iio: adc: Add support for LTC2378 and similar ADCs

From: Marcelo Schmitt <[email protected]>

Document how to describe LTC2378-20 and similar ADCs in device tree.

Signed-off-by Marcelo Schmitt <[email protected]>

---
 .../bindings/iio/adc/adi,ltc2378.yaml         | 131 ++++++++++++++++++
 MAINTAINERS                                   |   7 +
 2 files changed, 138 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/iio/adc/adi,ltc2378.yaml

Documentation/devicetree/bindings/iio/adc/adi,ltc2378.yaml new file +63 -0

new file mode 100644
index 000000000000..56e59bcd7306
@@ -0,0 +1,131 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/iio/adc/adi,ltc2378.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Analog Devices LTC2378 and similar Analog to Digital Converters
+
+maintainers:
+  - Marcelo Schmitt <[email protected]>
+
+description: |
+  Analog Devices LTC2378 series of ADCs.
+  Specifications can be found at:
+    https://www.analog.com/media/en/technical-documentation/data-sheets/233818fa.pdf
+    https://www.analog.com/media/en/technical-documentation/data-sheets/236416fa.pdf
+    https://www.analog.com/media/en/technical-documentation/data-sheets/236418f.pdf
+    https://www.analog.com/media/en/technical-documentation/data-sheets/236716fa.pdf
+    https://www.analog.com/media/en/technical-documentation/data-sheets/236718f.pdf
+    https://www.analog.com/media/en/technical-documentation/data-sheets/236816f.pdf
+    https://www.analog.com/media/en/technical-documentation/data-sheets/236818f.pdf
+    https://www.analog.com/media/en/technical-documentation/data-sheets/236918fa.pdf
+    https://www.analog.com/media/en/technical-documentation/data-sheets/237016fa.pdf
+    https://www.analog.com/media/en/technical-documentation/data-sheets/237616fa.pdf
+    https://www.analog.com/media/en/technical-documentation/data-sheets/237618fa.pdf
+    https://www.analog.com/media/en/technical-documentation/data-sheets/237620fb.pdf
+    https://www.analog.com/media/en/technical-documentation/data-sheets/237716fa.pdf
+    https://www.analog.com/media/en/technical-documentation/data-sheets/237718fa.pdf
+    https://www.analog.com/media/en/technical-documentation/data-sheets/237720fb.pdf
+    https://www.analog.com/media/en/technical-documentation/data-sheets/237816fa.pdf
+    https://www.analog.com/media/en/technical-documentation/data-sheets/237818fa.pdf
+    https://www.analog.com/media/en/technical-documentation/data-sheets/237820fb.pdf
+    https://www.analog.com/media/en/technical-documentation/data-sheets/237918fb.pdf
+    https://www.analog.com/media/en/technical-documentation/data-sheets/238016fb.pdf
+
+$ref: /schemas/spi/spi-peripheral-props.yaml#
+
+properties:
+  compatible:
+    oneOf:
+      - enum:
+          - adi,ltc2338-18
+          - adi,ltc2369-18
+          - adi,ltc2370-16
+          - adi,ltc2379-18
+          - adi,ltc2380-16
+      - items:
+          - enum:
+              - adi,ltc2364-18
+              - adi,ltc2364-16 # fallback compatible
+      - items:
+          - enum:
+              - adi,ltc2367-18
+              - adi,ltc2367-16 # fallback compatible
+      - items:
+          - enum:
+              - adi,ltc2368-18
+              - adi,ltc2368-16 # fallback compatible
+      - items:
+          - enum:
+              - adi,ltc2376-18
+              - adi,ltc2376-20
+              - adi,ltc2376-16 # fallback compatible

Documentation/devicetree/bindings/iio/adc/adi,ltc2378.yaml new file +28 -0

+
+  reg:
+    maxItems: 1
+
+  spi-max-frequency:
+    maximum: 100000000
+
+  vdd-supply:
+    description: A 2.5V supply that powers the chip (VDD).
+
+  ovdd-supply:
+    description:
+      A 1.71V to 5.25V supply that sets the logic level for digital interface.
+
+  ref-supply:
+    description:
+      A 2.5V to 5.1V supply for the reference input (REF).
+
+  cnv-gpios:
+    description:
+      When provided, this property indicates the GPIO that is connected to the
+      CNV pin.
+    maxItems: 1
+
+  interrupts:
+    description:
+      Interrupt for signaling the completion of conversion results. The active
+      low signal provided on the BUSY pin asserts when ADC conversions finish.

Documentation/devicetree/bindings/iio/adc/adi,ltc2378.yaml new file +20 -0

+
+examples:
+  - |
+    #include <dt-bindings/gpio/gpio.h>
+    #include <dt-bindings/interrupt-controller/irq.h>
+    spi {
+        #address-cells = <1>;
+        #size-cells = <0>;
+        adc@0 {
+            compatible = "adi,ltc2378-20";
+            reg = <0>;
+            spi-max-frequency = <71000000>;
+            vdd-supply = <&supply_2_5V>;
+            ovdd-supply = <&supply_3_3V>;
+            ref-supply = <&supply_5V>;
+            cnv-gpios = <&gpio0 88 GPIO_ACTIVE_HIGH>;
+            interrupts = <7 IRQ_TYPE_EDGE_FALLING>;
+            interrupt-parent = <&gpio>;
+        };
+    };

MAINTAINERS +7 -0

index 0de74503df08..768f56eea476 100644
@@ -15195,6 +15195,13 @@ S:	Maintained
 F:	Documentation/devicetree/bindings/iio/dac/lltc,ltc1660.yaml
 F:	drivers/iio/dac/ltc1660.c
 
+LTC2378 IIO ADC DRIVER
+M:	Marcelo Schmitt <[email protected]>
+L:	[email protected]
+S:	Supported
+W:	https://ez.analog.com/linux-software-drivers
+F:	Documentation/devicetree/bindings/iio/adc/adi,ltc2378.yaml
+
 LTC2664 IIO DAC DRIVER
 M:	Michael Hennerich <[email protected]>
 M:	Kim Seer Paller <[email protected]>

Signature · 1 line

2.53.0

Quoted 6 lines · Marcelo Schmitt

From: Marcelo Schmitt <[email protected]>

Document how to describe LTC2378-20 and similar ADCs in device tree.

Signed-off-by Marcelo Schmitt <[email protected]>

---

Quoted 26 lines

Documentation/devicetree/bindings/iio/adc/adi,ltc2378.yaml new file +26 -0

+properties:
+  compatible:
+    oneOf:
+      - enum:
+          - adi,ltc2338-18
+          - adi,ltc2369-18
+          - adi,ltc2370-16
+          - adi,ltc2379-18
+          - adi,ltc2380-16
+      - items:
+          - enum:
+              - adi,ltc2364-18
+              - adi,ltc2364-16 # fallback compatible
+      - items:
+          - enum:
+              - adi,ltc2367-18
+              - adi,ltc2367-16 # fallback compatible
+      - items:
+          - enum:
+              - adi,ltc2368-18
+              - adi,ltc2368-16 # fallback compatible
+      - items:
+          - enum:
+              - adi,ltc2376-18
+              - adi,ltc2376-20
+              - adi,ltc2376-16 # fallback compatible

Documentation/devicetree/bindings/iio/adc/adi,ltc2378.yaml line 73

Quoted 10 lines

Documentation/devicetree/bindings/iio/adc/adi,ltc2378.yaml new file +10 -0

+      - items:
+          - enum:
+              - adi,ltc2377-18
+              - adi,ltc2377-20
+              - adi,ltc2377-16 # fallback compatible
+      - items:
+          - enum:
+              - adi,ltc2378-18
+              - adi,ltc2378-20
+              - adi,ltc2378-16 # fallback compatible

All of these are wrong.

Firstly, your "fallback" setups don't work, because they only permit a single compatible. Secondly, if they did work, you still need to define the fallback compatible in isolation for it to be permitted for use when it isn't a fallback.
And thirdly, your driver appears to show that these devices aren't actually compatible at all, given there's unique match data for each one.

Why do you have fallbacks here? Is it because a limited set of channels could be used in the fallback case? At the very least, the rationale for fallbacks should be explained.

Review

Quoted 2 lines

(quoted diff) +2 -0

+
+additionalProperties: false

As sashiko pointed out, this is not correct if you want to permit spi properties other than spi-max-frequency (although I could definitely see how this would be correct).

From: Marcelo Schmitt <[email protected]>

Initial support for LTC2378-20 and similar analog-to-digital converters.

Signed-off-by Marcelo Schmitt <[email protected]>

---
The data union for the sample data and the filling of IIO channel scan_type struct could probably have been avoided and postponed. Though, that would probably imply larger git diffs in the buffer patches so I added those earlier to minimize diff size in the buffer patches.

drivers/iio/adc/Makefile +1 -0

index 707dd708912f..1814fb78dde3 100644
@@ -81,6 +81,7 @@ obj-$(CONFIG_LP8788_ADC) += lp8788_adc.o
 obj-$(CONFIG_LPC18XX_ADC) += lpc18xx_adc.o
 obj-$(CONFIG_LPC32XX_ADC) += lpc32xx_adc.o
 obj-$(CONFIG_LTC2309) += ltc2309.o
+obj-$(CONFIG_LTC2378) += ltc2378.o
 obj-$(CONFIG_LTC2471) += ltc2471.o
 obj-$(CONFIG_LTC2485) += ltc2485.o
 obj-$(CONFIG_LTC2496) += ltc2496.o ltc2497-core.o

drivers/iio/adc/ltc2378.c new file +4 -0

new file mode 100644
index 000000000000..7916500c470c
@@ -0,0 +1,352 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Analog Devices LTC2378 ADC series driver
+ *

drivers/iio/adc/ltc2378.c new file +4 -0

+
+#include "ltc2378.h"
+
+enum ltc2378_supported_device_ids {

drivers/iio/adc/ltc2378.c new file +8 -0

+	ret = spi_sync_transfer(st->spi, &st->xfer, 1);
+	gpiod_set_value_cansleep(st->cnv_gpio, 0);
+
+	return ret;
+}
+
+static int ltc2378_channel_single_read(const struct iio_chan_spec *chan,
+				       struct ltc2378_state *st, int *val)

drivers/iio/adc/ltc2378.c new file +20 -0

+		if (scan_type->realbits > 16)
+			sample = be32_to_cpu(st->scan.data.sample_buf32_be);
+		else
+			sample = be16_to_cpu(st->scan.data.sample_buf16_be);
+	} else {
+		if (scan_type->realbits > 16)
+			sample = st->scan.data.sample_buf32;
+		else
+			sample = st->scan.data.sample_buf16;
+	}
+
+	sample >>= scan_type->shift;
+
+	if (scan_type->format == IIO_SCAN_FORMAT_SIGNED_INT)
+		*val = sign_extend32(sample, scan_type->realbits - 1);
+	else
+		*val = sample;
+
+	return 0;
+}

drivers/iio/adc/ltc2378.c new file +40 -0

+		IIO_DEV_ACQUIRE_DIRECT_MODE(indio_dev, claim);
+		if (IIO_DEV_ACQUIRE_FAILED(claim))
+			return -EBUSY;
+
+		ret = ltc2378_channel_single_read(chan, st, val);
+		if (ret)
+			return ret;
+
+		return IIO_VAL_INT;
+
+	case IIO_CHAN_INFO_SCALE:
+		*val = st->ref_uV / MILLI;
+		/*
+		 * For all LTC2378-like devices, the amount of bits that express
+		 * voltage magnitude depend on the output code format:
+		 * - straight binary: All precision/resolution bits are used.
+		 * - 2's complement: One of the precision bits is used for sign.
+		 */
+		if (st->info->out_format == IIO_SCAN_FORMAT_SIGNED_INT)
+			*val2 = st->info->resolution - 1;
+		else
+			*val2 = st->info->resolution;
+
+		return IIO_VAL_FRACTIONAL_LOG2;
+
+	default:
+		return -EINVAL;
+	}
+}
+
+static const struct iio_info ltc2378_iio_info = {
+	.read_raw = &ltc2378_read_raw,
+};
+
+static int ltc2378_probe(struct spi_device *spi)
+{
+	struct iio_chan_spec *ltc2378_chan;
+	struct device *dev = &spi->dev;
+	unsigned int num_iio_chans = 1;
+	struct iio_dev *indio_dev;

drivers/iio/adc/ltc2378.c new file +7 -0

+	if (st->ref_uV < 0)
+		return dev_err_probe(dev, -ENODEV, "failed to read ref regulator\n");
+
+	st->info = spi_get_device_match_data(spi);
+	if (!st->info)
+		return -EINVAL;
+

drivers/iio/adc/ltc2378.c new file +20 -0

+	st->xfer.rx_buf = &st->scan.data;
+	st->xfer.len = BITS_TO_BYTES(ltc2378_chan->scan_type.storagebits);
+
+	indio_dev->channels = ltc2378_chan;
+	indio_dev->num_channels = num_iio_chans;
+
+	return devm_iio_device_register(&spi->dev, indio_dev);
+}
+
+static const struct of_device_id ltc2378_of_match[] = {
+	{ .compatible = "adi,ltc2338-18", .data = &ltc2378_chip_info[ID_LTC2338_18] },
+	{ .compatible = "adi,ltc2364-16", .data = &ltc2378_chip_info[ID_LTC2364_16] },
+	{ .compatible = "adi,ltc2364-18", .data = &ltc2378_chip_info[ID_LTC2364_18] },
+	{ .compatible = "adi,ltc2367-16", .data = &ltc2378_chip_info[ID_LTC2367_16] },
+	{ .compatible = "adi,ltc2367-18", .data = &ltc2378_chip_info[ID_LTC2367_18] },
+	{ .compatible = "adi,ltc2368-16", .data = &ltc2378_chip_info[ID_LTC2368_16] },
+	{ .compatible = "adi,ltc2368-18", .data = &ltc2378_chip_info[ID_LTC2368_18] },
+	{ .compatible = "adi,ltc2369-18", .data = &ltc2378_chip_info[ID_LTC2369_18] },
+	{ .compatible = "adi,ltc2370-16", .data = &ltc2378_chip_info[ID_LTC2370_16] },
+	{ .compatible = "adi,ltc2376-16", .data = &ltc2378_chip_info[ID_LTC2376_16] },

drivers/iio/adc/ltc2378.c new file +15 -0

+};
+MODULE_DEVICE_TABLE(of, ltc2378_of_match);
+
+static const struct spi_device_id ltc2378_spi_id[] = {
+	{ "ltc2338-18", (kernel_ulong_t)&ltc2378_chip_info[ID_LTC2338_18] },
+	{ "ltc2364-16", (kernel_ulong_t)&ltc2378_chip_info[ID_LTC2364_16] },
+	{ "ltc2364-18", (kernel_ulong_t)&ltc2378_chip_info[ID_LTC2364_18] },
+	{ "ltc2367-16", (kernel_ulong_t)&ltc2378_chip_info[ID_LTC2367_16] },
+	{ "ltc2367-18", (kernel_ulong_t)&ltc2378_chip_info[ID_LTC2367_18] },
+	{ "ltc2368-16", (kernel_ulong_t)&ltc2378_chip_info[ID_LTC2368_16] },
+	{ "ltc2368-18", (kernel_ulong_t)&ltc2378_chip_info[ID_LTC2368_18] },
+	{ "ltc2369-18", (kernel_ulong_t)&ltc2378_chip_info[ID_LTC2369_18] },
+	{ "ltc2370-16", (kernel_ulong_t)&ltc2378_chip_info[ID_LTC2370_16] },
+	{ "ltc2376-16", (kernel_ulong_t)&ltc2378_chip_info[ID_LTC2376_16] },
+	{ "ltc2376-18", (kernel_ulong_t)&ltc2378_chip_info[ID_LTC2376_18] },

drivers/iio/adc/ltc2378.c new file +2 -0

+};
+MODULE_DEVICE_TABLE(spi, ltc2378_spi_id);

drivers/iio/adc/ltc2378.h new file +13 -0

new file mode 100644
index 000000000000..515f7e8a4f2e
@@ -0,0 +1,48 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Analog Devices LTC2378 and similar ADCs common definitions and properties
+ * Copyright (C) 2026 Analog Devices, Inc.
+ * Author: Marcelo Schmitt <[email protected]>
+ */
+
+#ifndef __DRIVERS_IIO_ADC_LTC2378_H__
+#define __DRIVERS_IIO_ADC_LTC2378_H__
+
+#include <linux/iio/iio.h>
+#include <linux/spi/spi.h>
+#include <linux/types.h>

drivers/iio/adc/ltc2378.h new file +25 -0

+};
+
+struct ltc2378_state {
+	const struct ltc2378_chip_info *info;
+	struct gpio_desc *cnv_gpio;
+	struct spi_device *spi;
+	struct spi_transfer xfer;
+	int ref_uV;
+
+	/*
+	 * DMA (thus cache coherency maintenance) requires the
+	 * transfer buffers to live in their own cache lines.
+	 */
+	struct {
+		union {
+			__be16 sample_buf16_be;
+			__be32 sample_buf32_be;
+			u16 sample_buf16;
+			u32 sample_buf32;
+		} data;
+		aligned_s64 timestamp;
+	} scan __aligned(IIO_DMA_MINALIGN);
+};
+
+#endif /* __DRIVERS_IIO_ADC_LTC2378_H__ */

From: Marcelo Schmitt <[email protected]>

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

Signed-off-by Marcelo Schmitt <[email protected]>

---
 drivers/iio/adc/Kconfig                  |  12 +
 drivers/iio/adc/Makefile                 |   1 +
 drivers/iio/adc/ltc2378-offload-buffer.c | 297 +++++++++++++++++++++++
 drivers/iio/adc/ltc2378.c                |  62 +++++
 drivers/iio/adc/ltc2378.h                |  34 +++
 5 files changed, 406 insertions(+)
 create mode 100644 drivers/iio/adc/ltc2378-offload-buffer.c

drivers/iio/adc/Kconfig +1 -0

index 70fec8e3e891..b5368ee783f7 100644
@@ -944,6 +944,7 @@ config LTC2378
 	depends on SPI
 	depends on GPIOLIB || PWM
 	select IIO_BUFFER
+	imply LTC2378_OFFLOAD_BUFFER
 	help
 	  Say yes here to build support for Analog Devices LTC2378-20 and
 	  similar analog to digital converters.

@@ -951,6 +952,17 @@ config LTC2378
 	  This driver can also be built as a module. If so, the module will

drivers/iio/adc/Kconfig +3 -0

+	help
+	  Say yes here to build support for high speed data capture with LTC2378
+
 config LTC2471
 	tristate "Linear Technology LTC2471 and LTC2473 ADC driver"
 	depends on I2C

drivers/iio/adc/Makefile +0 -0

index 1814fb78dde3..2fa5dce0ceea 100644

drivers/iio/adc/Makefile +0 -0

 obj-$(CONFIG_LTC2471) += ltc2471.o
 obj-$(CONFIG_LTC2485) += ltc2485.o
 obj-$(CONFIG_LTC2496) += ltc2496.o ltc2497-core.o

drivers/iio/adc/ltc2378-offload-buffer.c new file +2 -0

new file mode 100644
index 000000000000..ed09f9a55f93
@@ -0,0 +1,297 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*

drivers/iio/adc/ltc2378-offload-buffer.c new file +45 -0

+#include <linux/kstrtox.h>
+#include <linux/limits.h>
+#include <linux/linkage.h>
+#include <linux/math.h>
+#include <linux/math64.h>
+#include <linux/minmax.h>
+#include <linux/pwm.h>
+#include <linux/spi/offload/consumer.h>
+#include <linux/spi/offload/types.h>
+#include <linux/time64.h>
+
+#include "ltc2378.h"
+
+/*
+ * 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;
+	u64 offload_offset_ns;
+	int ret;
+
+	if (freq_Hz == 0)
+		return -EINVAL;
+

drivers/iio/adc/ltc2378-offload-buffer.c new file +32 -0

+	 */
+	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 (cnv_wf.duty_length_ns < LTC2378_TCNV_HIGH_NS);
+
+	/*
+	 * 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_ROUND_UP(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;
+	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 (config->periodic.offset_ns < min_read_offset);
+
+	st->cnv_wf = cnv_wf;
+	st->cnv_Hz = DIV_ROUND_CLOSEST_ULL(HZ_PER_GHZ, cnv_wf.period_length_ns);
+

drivers/iio/adc/ltc2378-offload-buffer.c new file +7 -0

+	.attrs = ltc2378_offload_attributes,
+};
+EXPORT_SYMBOL_NS_GPL(ltc2378_offload_attribute_group, "IIO_LTC2378");
+
+static int ltc2378_prepare_offload_message(struct device *dev,
+					   struct ltc2378_state *st)
+{

drivers/iio/adc/ltc2378-offload-buffer.c new file +9 -0

+
+	/* 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);
+}
 
+
+int ltc2378_offload_buffer_setup(struct iio_dev *indio_dev, struct spi_device *spi)

drivers/iio/adc/ltc2378-offload-buffer.c new file +14 -0

+	 */
+	ret = ltc2378_update_conversion_rate(st, st->info->max_sample_rate_hz >> 4);
+	if (ret)
+		return dev_err_probe(dev, ret, "failed to sampling frequency\n");
+
+	ret = ltc2378_prepare_offload_message(&spi->dev, st);
+	if (ret)
+		return dev_err_probe(dev, ret, "failed to optimize SPI message\n");
+
+	return 0;
+}
+EXPORT_SYMBOL_NS_GPL(ltc2378_offload_buffer_setup, "IIO_LTC2378");
+
+MODULE_IMPORT_NS("IIO_LTC2378");

drivers/iio/adc/ltc2378.c +0 -0

index 7916500c470c..fdbe919d45d5 100644
 
 	[ID_LTC2378_16] = {
 		.name = "ltc2378-16",
 		.resolution = 16,

drivers/iio/adc/ltc2378.c +6 -0

 	},
 	[ID_LTC2378_20] = {
 		.name = "ltc2378-20",
 		.resolution = 20,
+		.max_sample_rate_hz = HZ_PER_MHZ,
+		.tconv_ns = 675,
 		.out_format = IIO_SCAN_FORMAT_SIGNED_INT,
 	},
 	[ID_LTC2379_18] = {
 		.name = "ltc2379-18",
 		.resolution = 18,
+		.max_sample_rate_hz = 1600 * HZ_PER_KHZ,
+		.tconv_ns = 412,
 		.out_format = IIO_SCAN_FORMAT_SIGNED_INT,
 	},
 	[ID_LTC2380_16] = {
 		.name = "ltc2380-16",
 		.resolution = 16,
+		.max_sample_rate_hz = 2 * HZ_PER_MHZ,
+		.tconv_ns = 322,
 		.out_format = IIO_SCAN_FORMAT_SIGNED_INT,
 	},
 };

drivers/iio/adc/ltc2378.c +3 -0

+	.attrs = &ltc2378_offload_attribute_group,
+#endif
 	.read_raw = &ltc2378_read_raw,
 };
 

@@ -236,6 +279,7 @@ static int ltc2378_probe(struct spi_device *spi)
 	unsigned int num_iio_chans = 1;
 	struct iio_dev *indio_dev;
 	struct ltc2378_state *st;
+	int ret;
 
 	indio_dev = devm_iio_device_alloc(&spi->dev, sizeof(*st));
 	if (!indio_dev)

drivers/iio/adc/ltc2378.c +3 -0

+	}
+
 	indio_dev->channels = ltc2378_chan;
 	indio_dev->num_channels = num_iio_chans;
 

@@ -350,3 +411,4 @@ MODULE_AUTHOR("Ioan-Daniel Pop <[email protected]>");
 MODULE_AUTHOR("Marcelo Schmitt <[email protected]>");
 MODULE_DESCRIPTION("Analog Devices LTC2378 ADC series driver");
 MODULE_LICENSE("GPL");
+MODULE_IMPORT_NS("IIO_LTC2378");

drivers/iio/adc/ltc2378.h +0 -0

index 515f7e8a4f2e..17c329b18333 100644

drivers/iio/adc/ltc2378.h +19 -0

+#include <linux/pwm.h>
+#endif
 #include <linux/spi/spi.h>
+#ifdef CONFIG_LTC2378_OFFLOAD_BUFFER
+#include <linux/spi/offload/consumer.h>
+#include <linux/spi/offload/types.h>
+#endif
 #include <linux/types.h>
 #include <linux/units.h>
 

@@ -20,6 +27,8 @@
 struct ltc2378_chip_info {
 	const char *name;
 	int resolution;
+	unsigned int max_sample_rate_hz;
+	unsigned int tconv_ns;
 	const char out_format;
 };
 

@@ -29,6 +38,16 @@ struct ltc2378_state {
 	struct spi_device *spi;
 	struct spi_transfer xfer;
 	int ref_uV;
+#ifdef CONFIG_LTC2378_OFFLOAD_BUFFER
+	unsigned int cnv_Hz;
+	struct pwm_waveform cnv_wf;
+	struct spi_offload *offload;
+	struct spi_offload_trigger *offload_trigger;
+	struct spi_message offload_msg;
+	struct spi_transfer offload_xfer;
+	struct spi_offload_trigger_config offload_trigger_config;
+	struct pwm_device *cnv_trigger;
+#endif
 
 	/*
 	 * DMA (thus cache coherency maintenance) requires the

@@ -45,4 +64,19 @@ struct ltc2378_state {
 	} scan __aligned(IIO_DMA_MINALIGN);
 };
 
+#ifdef CONFIG_LTC2378_OFFLOAD_BUFFER

drivers/iio/adc/ltc2378.h +4 -0

+	return -ENODEV;
+}
+#endif
+
 #endif /* __DRIVERS_IIO_ADC_LTC2378_H__ */

Quoted 16 lines

drivers/iio/adc/Kconfig +1 -0

index 70fec8e3e891..b5368ee783f7 100644
@@ -944,6 +944,7 @@ config LTC2378
 	depends on SPI
 	depends on GPIOLIB || PWM
 	select IIO_BUFFER
+	imply LTC2378_OFFLOAD_BUFFER
 	help
 	  Say yes here to build support for Analog Devices LTC2378-20 and
 	  similar analog to digital converters.

@@ -951,6 +952,17 @@ config LTC2378
 	  This driver can also be built as a module. If so, the module will
 	  be called ltc2378.
 

drivers/iio/adc/Kconfig config LTC2378 · line 962

Quoted 8 lines

drivers/iio/adc/Kconfig +8 -0

+config LTC2378_OFFLOAD_BUFFER
+	bool "Offloaded data capture with LTC2378"
+	depends on SPI && LTC2378
+	depends on SPI_OFFLOAD=y
+	depends on PWM=y
+	depends on SPI_OFFLOAD_TRIGGER_PWM=y
+	depends on IIO_BUFFER_DMA=y
+	depends on IIO_BUFFER_DMAENGINE=y

why do all these have to be built in? In general I think we need to jusitfy why this driver needs to work on systems with out this stuff being built. I.e. why do we need the separate optional file at all?

Quoted 13 lines

drivers/iio/adc/Kconfig +3 -0

+	help
+	  Say yes here to build support for high speed data capture with LTC2378
+
 config LTC2471
 	tristate "Linear Technology LTC2471 and LTC2473 ADC driver"
 	depends on I2C

drivers/iio/adc/Makefile +0 -0

index 1814fb78dde3..2fa5dce0ceea 100644
@@ -82,6 +82,7 @@ obj-$(CONFIG_LPC18XX_ADC) += lpc18xx_adc.o
 obj-$(CONFIG_LPC32XX_ADC) += lpc32xx_adc.o

drivers/iio/adc/Makefile obj-$(CONFIG_LPC18XX_ADC) += lpc18xx_adc.o · line 85

Quoted 3 lines

drivers/iio/adc/Makefile +1 -0

 obj-$(CONFIG_LTC2309) += ltc2309.o
 obj-$(CONFIG_LTC2378) += ltc2378.o
+obj-$(CONFIG_LTC2378_OFFLOAD_BUFFER) += ltc2378-offload-buffer.o

Hmm. This is odd. The driver can be modular but not this and it's build seperately rather than as part of the module. I think these bit needs a redesign. We definitely want this extra support to be part of the module. See how something like the ADIS IMU library in iio/imu/Makefile is done.

Quoted 4 lines

drivers/iio/adc/Makefile +0 -0

 obj-$(CONFIG_LTC2471) += ltc2471.o
 obj-$(CONFIG_LTC2485) += ltc2485.o
 obj-$(CONFIG_LTC2496) += ltc2496.o ltc2497-core.o

Quoted 16 lines

Quoted 16 lines

drivers/iio/adc/Kconfig +1 -0

index 70fec8e3e891..b5368ee783f7 100644
@@ -944,6 +944,7 @@ config LTC2378
 	depends on SPI
 	depends on GPIOLIB || PWM
 	select IIO_BUFFER
+	imply LTC2378_OFFLOAD_BUFFER
 	help
 	  Say yes here to build support for Analog Devices LTC2378-20 and
 	  similar analog to digital converters.

@@ -951,6 +952,17 @@ config LTC2378
 	  This driver can also be built as a module. If so, the module will
 	  be called ltc2378.
 

Quoted 12 lines

drivers/iio/adc/Kconfig config LTC2378 · line 962

Quoted 8 lines

drivers/iio/adc/Kconfig +8 -0

+config LTC2378_OFFLOAD_BUFFER
+	bool "Offloaded data capture with LTC2378"
+	depends on SPI && LTC2378
+	depends on SPI_OFFLOAD=y
+	depends on PWM=y
+	depends on SPI_OFFLOAD_TRIGGER_PWM=y
+	depends on IIO_BUFFER_DMA=y
+	depends on IIO_BUFFER_DMAENGINE=y  

why do all these have to be built in? In general I think we need to jusitfy why this driver needs to work on systems with out this stuff being built. I.e. why do we need the separate optional file at all?

Hi Jonathan, thank you for your review.

I've applied fixes to all issues reported by sashiko, except for Kconfig configuration (see below) and the is_visible() thing I'm still working on.

My intent with this design choice was to keep chip intrinsic dependencies separate from SPI offload dependencies. The indented benefit is to enable using the device without having to enable SPI_OFFLOAD (which is boolean and might not be supported on all platforms). The offload feature is indeed highly desirable hence the imply on the main driver Kconfig entry. The other symbols are tristate so, if we keep this approach, will drop =y.

The separate optional file is part of the push for dependency separation. It helps avoid #ifdef in c code. If the proposal is not far from something acceptable, I'd like to have another try of making it work. Still, it's arguable that the real interest is only on supporting the offload thing. Also, since I don't have any request to support these without offload, I think it will also be okay to have everything combined into a single driver.

Will follow all the other suggestions.

Quoted 13 lines

Quoted 13 lines

drivers/iio/adc/Kconfig +3 -0

+	help
+	  Say yes here to build support for high speed data capture with LTC2378
+
 config LTC2471
 	tristate "Linear Technology LTC2471 and LTC2473 ADC driver"
 	depends on I2C

drivers/iio/adc/Makefile +0 -0

index 1814fb78dde3..2fa5dce0ceea 100644
@@ -82,6 +82,7 @@ obj-$(CONFIG_LPC18XX_ADC) += lpc18xx_adc.o
 obj-$(CONFIG_LPC32XX_ADC) += lpc32xx_adc.o

Quoted 8 lines

drivers/iio/adc/Makefile obj-$(CONFIG_LPC18XX_ADC) += lpc18xx_adc.o · line 85

Quoted 3 lines

drivers/iio/adc/Makefile +1 -0

 obj-$(CONFIG_LTC2309) += ltc2309.o
 obj-$(CONFIG_LTC2378) += ltc2378.o
+obj-$(CONFIG_LTC2378_OFFLOAD_BUFFER) += ltc2378-offload-buffer.o  

Hmm. This is odd. The driver can be modular but not this and it's build seperately rather than as part of the module. I think these bit needs a redesign. We definitely want this extra support to be part of the module. See how something like the ADIS IMU library in iio/imu/Makefile is done.

Will check this out too.

Quoted 4 lines

Quoted 4 lines

drivers/iio/adc/Makefile +0 -0

 obj-$(CONFIG_LTC2471) += ltc2471.o
 obj-$(CONFIG_LTC2485) += ltc2485.o
 obj-$(CONFIG_LTC2496) += ltc2496.o ltc2497-core.o  

From: Marcelo Schmitt <[email protected]>

Enable users to run triggered data captures with LTC2378 and similar ADCs.

Signed-off-by Marcelo Schmitt <[email protected]>

---
 drivers/iio/adc/Kconfig   |  1 +
 drivers/iio/adc/ltc2378.c | 39 ++++++++++++++++++++++++++++++++++++---
 2 files changed, 37 insertions(+), 3 deletions(-)

drivers/iio/adc/Kconfig +1 -0

index b5368ee783f7..265c4a2b5fb7 100644
@@ -944,6 +944,7 @@ config LTC2378
 	depends on SPI
 	depends on GPIOLIB || PWM
 	select IIO_BUFFER
+	select IIO_TRIGGERED_BUFFER
 	imply LTC2378_OFFLOAD_BUFFER
 	help
 	  Say yes here to build support for Analog Devices LTC2378-20 and

drivers/iio/adc/ltc2378.c +22 -0

index fdbe919d45d5..993e6b09bb41 100644
@@ -10,6 +10,9 @@
 #include <linux/bitops.h>
 #include <linux/delay.h>
 #include <linux/err.h>
+#include <linux/iio/buffer.h>
+#include <linux/iio/triggered_buffer.h>
+#include <linux/iio/trigger_consumer.h>
 #include <linux/module.h>
 #include <linux/regulator/consumer.h>
 

@@ -272,6 +275,25 @@ static const struct iio_info ltc2378_iio_info = {
 	.read_raw = &ltc2378_read_raw,
 };
 
+static irqreturn_t ltc2378_trigger_handler(int irq, void *p)
+{
+	struct iio_poll_func *pf = p;
+	struct iio_dev *indio_dev = pf->indio_dev;
+	struct ltc2378_state *st = iio_priv(indio_dev);
+	int ret;
+
+	ret = ltc2378_convert_and_acquire(st);
+	if (ret < 0)
+		goto err_out;
+
+	iio_push_to_buffers_with_ts(indio_dev, &st->scan, sizeof(st->scan),
+				    pf->timestamp);
+
+err_out:
+	iio_trigger_notify_done(indio_dev->trig);
+	return IRQ_HANDLED;
+}
+
 static int ltc2378_probe(struct spi_device *spi)
 {
 	struct iio_chan_spec *ltc2378_chan;

drivers/iio/adc/ltc2378.c +1 -1

 	if (!ltc2378_chan)
 		return -ENOMEM;
 
-	*ltc2378_chan = (struct iio_chan_spec) {
+	ltc2378_chan[0] = (struct iio_chan_spec) {
 		.type = IIO_VOLTAGE,
 		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
 				      BIT(IIO_CHAN_INFO_SCALE),

@@ -327,7 +349,18 @@ static int ltc2378_probe(struct spi_device *spi)
 	ret = ltc2378_offload_buffer_setup(indio_dev, spi);
 	if (ret == -ENODEV) {
 		/* SPI offloading is unavailable. Fall back to triggered buffer. */

drivers/iio/adc/ltc2378.c +3 -0

+
+		ltc2378_chan[1] = ts_chan;
+		num_iio_chans++;
 	} else if (ret) {
 		return dev_err_probe(dev, ret, "error on SPI offload setup\n");
 	} else {