI offload, storagebits is always 32, so can't be used to compute struct
+ * spi_transfer.len. Using realbits instead.
+ */
+#define AD7380_SPI_BYTES(scan_type)	((scan_type)->realbits > 16 ? 4 : 2)
+
 struct ad7380_timing_specs {
 	const unsigned int t_csh_ns;	/* CS minimum high time */
 };
@@ -99,6 +110,7 @@ struct ad7380_timing_specs {
 struct ad7380_chip_info {
 	const char *name;
 	const struct iio_chan_spec *channels;
+	const struct iio_chan_spec *offload_channels;
 	unsigned int num_channels;
 	unsigned int num_simult_channels;
 	bool has_hardware_gain;
@@ -111,6 +123,7 @@ struct ad7380_chip_info {
 	unsigned int num_vcm_supplies;
 	const unsigned long *available_scan_masks;
 	const struct ad7380_timing_specs *timing_specs;
+	u32 max_conversion_rate_hz;
 };
 
 static const struct iio_event_spec ad7380_events[] = {
@@ -216,6 +229,91 @@ static const struct iio_scan_type ad7380_scan_type_16_u[] = {
 	},
 };
 
+/*
+ * Defining here scan types for offload mode, since with current available HDL
+ * only a value of 32 for storagebits is supported.
+ */
+
+/* Extended scan types for 12-bit unsigned chips, offload support. */
+static const struct iio_scan_type ad7380_scan_type_12_u_offload[] = {
+	[AD7380_SCAN_TYPE_NORMAL] = {
+		.sign = 'u',
+		.realbits = 12,
+		.storagebits = 32,
+		.endianness = IIO_CPU,
+	},
+	[AD7380_SCAN_TYPE_RESOLUTION_BOOST] = {
+		.sign = 'u',
+		.realbits = 14,
+		.storagebits = 32,
+		.endianness = IIO_CPU,
+	},
+};
+
+/* Extended scan types for 14-bit signed chips, offload support. */
+static const struct iio_scan_type ad7380_scan_type_14_s_offload[] = {
+	[AD7380_SCAN_TYPE_NORMAL] = {
+		.sign = 's',
+		.realbits = 14,
+		.storagebits = 32,
+		.endianness = IIO_CPU,
+	},
+	[AD7380_SCAN_TYPE_RESOLUTION_BOOST] = {
+		.sign = 's',
+		.realbits = 16,
+		.storagebits = 32,
+		.endianness = IIO_CPU,
+	},
+};
+
+/* Extended scan types for 14-bit unsigned chips, offload support. */
+static const struct iio_scan_type ad7380_scan_type_14_u_offload[] = {
+	[AD7380_SCAN_TYPE_NORMAL] = {
+		.sign = 'u',
+		.realbits = 14,
+		.storagebits = 32,
+		.endianness = IIO_CPU,
+	},
+	[AD7380_SCAN_TYPE_RESOLUTION_BOOST] = {
+		.sign = 'u',
+		.realbits = 16,
+		.storagebits = 32,
+		.endianness = IIO_CPU,
+	},
+};
+
+/* Extended scan types for 16-bit signed_chips, offload support. */
+static const struct iio_scan_type ad7380_scan_type_16_s_offload[] = {
+	[AD7380_SCAN_TYPE_NORMAL] = {
+		.sign = 's',
+		.realbits = 16,
+		.storagebits = 32,
+		.endianness = IIO_CPU,
+	},
+	[AD7380_SCAN_TYPE_RESOLUTION_BOOST] = {
+		.sign = 's',
+		.realbits = 18,
+		.storagebits = 32,
+		.endianness = IIO_CPU,
+	},
+};
+
+/* Extended scan types for 16-bit unsigned chips, offload support. */
+static const struct iio_scan_type ad7380_scan_type_16_u_offload[] = {
+	[AD7380_SCAN_TYPE_NORMAL] = {
+		.sign = 'u',
+		.realbits = 16,
+		.storagebits = 32,
+		.endianness = IIO_CPU,
+	},
+	[AD7380_SCAN_TYPE_RESOLUTION_BOOST] = {
+		.sign = 'u',
+		.realbits = 18,
+		.storagebits = 32,
+		.endianness = IIO_CPU,
+	},
+};
+
 #define _AD7380_CHANNEL(index, bits, diff, sign, gain) {			\
 	.type = IIO_VOLTAGE,							\
 	.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |				\
@@ -237,48 +335,123 @@ static const struct iio_scan_type ad7380_scan_type_16_u[] = {
 	.num_event_specs = ARRAY_SIZE(ad7380_events),				\
 }
 
+#define _AD7380_OFFLOAD_CHANNEL(index, bits, diff, sign, gain) {		\
+	.type = IIO_VOLTAGE,							\
+	.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |                          \
+		((gain) ? BIT(IIO_CHAN_INFO_SCALE) : 0) |			\
+		((diff) ? 0 : BIT(IIO_CHAN_INFO_OFFSET)),			\
+	.info_mask_shared_by_type = ((gain) ? 0 : BIT(IIO_CHAN_INFO_SCALE)) |   \
+		BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO) |				\
+		BIT(IIO_CHAN_INFO_SAMP_FREQ),					\
+	.info_mask_shared_by_type_available =					\
+		BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO) |				\
+		BIT(IIO_CHAN_INFO_SAMP_FREQ),					\
+	.indexed = 1,                                                           \
+	.differential = (diff),                                                 \
+	.channel = (diff) ? (2 * (index)) : (index),                            \
+	.channel2 = (diff) ? (2 * (index) + 1) : 0,                             \
+	.scan_index = (index),                                                  \
+	.has_ext_scan_type = 1,                                                 \
+	.ext_scan_type = ad7380_scan_type_##bits##_##sign##_offload,            \
+	.num_ext_scan_type =                                                    \
+		ARRAY_SIZE(ad7380_scan_type_##bits##_##sign##_offload),		\
+	.event_spec = ad7380_events,                                            \
+	.num_event_specs = ARRAY_SIZE(ad7380_events),                           \
+}
+
+/*
+ * 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.
+ */
+
 #define AD7380_CHANNEL(index, bits, diff, sign)		\
 	_AD7380_CHANNEL(index, bits, diff, sign, false)
 
 #define ADAQ4380_CHANNEL(index, bits, diff, sign)	\
 	_AD7380_CHANNEL(index, bits, diff, sign, true)
 
-#define DEFINE_AD7380_2_CHANNEL(name, bits, diff, sign)	\
+#define DEFINE_AD7380_2_CHANNEL(name, bits, diff, sign) \
+static const struct iio_chan_spec name[] = {	\
+	AD7380_CHANNEL(0, bits, diff, sign),	\
+	AD7380_CHANNEL(1, bits, diff, sign),	\
+	IIO_CHAN_SOFT_TIMESTAMP(2),		\
+}
+
+#define DEFINE_AD7380_4_CHANNEL(name, bits, diff, sign) \
+static const struct iio_chan_spec name[] = {	\
+	 AD7380_CHANNEL(0, bits, diff, sign),	\
+	 AD7380_CHANNEL(1, bits, diff, sign),	\
+	 AD7380_CHANNEL(2, bits, diff, sign),	\
+	 AD7380_CHANNEL(3, bits, diff, sign),	\
+	 IIO_CHAN_SOFT_TIMESTAMP(4),		\
+}
+
+#define DEFINE_ADAQ4380_4_CHANNEL(name, bits, diff, sign) \
+static const struct iio_chan_spec name[] = {	\
+	 ADAQ4380_CHANNEL(0, bits, diff, sign),	\
+	 ADAQ4380_CHANNEL(1, bits, diff, sign),	\
+	 ADAQ4380_CHANNEL(2, bits, diff, sign),	\
+	 ADAQ4380_CHANNEL(3, bits, diff, sign),	\
+	 IIO_CHAN_SOFT_TIMESTAMP(4),		\
+}
+
+#define DEFINE_AD7380_8_CHANNEL(name, bits, diff, sign) \
+static const struct iio_chan_spec name[] = {	\
+	 AD7380_CHANNEL(0, bits, diff, sign),	\
+	 AD7380_CHANNEL(1, bits, diff, sign),	\
+	 AD7380_CHANNEL(2, bits, diff, sign),	\
+	 AD7380_CHANNEL(3, bits, diff, sign),	\
+	 AD7380_CHANNEL(4, bits, diff, sign),	\
+	 AD7380_CHANNEL(5, bits, diff, sign),	\
+	 AD7380_CHANNEL(6, bits, diff, sign),	\
+	 AD7380_CHANNEL(7, bits, diff, sign),	\
+	 IIO_CHAN_SOFT_TIMESTAMP(8),		\
+}
+
+#define AD7380_OFFLOAD_CHANNEL(index, bits, diff, sign) \
+_AD7380_OFFLOAD_CHANNEL(index, bits, diff, sign, false)
+
+#define ADAQ4380_OFFLOAD_CHANNEL(index, bits, diff, sign) \
+_AD7380_OFFLOAD_CHANNEL(index, bits, diff, sign, true)
+
+#define DEFINE_AD7380_2_OFFLOAD_CHANNEL(name, bits, diff, sign) \
 static const struct iio_chan_spec name[] = {		\
-	AD7380_CHANNEL(0, bits, diff, sign),		\
-	AD7380_CHANNEL(1, bits, diff, sign),		\
-	IIO_CHAN_SOFT_TIMESTAMP(2),			\
+	AD7380_OFFLOAD_CHANNEL(0, bits, diff, sign),	\
+	AD7380_OFFLOAD_CHANNEL(1, bits, diff, sign),	\
 }
 
-#define DEFINE_AD7380_4_CHANNEL(name, bits, diff, sign)	\
+#define DEFINE_AD7380_4_OFFLOAD_CHANNEL(name, bits, diff, sign) \
 static const struct iio_chan_spec name[] = {		\
-	AD7380_CHANNEL(0, bits, diff, sign),		\
-	AD7380_CHANNEL(1, bits, diff, sign),		\
-	AD7380_CHANNEL(2, bits, diff, sign),		\
-	AD7380_CHANNEL(3, bits, diff, sign),		\
-	IIO_CHAN_SOFT_TIMESTAMP(4),			\
+	AD7380_OFFLOAD_CHANNEL(0, bits, diff, sign),	\
+	AD7380_OFFLOAD_CHANNEL(1, bits, diff, sign),	\
+	AD7380_OFFLOAD_CHANNEL(2, bits, diff, sign),	\
+	AD7380_OFFLOAD_CHANNEL(3, bits, diff, sign),	\
 }
 
-#define DEFINE_ADAQ4380_4_CHANNEL(name, bits, diff, sign)	\
-static const struct iio_chan_spec name[] = {			\
-	ADAQ4380_CHANNEL(0, bits, diff, sign),			\
-	ADAQ4380_CHANNEL(1, bits, diff, sign),			\
-	ADAQ4380_CHANNEL(2, bits, diff, sign),			\
-	ADAQ4380_CHANNEL(3, bits, diff, sign),			\
-	IIO_CHAN_SOFT_TIMESTAMP(4),				\
+#define DEFINE_ADAQ4380_4_OFFLOAD_CHANNEL(name, bits, diff, sign) \
+static const struct iio_chan_spec name[] = {		\
+	AD7380_OFFLOAD_CHANNEL(0, bits, diff, sign),	\
+	AD7380_OFFLOAD_CHANNEL(1, bits, diff, sign),	\
+	AD7380_OFFLOAD_CHANNEL(2, bits, diff, sign),	\
+	AD7380_OFFLOAD_CHANNEL(3, bits, diff, sign),	\
 }
 
-#define DEFINE_AD7380_8_CHANNEL(name, bits, diff, sign)	\
+#define DEFINE_AD7380_8_OFFLOAD_CHANNEL(name, bits, diff, sign) \
 static const struct iio_chan_spec name[] = {		\
-	AD7380_CHANNEL(0, bits, diff, sign),		\
-	AD7380_CHANNEL(1, bits, diff, sign),		\
-	AD7380_CHANNEL(2, bits, diff, sign),		\
-	AD7380_CHANNEL(3, bits, diff, sign),		\
-	AD7380_CHANNEL(4, bits, diff, sign),		\
-	AD7380_CHANNEL(5, bits, diff, sign),		\
-	AD7380_CHANNEL(6, bits, diff, sign),		\
-	AD7380_CHANNEL(7, bits, diff, sign),		\
-	IIO_CHAN_SOFT_TIMESTAMP(8),			\
+	AD7380_OFFLOAD_CHANNEL(0, bits, diff, sign),	\
+	AD7380_OFFLOAD_CHANNEL(1, bits, diff, sign),	\
+	AD7380_OFFLOAD_CHANNEL(2, bits, diff, sign),	\
+	AD7380_OFFLOAD_CHANNEL(3, bits, diff, sign),	\
+	AD7380_OFFLOAD_CHANNEL(4, bits, diff, sign),	\
+	AD7380_OFFLOAD_CHANNEL(5, bits, diff, sign),	\
+	AD7380_OFFLOAD_CHANNEL(6, bits, diff, sign),	\
+	AD7380_OFFLOAD_CHANNEL(7, bits, diff, sign),	\
 }
 
 /* fully differential */
@@ -301,6 +474,27 @@ DEFINE_AD7380_8_CHANNEL(ad7386_4_channels, 16, 0, u);
 DEFINE_AD7380_8_CHANNEL(ad7387_4_channels, 14, 0, u);
 DEFINE_AD7380_8_CHANNEL(ad7388_4_channels, 12, 0, u);
 
+/* offload channels */
+DEFINE_AD7380_2_OFFLOAD_CHANNEL(ad7380_offload_channels, 16, 1, s);
+DEFINE_AD7380_2_OFFLOAD_CHANNEL(ad7381_offload_channels, 14, 1, s);
+DEFINE_AD7380_4_OFFLOAD_CHANNEL(ad7380_4_offload_channels, 16, 1, s);
+DEFINE_AD7380_4_OFFLOAD_CHANNEL(ad7381_4_offload_channels, 14, 1, s);
+DEFINE_ADAQ4380_4_OFFLOAD_CHANNEL(adaq4380_4_offload_channels, 16, 1, s);
+
+/* pseudo differential */
+DEFINE_AD7380_2_OFFLOAD_CHANNEL(ad7383_offload_channels, 16, 0, s);
+DEFINE_AD7380_2_OFFLOAD_CHANNEL(ad7384_offload_channels, 14, 0, s);
+DEFINE_AD7380_4_OFFLOAD_CHANNEL(ad7383_4_offload_channels, 16, 0, s);
+DEFINE_AD7380_4_OFFLOAD_CHANNEL(ad7384_4_offload_channels, 14, 0, s);
+
+/* Single ended */
+DEFINE_AD7380_4_OFFLOAD_CHANNEL(ad7386_offload_channels, 16, 0, u);
+DEFINE_AD7380_4_OFFLOAD_CHANNEL(ad7387_offload_channels, 14, 0, u);
+DEFINE_AD7380_4_OFFLOAD_CHANNEL(ad7388_offload_channels, 12, 0, u);
+DEFINE_AD7380_8_OFFLOAD_CHANNEL(ad7386_4_offload_channels, 16, 0, u);
+DEFINE_AD7380_8_OFFLOAD_CHANNEL(ad7387_4_offload_channels, 14, 0, u);
+DEFINE_AD7380_8_OFFLOAD_CHANNEL(ad7388_4_offload_channels, 12, 0, u);
+
 static const char * const ad7380_supplies[] = {
 	"vcc", "vlogic",
 };
@@ -407,28 +601,33 @@ static const int ad7380_gains[] = {
 static const struct ad7380_chip_info ad7380_chip_info = {
 	.name = "ad7380",
 	.channels = ad7380_channels,
+	.offload_channels = ad7380_offload_channels,
 	.num_channels = ARRAY_SIZE(ad7380_channels),
 	.num_simult_channels = 2,
 	.supplies = ad7380_supplies,
 	.num_supplies = ARRAY_SIZE(ad7380_supplies),
 	.available_scan_masks = ad7380_2_channel_scan_masks,
 	.timing_specs = &ad7380_timing,
+	.max_conversion_rate_hz = 4 * MEGA,
 };
 
 static const struct ad7380_chip_info ad7381_chip_info = {
 	.name = "ad7381",
 	.channels = ad7381_channels,
+	.offload_channels = ad7381_offload_channels,
 	.num_channels = ARRAY_SIZE(ad7381_channels),
 	.num_simult_channels = 2,
 	.supplies = ad7380_supplies,
 	.num_supplies = ARRAY_SIZE(ad7380_supplies),
 	.available_scan_masks = ad7380_2_channel_scan_masks,
 	.timing_specs = &ad7380_timing,
+	.max_conversion_rate_hz = 4 * MEGA,
 };
 
 static const struct ad7380_chip_info ad7383_chip_info = {
 	.name = "ad7383",
 	.channels = ad7383_channels,
+	.offload_channels = ad7383_offload_channels,
 	.num_channels = ARRAY_SIZE(ad7383_channels),
 	.num_simult_channels = 2,
 	.supplies = ad7380_supplies,
@@ -437,11 +636,13 @@ static const struct ad7380_chip_info ad7383_chip_info = {
 	.num_vcm_supplies = ARRAY_SIZE(ad7380_2_channel_vcm_supplies),
 	.available_scan_masks = ad7380_2_channel_scan_masks,
 	.timing_specs = &ad7380_timing,
+	.max_conversion_rate_hz = 4 * MEGA,
 };
 
 static const struct ad7380_chip_info ad7384_chip_info = {
 	.name = "ad7384",
 	.channels = ad7384_channels,
+	.offload_channels = ad7384_offload_channels,
 	.num_channels = ARRAY_SIZE(ad7384_channels),
 	.num_simult_channels = 2,
 	.supplies = ad7380_supplies,
@@ -450,11 +651,13 @@ static const struct ad7380_chip_info ad7384_chip_info = {
 	.num_vcm_supplies = ARRAY_SIZE(ad7380_2_channel_vcm_supplies),
 	.available_scan_masks = ad7380_2_channel_scan_masks,
 	.timing_specs = &ad7380_timing,
+	.max_conversion_rate_hz = 4 * MEGA,
 };
 
 static const struct ad7380_chip_info ad7386_chip_info = {
 	.name = "ad7386",
 	.channels = ad7386_channels,
+	.offload_channels = ad7386_offload_channels,
 	.num_channels = ARRAY_SIZE(ad7386_channels),
 	.num_simult_channels = 2,
 	.supplies = ad7380_supplies,
@@ -462,11 +665,13 @@ static const struct ad7380_chip_info ad7386_chip_info = {
 	.has_mux = true,
 	.available_scan_masks = ad7380_2x2_channel_scan_masks,
 	.timing_specs = &ad7380_timing,
+	.max_conversion_rate_hz = 4 * MEGA,
 };
 
 static const struct ad7380_chip_info ad7387_chip_info = {
 	.name = "ad7387",
 	.channels = ad7387_channels,
+	.offload_channels = ad7387_offload_channels,
 	.num_channels = ARRAY_SIZE(ad7387_channels),
 	.num_simult_channels = 2,
 	.supplies = ad7380_supplies,
@@ -474,11 +679,13 @@ static const struct ad7380_chip_info ad7387_chip_info = {
 	.has_mux = true,
 	.available_scan_masks = ad7380_2x2_channel_scan_masks,
 	.timing_specs = &ad7380_timing,
+	.max_conversion_rate_hz = 4 * MEGA,
 };
 
 static const struct ad7380_chip_info ad7388_chip_info = {
 	.name = "ad7388",
 	.channels = ad7388_channels,
+	.offload_channels = ad7388_offload_channels,
 	.num_channels = ARRAY_SIZE(ad7388_channels),
 	.num_simult_channels = 2,
 	.supplies = ad7380_supplies,
@@ -486,11 +693,13 @@ static const struct ad7380_chip_info ad7388_chip_info = {
 	.has_mux = true,
 	.available_scan_masks = ad7380_2x2_channel_scan_masks,
 	.timing_specs = &ad7380_timing,
+	.max_conversion_rate_hz = 4 * MEGA,
 };
 
 static const struct ad7380_chip_info ad7380_4_chip_info = {
 	.name = "ad7380-4",
 	.channels = ad7380_4_channels,
+	.offload_channels = ad7380_4_offload_channels,
 	.num_channels = ARRAY_SIZE(ad7380_4_channels),
 	.num_simult_channels = 4,
 	.supplies = ad7380_supplies,
@@ -498,22 +707,26 @@ static const struct ad7380_chip_info ad7380_4_chip_info = {
 	.external_ref_only = true,
 	.available_scan_masks = ad7380_4_channel_scan_masks,
 	.timing_specs = &ad7380_4_timing,
+	.max_conversion_rate_hz = 4 * MEGA,
 };
 
 static const struct ad7380_chip_info ad7381_4_chip_info = {
 	.name = "ad7381-4",
 	.channels = ad7381_4_channels,
+	.offload_channels = ad7381_4_offload_channels,
 	.num_channels = ARRAY_SIZE(ad7381_4_channels),
 	.num_simult_channels = 4,
 	.supplies = ad7380_supplies,
 	.num_supplies = ARRAY_SIZE(ad7380_supplies),
 	.available_scan_masks = ad7380_4_channel_scan_masks,
 	.timing_specs = &ad7380_4_timing,
+	.max_conversion_rate_hz = 4 * MEGA,
 };
 
 static const struct ad7380_chip_info ad7383_4_chip_info = {
 	.name = "ad7383-4",
 	.channels = ad7383_4_channels,
+	.offload_channels = ad7383_4_offload_channels,
 	.num_channels = ARRAY_SIZE(ad7383_4_channels),
 	.num_simult_channels = 4,
 	.supplies = ad7380_supplies,
@@ -522,11 +735,13 @@ static const struct ad7380_chip_info ad7383_4_chip_info = {
 	.num_vcm_supplies = ARRAY_SIZE(ad7380_4_channel_vcm_supplies),
 	.available_scan_masks = ad7380_4_channel_scan_masks,
 	.timing_specs = &ad7380_4_timing,
+	.max_conversion_rate_hz = 4 * MEGA,
 };
 
 static const struct ad7380_chip_info ad7384_4_chip_info = {
 	.name = "ad7384-4",
 	.channels = ad7384_4_channels,
+	.offload_channels = ad7384_4_offload_channels,
 	.num_channels = ARRAY_SIZE(ad7384_4_channels),
 	.num_simult_channels = 4,
 	.supplies = ad7380_supplies,
@@ -535,11 +750,13 @@ static const struct ad7380_chip_info ad7384_4_chip_info = {
 	.num_vcm_supplies = ARRAY_SIZE(ad7380_4_channel_vcm_supplies),
 	.available_scan_masks = ad7380_4_channel_scan_masks,
 	.timing_specs = &ad7380_4_timing,
+	.max_conversion_rate_hz = 4 * MEGA,
 };
 
 static const struct ad7380_chip_info ad7386_4_chip_info = {
 	.name = "ad7386-4",
 	.channels = ad7386_4_channels,
+	.offload_channels = ad7386_4_offload_channels,
 	.num_channels = ARRAY_SIZE(ad7386_4_channels),
 	.num_simult_channels = 4,
 	.supplies = ad7380_supplies,
@@ -547,11 +764,13 @@ static const struct ad7380_chip_info ad7386_4_chip_info = {
 	.has_mux = true,
 	.available_scan_masks = ad7380_2x4_channel_scan_masks,
 	.timing_specs = &ad7380_4_timing,
+	.max_conversion_rate_hz = 4 * MEGA,
 };
 
 static const struct ad7380_chip_info ad7387_4_chip_info = {
 	.name = "ad7387-4",
 	.channels = ad7387_4_channels,
+	.offload_channels = ad7387_4_offload_channels,
 	.num_channels = ARRAY_SIZE(ad7387_4_channels),
 	.num_simult_channels = 4,
 	.supplies = ad7380_supplies,
@@ -559,11 +778,13 @@ static const struct ad7380_chip_info ad7387_4_chip_info = {
 	.has_mux = true,
 	.available_scan_masks = ad7380_2x4_channel_scan_masks,
 	.timing_specs = &ad7380_4_timing,
+	.max_conversion_rate_hz = 4 * MEGA,
 };
 
 static const struct ad7380_chip_info ad7388_4_chip_info = {
 	.name = "ad7388-4",
 	.channels = ad7388_4_channels,
+	.offload_channels = ad7388_4_offload_channels,
 	.num_channels = ARRAY_SIZE(ad7388_4_channels),
 	.num_simult_channels = 4,
 	.supplies = ad7380_supplies,
@@ -571,11 +792,13 @@ static const struct ad7380_chip_info ad7388_4_chip_info = {
 	.has_mux = true,
 	.available_scan_masks = ad7380_2x4_channel_scan_masks,
 	.timing_specs = &ad7380_4_timing,
+	.max_conversion_rate_hz = 4 * MEGA,
 };
 
 static const struct ad7380_chip_info adaq4370_4_chip_info = {
 	.name = "adaq4370-4",
 	.channels = adaq4380_4_channels,
+	.offload_channels = adaq4380_4_offload_channels,
 	.num_channels = ARRAY_SIZE(adaq4380_4_channels),
 	.num_simult_channels = 4,
 	.supplies = adaq4380_supplies,
@@ -584,11 +807,13 @@ static const struct ad7380_chip_info adaq4370_4_chip_info = {
 	.has_hardware_gain = true,
 	.available_scan_masks = ad7380_4_channel_scan_masks,
 	.timing_specs = &ad7380_4_timing,
+	.max_conversion_rate_hz = 2 * MEGA,
 };
 
 static const struct ad7380_chip_info adaq4380_4_chip_info = {
 	.name = "adaq4380-4",
 	.channels = adaq4380_4_channels,
+	.offload_channels = adaq4380_4_offload_channels,
 	.num_channels = ARRAY_SIZE(adaq4380_4_channels),
 	.num_simult_channels = 4,
 	.supplies = adaq4380_supplies,
@@ -597,6 +822,12 @@ static const struct ad7380_chip_info adaq4380_4_chip_info = {
 	.has_hardware_gain = true,
 	.available_scan_masks = ad7380_4_channel_scan_masks,
 	.timing_specs = &ad7380_4_timing,
+	.max_conversion_rate_hz = 4 * MEGA,
+};
+
+static const struct spi_offload_config ad7380_offload_config = {
+	.capability_flags = SPI_OFFLOAD_CAP_TRIGGER |
+			    SPI_OFFLOAD_CAP_RX_STREAM_DMA,
 };
 
 struct ad7380_state {
@@ -614,6 +845,13 @@ struct ad7380_state {
 	struct spi_message normal_msg;
 	struct spi_transfer seq_xfer[4];
 	struct spi_message seq_msg;
+	struct spi_transfer offload_xfer;
+	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];
 	/*
 	 * DMA (thus cache coherency maintenance) requires the transfer buffers
 	 * to live in their own cache lines.
@@ -833,7 +1071,7 @@ static int ad7380_update_xfers(struct ad7380_state *st,
 		xfer[2].bits_per_word = xfer[3].bits_per_word =
 			scan_type->realbits;
 		xfer[2].len = xfer[3].len =
-			BITS_TO_BYTES(scan_type->storagebits) *
+			AD7380_SPI_BYTES(scan_type) *
 			st->chip_info->num_simult_channels;
 		xfer[3].rx_buf = xfer[2].rx_buf + xfer[2].len;
 		/* Additional delay required here when oversampling is enabled */
@@ -846,13 +1084,139 @@ static int ad7380_update_xfers(struct ad7380_state *st,
 		xfer[0].delay.value = t_convert;
 		xfer[0].delay.unit = SPI_DELAY_UNIT_NSECS;
 		xfer[1].bits_per_word = scan_type->realbits;
-		xfer[1].len = BITS_TO_BYTES(scan_type->storagebits) *
+		xfer[1].len = AD7380_SPI_BYTES(scan_type) *
 			st->chip_info->num_simult_channels;
 	}
 
 	return 0;
 }
 
+static int ad7380_set_sample_freq(struct ad7380_state *st, int val)
+{
+	struct spi_offload_trigger_config config = {
+		.type = SPI_OFFLOAD_TRIGGER_PERIODIC,
+		.periodic = {
+			.frequency_hz = val,
+		},
+	};
+	int ret;
+
+	ret = spi_offload_trigger_validate(st->offload_trigger, &config);
+	if (ret)
+		return ret;
+
+	st->offload_trigger_hz = config.periodic.frequency_hz;
+
+	return 0;
+}
+
+static int ad7380_init_offload_msg(struct ad7380_state *st,
+				   struct iio_dev *indio_dev)
+{
+	struct spi_transfer *xfer = &st->offload_xfer;
+	struct device *dev = &st->spi->dev;
+	const struct iio_scan_type *scan_type;
+	int oversampling_ratio;
+	int ret;
+
+	scan_type = iio_get_current_scan_type(indio_dev,
+					      &indio_dev->channels[0]);
+	if (IS_ERR(scan_type))
+		return PTR_ERR(scan_type);
+
+	if (st->chip_info->has_mux) {
+		int index;
+
+		ret = iio_active_scan_mask_index(indio_dev);
+		if (ret < 0)
+			return ret;
+
+		index = ret;
+		if (index == AD7380_SCAN_MASK_SEQ) {
+			ret = regmap_set_bits(st->regmap, AD7380_REG_ADDR_CONFIG1,
+					      AD7380_CONFIG1_SEQ);
+			if (ret)
+				return ret;
+
+			st->seq = true;
+		} else {
+			ret = ad7380_set_ch(st, index);
+			if (ret)
+				return ret;
+		}
+	}
+
+	ret = ad7380_get_osr(st, &oversampling_ratio);
+	if (ret)
+		return ret;
+
+	xfer->bits_per_word = scan_type->realbits;
+	xfer->offload_flags = SPI_OFFLOAD_XFER_RX_STREAM;
+	xfer->len = AD7380_SPI_BYTES(scan_type) * st->chip_info->num_simult_channels;
+
+	spi_message_init_with_transfers(&st->offload_msg, xfer, 1);
+	st->offload_msg.offload = st->offload;
+
+	ret = spi_optimize_message(st->spi, &st->offload_msg);
+	if (ret) {
+		dev_err(dev, "failed to prepare offload msg, err: %d\n",
+			ret);
+		return ret;
+	}
+
+	return 0;
+}
+
+static int ad7380_offload_buffer_postenable(struct iio_dev *indio_dev)
+{
+	struct ad7380_state *st = iio_priv(indio_dev);
+	struct spi_offload_trigger_config config = {
+		.type = SPI_OFFLOAD_TRIGGER_PERIODIC,
+		.periodic = {
+			.frequency_hz = st->offload_trigger_hz,
+		},
+	};
+	int ret;
+
+	ret = ad7380_init_offload_msg(st, indio_dev);
+	if (ret)
+		return ret;
+
+	ret = spi_offload_trigger_enable(st->offload, st->offload_trigger, &config);
+	if (ret)
+		spi_unoptimize_message(&st->offload_msg);
+
+	return ret;
+}
+
+static int ad7380_offload_buffer_predisable(struct iio_dev *indio_dev)
+{
+	struct ad7380_state *st = iio_priv(indio_dev);
+	int ret;
+
+	if (st->seq) {
+		ret = regmap_update_bits(st->regmap,
+					 AD7380_REG_ADDR_CONFIG1,
+					 AD7380_CONFIG1_SEQ,
+					 FIELD_PREP(AD7380_CONFIG1_SEQ, 0));
+		if (ret)
+			return ret;
+
+		st->seq = false;
+	}
+
+	spi_offload_trigger_disable(st->offload, st->offload_trigger);
+
+	spi_unoptimize_message(&st->offload_msg);
+
+	return 0;
+}
+
+static const struct iio_buffer_setup_ops ad7380_offload_buffer_setup_ops = {
+	.postenable = ad7380_offload_buffer_postenable,
+	.predisable = ad7380_offload_buffer_predisable,
+};
+
 static int ad7380_triggered_buffer_preenable(struct iio_dev *indio_dev)
 {
 	struct ad7380_state *st = iio_priv(indio_dev);
@@ -983,7 +1347,7 @@ static int ad7380_read_direct(struct ad7380_state *st, unsigned int scan_index,
 	if (ret < 0)
 		return ret;
 
-	if (scan_type->storagebits > 16) {
+	if (scan_type->realbits > 16) {
 		if (scan_type->sign == 's')
 			*val = sign_extend32(*(u32 *)(st->scan_data + 4 * index),
 					     scan_type->realbits - 1);
@@ -1064,6 +1428,9 @@ static int ad7380_read_raw(struct iio_dev *indio_dev,
 		if (ret)
 			return ret;
 
+		return IIO_VAL_INT;
+	case IIO_CHAN_INFO_SAMP_FREQ:
+		*val = st->offload_trigger_hz;
 		return IIO_VAL_INT;
 	default:
 		return -EINVAL;
@@ -1075,6 +1442,8 @@ static int ad7380_read_avail(struct iio_dev *indio_dev,
 			     const int **vals, int *type, int *length,
 			     long mask)
 {
+	struct ad7380_state *st = iio_priv(indio_dev);
+
 	switch (mask) {
 	case IIO_CHAN_INFO_OVERSAMPLING_RATIO:
 		*vals = ad7380_oversampling_ratios;
@@ -1082,6 +1451,10 @@ static int ad7380_read_avail(struct iio_dev *indio_dev,
 		*type = IIO_VAL_INT;
 
 		return IIO_AVAIL_LIST;
+	case IIO_CHAN_INFO_SAMP_FREQ:
+		*vals = st->sample_freq_range;
+		*type = IIO_VAL_INT;
+		return IIO_AVAIL_RANGE;
 	default:
 		return -EINVAL;
 	}
@@ -1151,6 +1524,10 @@ static int ad7380_write_raw(struct iio_dev *indio_dev,
 	int ret;
 
 	switch (mask) {
+	case IIO_CHAN_INFO_SAMP_FREQ:
+		if (val < 1)
+			return -EINVAL;
+		return ad7380_set_sample_freq(st, val);
 	case IIO_CHAN_INFO_OVERSAMPLING_RATIO:
 		if (!iio_device_claim_direct(indio_dev))
 			return -EBUSY;
@@ -1380,6 +1757,53 @@ static int ad7380_init(struct ad7380_state *st, bool external_ref_en)
 					     AD7380_NUM_SDO_LINES));
 }
 
+static int ad7380_probe_spi_offload(struct iio_dev *indio_dev,
+				    struct ad7380_state *st)
+{
+	struct spi_device *spi = st->spi;
+	struct device *dev = &spi->dev;
+	struct dma_chan *rx_dma;
+	int sample_rate, ret;
+
+	indio_dev->setup_ops = &ad7380_offload_buffer_setup_ops;
+	indio_dev->channels = st->chip_info->offload_channels;
+	/* Just removing the timestamp channel. */
+	indio_dev->num_channels--;
+
+	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");
+
+	sample_rate = st->chip_info->max_conversion_rate_hz *
+		      AD7380_NUM_SDO_LINES / st->chip_info->num_simult_channels;
+
+	st->sample_freq_range[0] = 1; /* min */
+	st->sample_freq_range[1] = 1; /* step */
+	st->sample_freq_range[2] = sample_rate; /* max */
+
+	/*
+	 * Starting with a quite low frequency, to allow oversampling x32,
+	 * user is then reponsible to adjust the frequency for the specific case.
+	 */
+	ret = ad7380_set_sample_freq(st, sample_rate / 32);
+	if (ret)
+		return ret;
+
+	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");
+
+	ret = devm_iio_dmaengine_buffer_setup_with_handle(dev, indio_dev,
+		rx_dma, IIO_BUFFER_DIRECTION_IN);
+	if (ret)
+		return dev_err_probe(dev, ret, "cannot setup dma buffer\n");
+
+	return 0;
+}
+
 static int ad7380_probe(struct spi_device *spi)
 {
 	struct device *dev = &spi->dev;
@@ -1551,12 +1975,24 @@ static int ad7380_probe(struct spi_device *spi)
 	indio_dev->modes = INDIO_DIRECT_MODE;
 	indio_dev->available_scan_masks = st->chip_info->available_scan_masks;
 
-	ret = devm_iio_triggered_buffer_setup(dev, indio_dev,
-					      iio_pollfunc_store_time,
-					      ad7380_trigger_handler,
-					      &ad7380_buffer_setup_ops);
-	if (ret)
-		return ret;
+	st->offload = devm_spi_offload_get(dev, spi, &ad7380_offload_config);
+	ret = PTR_ERR_OR_ZERO(st->offload);
+	if (ret && ret != -ENODEV)
+		return dev_err_probe(dev, ret, "failed to get offload\n");
+
+	/* If no SPI offload, fall back to low speed usage. */
+	if (ret == -ENODEV) {
+		ret = devm_iio_triggered_buffer_setup(dev, indio_dev,
+						      iio_pollfunc_store_time,
+						      ad7380_trigger_handler,
+						      &ad7380_buffer_setup_ops);
+		if (ret)
+			return ret;
+	} else {
+		ret = ad7380_probe_spi_offload(indio_dev, st);
+		if (ret)
+			return ret;
+	}
 
 	ret = ad7380_init(st, external_ref_en);
 	if (ret)
@@ -1619,3 +2055,4 @@ module_spi_driver(ad7380_driver);
 MODULE_AUTHOR("Stefan Popa <stefan.popa@analog.com>");
 MODULE_DESCRIPTION("Analog Devices AD738x ADC driver");
 MODULE_LICENSE("GPL");
+MODULE_IMPORT_NS("IIO_DMAENGINE_BUFFER");

-- 
2.48.1

Re: [PATCH v3 1/2] iio: ad7380: add support for SPI offload

[Jonathan Cameron]

On Tue, 04 Mar 2025 16:25:44 +0100
Angelo Dureghello <adureghello@baylibre.com> wrote:

> Add support for SPI offload to the ad7380 driver. SPI offload allows
> sampling data at the max sample rate (2MSPS with one SDO line).
> 
> This is developed and tested against the ADI example FPGA design for
> this family of ADCs [1].
> 
> [1]: http://analogdevicesinc.github.io/hdl/projects/ad738x_fmc/index.html
> 
> Signed-off-by: Angelo Dureghello <adureghello@baylibre.com>
Hi Angelo

A couple of trivial comments inline.

This has crossed with Julien adding an extra device to the supported
set. I could have guessed what the necessary changes were but probably
better for you to do it and check for any problems.

https://lore.kernel.org/all/20250226-ad7380-add-adaq4381-4-support-v1-1-f350ab872d37@baylibre.com/

Jonathan

> ---
>  drivers/iio/adc/Kconfig  |   2 +
>  drivers/iio/adc/ad7380.c | 509 +++++++++++++++++++++++++++++++++++++++++++----
>  2 files changed, 475 insertions(+), 36 deletions(-)
> 
> diff --git a/drivers/iio/adc/Kconfig b/drivers/iio/adc/Kconfig
> index 27413516216cb3f83cf1d995b9ffc22bf01776a4..c528f4632c0ef6782269d8afa89c17d2046d28a3 100644
> --- a/drivers/iio/adc/Kconfig
> +++ b/drivers/iio/adc/Kconfig
> @@ -218,7 +218,9 @@ config AD7298
>  config AD7380
>  	tristate "Analog Devices AD7380 ADC driver"
>  	depends on SPI_MASTER
> +	select SPI_OFFLOAD
>  	select IIO_BUFFER
> +	select IIO_BUFFER_DMAENGINE
>  	select IIO_TRIGGER
>  	select IIO_TRIGGERED_BUFFER
>  	help
> diff --git a/drivers/iio/adc/ad7380.c b/drivers/iio/adc/ad7380.c
> index f232ad1a49634baeedc655916bc7a967604a1206..39a5e55fa7e8a6706e15750d07fa4b0fda7175eb 100644
> --- a/drivers/iio/adc/ad7380.c
> +++ b/drivers/iio/adc/ad7380.c
> @@ -15,6 +15,9 @@
>   * ad7386/7/8-4 : https://www.analog.com/media/en/technical-documentation/data-sheets/ad7386-4-7387-4-7388-4.pdf
>   * adaq4370-4 : https://www.analog.com/media/en/technical-documentation/data-sheets/adaq4370-4.pdf
>   * adaq4380-4 : https://www.analog.com/media/en/technical-documentation/data-sheets/adaq4380-4.pdf
> + *
> + * HDL ad738x_fmc: https://analogdevicesinc.github.io/hdl/projects/ad738x_fmc/index.html
> + *

Pet dislike of mine.  No lines at ends of comment blocks with nothing on them.  The */ provides
any necessary space.

>   */
>  
>  #include <linux/align.h>
> @@ -29,11 +32,13 @@
>  #include <linux/regmap.h>
>  #include <linux/regulator/consumer.h>
>  #include <linux/slab.h>
> +#include <linux/spi/offload/consumer.h>
>  #include <linux/spi/spi.h>
>  #include <linux/units.h>
>  #include <linux/util_macros.h>
>  
>  #include <linux/iio/buffer.h>
> +#include <linux/iio/buffer-dmaengine.h>
>  #include <linux/iio/events.h>
>  #include <linux/iio/iio.h>
>  #include <linux/iio/trigger_consumer.h>
> @@ -92,6 +97,12 @@
>  #define AD7380_NUM_SDO_LINES		1
>  #define AD7380_DEFAULT_GAIN_MILLI	1000
>  
> +/*
> + * Using SPI offload, storagebits is always 32, so can't be used to compute struct
> + * spi_transfer.len. Using realbits instead.
> + */
> +#define AD7380_SPI_BYTES(scan_type)	((scan_type)->realbits > 16 ? 4 : 2)
> +
>  struct ad7380_timing_specs {
>  	const unsigned int t_csh_ns;	/* CS minimum high time */
>  };
> @@ -99,6 +110,7 @@ struct ad7380_timing_specs {
>  struct ad7380_chip_info {
>  	const char *name;
>  	const struct iio_chan_spec *channels;
> +	const struct iio_chan_spec *offload_channels;
>  	unsigned int num_channels;
>  	unsigned int num_simult_channels;
>  	bool has_hardware_gain;
> @@ -111,6 +123,7 @@ struct ad7380_chip_info {
>  	unsigned int num_vcm_supplies;
>  	const unsigned long *available_scan_masks;
>  	const struct ad7380_timing_specs *timing_specs;
> +	u32 max_conversion_rate_hz;
>  };
>  
>  static const struct iio_event_spec ad7380_events[] = {
> @@ -216,6 +229,91 @@ static const struct iio_scan_type ad7380_scan_type_16_u[] = {
>  	},
>  };
>  
> +/*
> + * Defining here scan types for offload mode, since with current available HDL
> + * only a value of 32 for storagebits is supported.
> + */
> +
> +/* Extended scan types for 12-bit unsigned chips, offload support. */
> +static const struct iio_scan_type ad7380_scan_type_12_u_offload[] = {
> +	[AD7380_SCAN_TYPE_NORMAL] = {
> +		.sign = 'u',
> +		.realbits = 12,
> +		.storagebits = 32,
> +		.endianness = IIO_CPU,
> +	},
> +	[AD7380_SCAN_TYPE_RESOLUTION_BOOST] = {
> +		.sign = 'u',
> +		.realbits = 14,
> +		.storagebits = 32,
> +		.endianness = IIO_CPU,
> +	},
> +};
> +
> +/* Extended scan types for 14-bit signed chips, offload support. */
> +static const struct iio_scan_type ad7380_scan_type_14_s_offload[] = {
> +	[AD7380_SCAN_TYPE_NORMAL] = {
> +		.sign = 's',
> +		.realbits = 14,
> +		.storagebits = 32,
> +		.endianness = IIO_CPU,
> +	},
> +	[AD7380_SCAN_TYPE_RESOLUTION_BOOST] = {
> +		.sign = 's',
> +		.realbits = 16,
> +		.storagebits = 32,
> +		.endianness = IIO_CPU,
> +	},
> +};
> +
> +/* Extended scan types for 14-bit unsigned chips, offload support. */
> +static const struct iio_scan_type ad7380_scan_type_14_u_offload[] = {
> +	[AD7380_SCAN_TYPE_NORMAL] = {
> +		.sign = 'u',
> +		.realbits = 14,
> +		.storagebits = 32,
> +		.endianness = IIO_CPU,
> +	},
> +	[AD7380_SCAN_TYPE_RESOLUTION_BOOST] = {
> +		.sign = 'u',
> +		.realbits = 16,
> +		.storagebits = 32,
> +		.endianness = IIO_CPU,
> +	},
> +};
> +
> +/* Extended scan types for 16-bit signed_chips, offload support. */
> +static const struct iio_scan_type ad7380_scan_type_16_s_offload[] = {
> +	[AD7380_SCAN_TYPE_NORMAL] = {
> +		.sign = 's',
> +		.realbits = 16,
> +		.storagebits = 32,
> +		.endianness = IIO_CPU,
> +	},
> +	[AD7380_SCAN_TYPE_RESOLUTION_BOOST] = {
> +		.sign = 's',
> +		.realbits = 18,
> +		.storagebits = 32,
> +		.endianness = IIO_CPU,
> +	},
> +};
> +
> +/* Extended scan types for 16-bit unsigned chips, offload support. */
> +static const struct iio_scan_type ad7380_scan_type_16_u_offload[] = {
> +	[AD7380_SCAN_TYPE_NORMAL] = {
> +		.sign = 'u',
> +		.realbits = 16,
> +		.storagebits = 32,
> +		.endianness = IIO_CPU,
> +	},
> +	[AD7380_SCAN_TYPE_RESOLUTION_BOOST] = {
> +		.sign = 'u',
> +		.realbits = 18,
> +		.storagebits = 32,
> +		.endianness = IIO_CPU,
> +	},
> +};

You could have perhaps used a macro for these to reduce repetition but it
is perhaps slightly more readable without doing that.

Jonathan

[PATCH v3 2/2] docs: iio: ad7380: add SPI offload support

[Angelo Dureghello]

Document SPI offload support for the ad7380 driver.

Signed-off-by: Angelo Dureghello <adureghello@baylibre.com>
---
 Documentation/iio/ad7380.rst | 36 ++++++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/Documentation/iio/ad7380.rst b/Documentation/iio/ad7380.rst
index cff688bcc2d9601a9faf42d5e9c217486639ca66..12709ce051110e68b6f0c9b9a0baefcc954f2bc0 100644
--- a/Documentation/iio/ad7380.rst
+++ b/Documentation/iio/ad7380.rst
@@ -169,6 +169,42 @@ gain is selectable from device tree using the ``adi,gain-milli`` property.
 Refer to the typical connection diagrams section of the datasheet for pin
 wiring.
 
+
+SPI offload support
+-------------------
+
+To be able to achieve the maximum sample rate, the driver can be used with the
+`AXI SPI Engine`_ to provide SPI offload support.
+
+.. _AXI SPI Engine: http://analogdevicesinc.github.io/hdl/projects/ad738x_fmc/index.html
+
+When SPI offload is being used, some attributes will be different.
+
+* ``in_voltage-voltage_sampling_frequency`` attribute is added for setting the
+  sample rate.
+* ``in_voltage-voltage_sampling_frequency_available`` attribute is added for
+  querying the max sample rate.
+* ``timestamp`` channel is removed.
+* Buffer data format may be different compared to when offload is not used,
+  e.g. the ``buffer0/in_voltage0-voltage1_type`` and the
+  ``buffer0/in_voltage2-voltage3_type`` attributes.
+
+Effective sample rate for buffered reads
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Using SPI offload, the PWM generator drives the starting of the conversion by
+executing the pre-recorded SPI transfer at each PWM cycle, asserting CS and
+reading the previous available sample values for all channels.
+Default sample rate is set to a quite low frequency, to allow oversampling x32,
+user is then responsible to adjust ``in_voltage-voltage_sampling_frequency`` for
+the specific case.
+
+For single-ended chips where 2 banks of simultaneous inputs are available, as
+ad7386, ad7387 and ad7388, if at least one channel from each bank is enabled in
+a buffered read, the effective sample rate will be 1/2 of what is set as
+``in_voltage-voltage_sampling_frequency``, this because a separate conversion
+needs to be done for each bank.
+
 Unimplemented features
 ----------------------
 

-- 
2.48.1