[PATCH v7 0/4] iio: adc: Add support for LTC2378 and similar ADCs

[PATCH v7 0/4] iio: adc: Add support for LTC2378 and similar ADCs

[Marcelo Schmitt]

This patch series adds support for LTC2378 and similar low noise, low power,
high speed, successive approximation register (SAR) ADCs. These ADCs are similar
among each other, varying mainly on the amount of precision bits, maximum sample
rate, and input configuration (either fully differential or pseudo-differential).

Patch 1 adds device tree documentation for LTC2378.

Patch 2 enables single-shot sample read with a GPIO connected to the LTC2378 CNV pin.

Patch 3 enables high-speed data captures with SPI offloading.
The setup is similar to AD4030, with a specialized PWM generator being used both
for SPI offload triggering and conversion start signaling.

Patch 4 enables running buffered data captures without SPI offloading.

Even though these parts are somewhat similar to AD4000, the wiring configuration
for LTC parts is different as well as the available HDL for high speed sample
rate mode. Because of that, I propose creating a new device driver for
supporting LTC2378-like devices.

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

Previous submissions:
  v6: https://lore.kernel.org/linux-iio/cover.1783629101.git.marcelo.schmitt@analog.com/
  v5: https://lore.kernel.org/linux-iio/cover.1783028033.git.marcelo.schmitt@analog.com/
  v4: https://lore.kernel.org/linux-iio/cover.1782397418.git.marcelo.schmitt@analog.com/
  v3: https://lore.kernel.org/linux-iio/cover.1781661028.git.marcelo.schmitt@analog.com/
  v2: https://lore.kernel.org/linux-iio/cover.1779976379.git.marcelo.schmitt@analog.com/
  v1: https://lore.kernel.org/linux-iio/cover.1779117444.git.marcelo.schmitt1@gmail.com/

Change log v6 -> v7:
[DT]
No changes in device tree doc.
[IIO]
- Extended single-read critical section scope (holding mutex lock longer).
- Added comment about conversion wait time.
- Now keeping validated offload configurations if conversion rate update fails.
- Imported SPI_OFFLOAD name space.
- Replaced DIV_ROUND_UP() by div_u64() to mitigate config check fail due to
  different integer rounding.
- When applicable, return early from regulator setup.
- Separate macros for offload and non-offload channels.
- Moved ltc2378_prepare_offload_message() downwards in source code.
- Wrapped transfer buffer declaration comment closer to 80 characters.
- Picked up review tags.

With best regards,
Marcelo


Marcelo Schmitt (4):
  dt-bindings: iio: adc: Add ltc2378
  iio: adc: ltc2378: Add support for LTC2378-20 and similar ADCs
  iio: adc: ltc2378: Enable high-speed data capture
  iio: adc: ltc2378: Enable triggered buffer data capture

 .../bindings/iio/adc/adi,ltc2378.yaml         | 170 ++++
 MAINTAINERS                                   |   8 +
 drivers/iio/adc/Kconfig                       |  19 +
 drivers/iio/adc/Makefile                      |   1 +
 drivers/iio/adc/ltc2378.c                     | 842 ++++++++++++++++++
 5 files changed, 1040 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/iio/adc/adi,ltc2378.yaml
 create mode 100644 drivers/iio/adc/ltc2378.c


base-commit: aa58ecc73466d0cb8c418de98e2225490bf600e3
-- 
2.53.0

[PATCH v7 1/4] dt-bindings: iio: adc: Add ltc2378

[Marcelo Schmitt]

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

Reviewed-by: David Lechner <dlechner@baylibre.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Marcelo Schmitt <marcelo.schmitt@analog.com>
---
Change log v6 -> v7:
No changes in v7.

 .../bindings/iio/adc/adi,ltc2378.yaml         | 170 ++++++++++++++++++
 MAINTAINERS                                   |   7 +
 2 files changed, 177 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/iio/adc/adi,ltc2378.yaml

diff --git a/Documentation/devicetree/bindings/iio/adc/adi,ltc2378.yaml b/Documentation/devicetree/bindings/iio/adc/adi,ltc2378.yaml
new file mode 100644
index 000000000000..33de1dc4c256
--- /dev/null
+++ b/Documentation/devicetree/bindings/iio/adc/adi,ltc2378.yaml
@@ -0,0 +1,170 @@
+# 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 <marcelo.schmitt@analog.com>
+
+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:
+      # Single compatible string match.
+      - enum:
+          - adi,ltc2338-18
+          - adi,ltc2364-16
+          - adi,ltc2364-18
+          - adi,ltc2376-16
+          - adi,ltc2376-18
+          - adi,ltc2376-20
+
+      # Low sample rate fallback for 16-bit unipolar sensors.
+      - items:
+          - enum:
+              - adi,ltc2370-16 # 2 MSPS
+              - adi,ltc2368-16 # 1 MSPS
+              - adi,ltc2367-16 # 500 kSPS
+          - const: adi,ltc2364-16 # fallback (250 kSPS)
+
+      # Low sample rate fallback for 18-bit unipolar sensors.
+      - items:
+          - enum:
+              - adi,ltc2369-18 # 1.6 MSPS
+              - adi,ltc2368-18 # 1 MSPS
+              - adi,ltc2367-18 # 500 kSPS
+          - const: adi,ltc2364-18 # fallback (250 kSPS)
+
+      # Low sample rate fallback for 16-bit bipolar sensors.
+      - items:
+          - enum:
+              - adi,ltc2380-16 # 2 MSPS
+              - adi,ltc2378-16 # 1 MSPS
+              - adi,ltc2377-16 # 500 kSPS
+          - const: adi,ltc2376-16 # fallback (250 kSPS)
+
+      # Low sample rate fallback for 18-bit bipolar sensors.
+      - items:
+          - enum:
+              - adi,ltc2379-18 # 1.6 MSPS
+              - adi,ltc2378-18 # 1 MSPS
+              - adi,ltc2377-18 # 500 kSPS
+          - const: adi,ltc2376-18 # fallback (250 kSPS)
+
+      # Low sample rate fallback for 20-bit bipolar sensors.
+      - items:
+          - enum:
+              - adi,ltc2378-20 # 1 MSPS
+              - adi,ltc2377-20 # 500 kSPS
+          - const: adi,ltc2376-20 # fallback (250 kSPS)
+
+  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:
+      Voltage reference input that determines the scale of ADC conversions.
+
+  refin-supply:
+    description:
+      Alternative voltage reference input.
+
+  cnv-gpios:
+    description:
+      When provided, this property indicates the GPIO that is connected to the
+      CNV pin.
+    maxItems: 1
+
+  pwms:
+    description: PWM signal 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.
+    maxItems: 1
+
+required:
+  - compatible
+  - reg
+  - vdd-supply
+  - ovdd-supply
+
+allOf:
+  # Except for LTC2338, all designs require a voltage reference input
+  - if:
+      properties:
+        compatible:
+          not:
+            contains:
+              enum:
+                - adi,ltc2338-18
+    then:
+      required:
+        - ref-supply
+      properties:
+        refin-supply: false
+    else:
+      properties:
+        ref-supply: false
+
+unevaluatedProperties: false
+
+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", "adi,ltc2376-20";
+            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>;
+        };
+    };
diff --git a/MAINTAINERS b/MAINTAINERS
index 2b1ec46c5919..f0ae26699c99 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -15343,6 +15343,13 @@ S:	Maintained
 F:	Documentation/devicetree/bindings/iio/dac/lltc,ltc1660.yaml
 F:	drivers/iio/dac/ltc1660.c
 
+LTC2378 IIO ADC DRIVER
+M:	Marcelo Schmitt <marcelo.schmitt@analog.com>
+L:	linux-iio@vger.kernel.org
+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 <michael.hennerich@analog.com>
 M:	Kim Seer Paller <kimseer.paller@analog.com>
-- 
2.53.0

[PATCH v7 2/4] iio: adc: ltc2378: Add support for LTC2378-20 and similar ADCs

[Marcelo Schmitt]

Support for LTC2378-20 and similar analog-to-digital converters.

Reviewed-by: David Lechner <dlechner@baylibre.com>
Signed-off-by: Marcelo Schmitt <marcelo.schmitt@analog.com>
---
Change log v6 -> v7:
- Extended single-read critical section scope (holding mutex lock longer).
- Added comment about conversion wait time.
- When applicable, return early from regulator setup.
- Wrapped transfer buffer declaration comment closer to 80 characters.

Some bits related to the SPI transfer buffer are introduced early to minimize
the change diff of the followup offload enablement patch.

 MAINTAINERS               |   1 +
 drivers/iio/adc/Kconfig   |  12 ++
 drivers/iio/adc/Makefile  |   1 +
 drivers/iio/adc/ltc2378.c | 416 ++++++++++++++++++++++++++++++++++++++
 4 files changed, 430 insertions(+)
 create mode 100644 drivers/iio/adc/ltc2378.c

diff --git a/MAINTAINERS b/MAINTAINERS
index f0ae26699c99..25821b771692 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -15349,6 +15349,7 @@ L:	linux-iio@vger.kernel.org
 S:	Supported
 W:	https://ez.analog.com/linux-software-drivers
 F:	Documentation/devicetree/bindings/iio/adc/adi,ltc2378.yaml
+F:	drivers/iio/adc/ltc2378.c
 
 LTC2664 IIO DAC DRIVER
 M:	Michael Hennerich <michael.hennerich@analog.com>
diff --git a/drivers/iio/adc/Kconfig b/drivers/iio/adc/Kconfig
index d1b198cb8a80..220c6739a8f2 100644
--- a/drivers/iio/adc/Kconfig
+++ b/drivers/iio/adc/Kconfig
@@ -943,6 +943,18 @@ config LTC2309
 	  This driver can also be built as a module. If so, the module will
 	  be called ltc2309.
 
+config LTC2378
+	tristate "Analog Devices LTC2378 ADC driver"
+	depends on SPI
+	depends on REGULATOR || COMPILE_TEST
+	depends on GPIOLIB
+	help
+	  Say yes here to build support for Analog Devices LTC2378-20 and
+	  similar analog to digital converters.
+
+	  This driver can also be built as a module. If so, the module will
+	  be called ltc2378.
+
 config LTC2471
 	tristate "Linear Technology LTC2471 and LTC2473 ADC driver"
 	depends on I2C
diff --git a/drivers/iio/adc/Makefile b/drivers/iio/adc/Makefile
index 0f90b75577ff..6058a8be6ccd 100644
--- a/drivers/iio/adc/Makefile
+++ b/drivers/iio/adc/Makefile
@@ -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
diff --git a/drivers/iio/adc/ltc2378.c b/drivers/iio/adc/ltc2378.c
new file mode 100644
index 000000000000..5600c820c7f4
--- /dev/null
+++ b/drivers/iio/adc/ltc2378.c
@@ -0,0 +1,416 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Analog Devices LTC2378 ADC series driver
+ *
+ * Copyright (C) 2026 Analog Devices Inc.
+ * Author: Marcelo Schmitt <marcelo.schmitt@analog.com>
+ */
+
+#include <linux/bitops.h>
+#include <linux/bits.h>
+#include <linux/byteorder/generic.h>
+#include <linux/cleanup.h>
+#include <linux/device.h>
+#include <linux/delay.h>
+#include <linux/device-id/spi.h>
+#include <linux/device-id/of.h>
+#include <linux/err.h>
+#include <linux/gpio/consumer.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/regulator/consumer.h>
+#include <linux/spi/spi.h>
+#include <linux/types.h>
+#include <linux/units.h>
+
+#include <linux/iio/iio.h>
+#include <linux/iio/types.h>
+
+#define LTC2378_MAX_DATA_WAIT_US	4 /* max(TBUSYLH + TCONV + TDSDOBUSYL) */
+
+#define LTC2378_DIFF_CHANNEL(_sign, _real_bits, _storage_bits)			\
+{										\
+	.type = IIO_VOLTAGE,							\
+	.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |				\
+			      BIT(IIO_CHAN_INFO_SCALE),				\
+	.scan_index = 0,							\
+	.scan_type = {								\
+		.format = _sign ? IIO_SCAN_FORMAT_SIGNED_INT :			\
+				  IIO_SCAN_FORMAT_UNSIGNED_INT,			\
+		.realbits = _real_bits,						\
+		.storagebits = _storage_bits,					\
+		.shift = _storage_bits - _real_bits,				\
+		.endianness = IIO_BE,						\
+	},									\
+}
+
+#define LTC2378_BIPOLAR_DIFF_CHANNEL(_real_bits)				\
+	LTC2378_DIFF_CHANNEL(1, _real_bits, (((_real_bits) > 16) ? 32 : 16))
+
+#define LTC2378_UNIPOLAR_DIFF_CHANNEL(_real_bits)				\
+	LTC2378_DIFF_CHANNEL(0, _real_bits, (((_real_bits) > 16) ? 32 : 16))
+
+struct ltc2378_chip_info {
+	const char *name;
+	unsigned int internal_ref_uV;
+	struct iio_chan_spec chan;
+};
+
+struct ltc2378_state {
+	const struct ltc2378_chip_info *info;
+	struct gpio_desc *cnv_gpio;
+	struct spi_device *spi;
+	struct mutex lock; /* Protect data acquisition cycle */
+	int ref_uV;
+	struct spi_transfer xfer;
+
+	/*
+	 * 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);
+};
+
+static const struct ltc2378_chip_info ltc2338_18_chip_info = {
+	.name = "ltc2338-18",
+	.internal_ref_uV = 2048000,
+	.chan = LTC2378_BIPOLAR_DIFF_CHANNEL(18),
+};
+
+static const struct ltc2378_chip_info ltc2364_16_chip_info = {
+	.name = "ltc2364-16",
+	.chan = LTC2378_UNIPOLAR_DIFF_CHANNEL(16),
+};
+
+static const struct ltc2378_chip_info ltc2364_18_chip_info = {
+	.name = "ltc2364-18",
+	.chan = LTC2378_UNIPOLAR_DIFF_CHANNEL(18),
+};
+
+static const struct ltc2378_chip_info ltc2367_16_chip_info = {
+	.name = "ltc2367-16",
+	.chan = LTC2378_UNIPOLAR_DIFF_CHANNEL(16),
+};
+
+static const struct ltc2378_chip_info ltc2367_18_chip_info = {
+	.name = "ltc2367-18",
+	.chan = LTC2378_UNIPOLAR_DIFF_CHANNEL(18),
+};
+
+static const struct ltc2378_chip_info ltc2368_16_chip_info = {
+	.name = "ltc2368-16",
+	.chan = LTC2378_UNIPOLAR_DIFF_CHANNEL(16),
+};
+
+static const struct ltc2378_chip_info ltc2368_18_chip_info = {
+	.name = "ltc2368-18",
+	.chan = LTC2378_UNIPOLAR_DIFF_CHANNEL(18),
+};
+
+static const struct ltc2378_chip_info ltc2369_18_chip_info = {
+	.name = "ltc2369-18",
+	.chan = LTC2378_UNIPOLAR_DIFF_CHANNEL(18),
+};
+
+static const struct ltc2378_chip_info ltc2370_16_chip_info = {
+	.name = "ltc2370-16",
+	.chan = LTC2378_UNIPOLAR_DIFF_CHANNEL(16),
+};
+
+static const struct ltc2378_chip_info ltc2376_16_chip_info = {
+	.name = "ltc2376-16",
+	.chan = LTC2378_BIPOLAR_DIFF_CHANNEL(16),
+};
+
+static const struct ltc2378_chip_info ltc2376_18_chip_info = {
+	.name = "ltc2376-18",
+	.chan = LTC2378_BIPOLAR_DIFF_CHANNEL(18),
+};
+
+static const struct ltc2378_chip_info ltc2376_20_chip_info = {
+	.name = "ltc2376-20",
+	.chan = LTC2378_BIPOLAR_DIFF_CHANNEL(20),
+};
+
+static const struct ltc2378_chip_info ltc2377_16_chip_info = {
+	.name = "ltc2377-16",
+	.chan = LTC2378_BIPOLAR_DIFF_CHANNEL(16),
+};
+
+static const struct ltc2378_chip_info ltc2377_18_chip_info = {
+	.name = "ltc2377-18",
+	.chan = LTC2378_BIPOLAR_DIFF_CHANNEL(18),
+};
+
+static const struct ltc2378_chip_info ltc2377_20_chip_info = {
+	.name = "ltc2377-20",
+	.chan = LTC2378_BIPOLAR_DIFF_CHANNEL(20),
+};
+
+static const struct ltc2378_chip_info ltc2378_16_chip_info = {
+	.name = "ltc2378-16",
+	.chan = LTC2378_BIPOLAR_DIFF_CHANNEL(16),
+};
+
+static const struct ltc2378_chip_info ltc2378_18_chip_info = {
+	.name = "ltc2378-18",
+	.chan = LTC2378_BIPOLAR_DIFF_CHANNEL(18),
+};
+
+static const struct ltc2378_chip_info ltc2378_20_chip_info = {
+	.name = "ltc2378-20",
+	.chan = LTC2378_BIPOLAR_DIFF_CHANNEL(20),
+};
+
+static const struct ltc2378_chip_info ltc2379_18_chip_info = {
+	.name = "ltc2379-18",
+	.chan = LTC2378_BIPOLAR_DIFF_CHANNEL(18),
+};
+
+static const struct ltc2378_chip_info ltc2380_16_chip_info = {
+	.name = "ltc2380-16",
+	.chan = LTC2378_BIPOLAR_DIFF_CHANNEL(16),
+};
+
+static int ltc2378_convert_and_acquire(struct ltc2378_state *st)
+{
+	int ret;
+
+	/* Cause a rising edge of CNV to initiate a new ADC conversion */
+	gpiod_set_value_cansleep(st->cnv_gpio, 1);
+	fsleep(LTC2378_MAX_DATA_WAIT_US);
+	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)
+{
+	const struct iio_scan_type *scan_type = &chan->scan_type;
+	u32 sample;
+	int ret;
+
+	guard(mutex)(&st->lock);
+	ret = ltc2378_convert_and_acquire(st);
+	if (ret)
+		return ret;
+
+	if (chan->scan_type.endianness == IIO_BE) {
+		if (chan->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 { /* IIO_CPU */
+		if (chan->scan_type.realbits > 16)
+			sample = st->scan.data.sample_buf32;
+		else
+			sample = st->scan.data.sample_buf16;
+	}
+
+	sample >>= chan->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;
+}
+
+static int ltc2378_read_raw(struct iio_dev *indio_dev,
+			    const struct iio_chan_spec *chan,
+			    int *val, int *val2, long mask)
+{
+	struct ltc2378_state *st = iio_priv(indio_dev);
+	int ret;
+
+	switch (mask) {
+	case IIO_CHAN_INFO_RAW: {
+		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 polarity / output code format:
+		 * - straight binary: All precision/resolution bits are used.
+		 * - 2's complement: One of the precision bits is used for sign.
+		 */
+		if (chan->scan_type.format == IIO_SCAN_FORMAT_SIGNED_INT)
+			*val2 = chan->scan_type.realbits - 1;
+		else
+			*val2 = chan->scan_type.realbits;
+
+		return IIO_VAL_FRACTIONAL_LOG2;
+
+	default:
+		return -EINVAL;
+	}
+}
+
+static const struct iio_info ltc2378_iio_info = {
+	.read_raw = &ltc2378_read_raw,
+};
+
+static int ltc2378_refin_setup(struct device *dev, struct ltc2378_state *st)
+{
+	int ret;
+
+	/*
+	 * The internal reference buffer amplifies both the internal reference
+	 * and REFIN by a factor of 2.
+	 */
+	ret = devm_regulator_get_enable_read_voltage(dev, "refin");
+	if (ret == -ENODEV) { /* refin is optional */
+		st->ref_uV = st->info->internal_ref_uV * 2;
+		return 0;
+	} else if (ret < 0) {
+		return dev_err_probe(dev, ret, "failed to read refin regulator\n");
+	}
+
+	st->ref_uV = ret * 2;
+
+	return 0;
+}
+
+static int ltc2378_ref_setup(struct device *dev, struct ltc2378_state *st)
+{
+	int ret;
+
+	ret = devm_regulator_get_enable_read_voltage(dev, "ref");
+	if (ret < 0)
+		return dev_err_probe(dev, ret, "failed to read ref regulator\n");
+
+	st->ref_uV = ret;
+
+	return 0;
+}
+
+static int ltc2378_probe(struct spi_device *spi)
+{
+	struct device *dev = &spi->dev;
+	struct iio_dev *indio_dev;
+	struct ltc2378_state *st;
+	int ret;
+
+	indio_dev = devm_iio_device_alloc(&spi->dev, sizeof(*st));
+	if (!indio_dev)
+		return -ENOMEM;
+
+	st = iio_priv(indio_dev);
+	st->spi = spi;
+
+	ret = devm_mutex_init(dev, &st->lock);
+	if (ret)
+		return ret;
+
+	st->info = spi_get_device_match_data(spi);
+	if (!st->info)
+		return -EINVAL;
+
+	if (st->info->internal_ref_uV)
+		ret = ltc2378_refin_setup(dev, st);
+	else
+		ret = ltc2378_ref_setup(dev, st);
+	if (ret)
+		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);
+	if (IS_ERR(st->cnv_gpio))
+		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->xfer.rx_buf = &st->scan.data;
+	st->xfer.len = spi_bpw_to_bytes(indio_dev->channels[0].scan_type.realbits);
+
+	return devm_iio_device_register(&spi->dev, indio_dev);
+}
+
+static const struct of_device_id ltc2378_of_match[] = {
+	{ .compatible = "adi,ltc2338-18", .data = &ltc2338_18_chip_info },
+	{ .compatible = "adi,ltc2364-16", .data = &ltc2364_16_chip_info },
+	{ .compatible = "adi,ltc2364-18", .data = &ltc2364_18_chip_info },
+	{ .compatible = "adi,ltc2367-16", .data = &ltc2367_16_chip_info },
+	{ .compatible = "adi,ltc2367-18", .data = &ltc2367_18_chip_info },
+	{ .compatible = "adi,ltc2368-16", .data = &ltc2368_16_chip_info },
+	{ .compatible = "adi,ltc2368-18", .data = &ltc2368_18_chip_info },
+	{ .compatible = "adi,ltc2369-18", .data = &ltc2369_18_chip_info },
+	{ .compatible = "adi,ltc2370-16", .data = &ltc2370_16_chip_info },
+	{ .compatible = "adi,ltc2376-16", .data = &ltc2376_16_chip_info },
+	{ .compatible = "adi,ltc2376-18", .data = &ltc2376_18_chip_info },
+	{ .compatible = "adi,ltc2376-20", .data = &ltc2376_20_chip_info },
+	{ .compatible = "adi,ltc2377-16", .data = &ltc2377_16_chip_info },
+	{ .compatible = "adi,ltc2377-18", .data = &ltc2377_18_chip_info },
+	{ .compatible = "adi,ltc2377-20", .data = &ltc2377_20_chip_info },
+	{ .compatible = "adi,ltc2378-16", .data = &ltc2378_16_chip_info },
+	{ .compatible = "adi,ltc2378-18", .data = &ltc2378_18_chip_info },
+	{ .compatible = "adi,ltc2378-20", .data = &ltc2378_20_chip_info },
+	{ .compatible = "adi,ltc2379-18", .data = &ltc2379_18_chip_info },
+	{ .compatible = "adi,ltc2380-16", .data = &ltc2380_16_chip_info },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, ltc2378_of_match);
+
+static const struct spi_device_id ltc2378_spi_id[] = {
+	{ .name = "ltc2338-18", .driver_data = (kernel_ulong_t)&ltc2338_18_chip_info },
+	{ .name = "ltc2364-16", .driver_data = (kernel_ulong_t)&ltc2364_16_chip_info },
+	{ .name = "ltc2364-18", .driver_data = (kernel_ulong_t)&ltc2364_18_chip_info },
+	{ .name = "ltc2367-16", .driver_data = (kernel_ulong_t)&ltc2367_16_chip_info },
+	{ .name = "ltc2367-18", .driver_data = (kernel_ulong_t)&ltc2367_18_chip_info },
+	{ .name = "ltc2368-16", .driver_data = (kernel_ulong_t)&ltc2368_16_chip_info },
+	{ .name = "ltc2368-18", .driver_data = (kernel_ulong_t)&ltc2368_18_chip_info },
+	{ .name = "ltc2369-18", .driver_data = (kernel_ulong_t)&ltc2369_18_chip_info },
+	{ .name = "ltc2370-16", .driver_data = (kernel_ulong_t)&ltc2370_16_chip_info },
+	{ .name = "ltc2376-16", .driver_data = (kernel_ulong_t)&ltc2376_16_chip_info },
+	{ .name = "ltc2376-18", .driver_data = (kernel_ulong_t)&ltc2376_18_chip_info },
+	{ .name = "ltc2376-20", .driver_data = (kernel_ulong_t)&ltc2376_20_chip_info },
+	{ .name = "ltc2377-16", .driver_data = (kernel_ulong_t)&ltc2377_16_chip_info },
+	{ .name = "ltc2377-18", .driver_data = (kernel_ulong_t)&ltc2377_18_chip_info },
+	{ .name = "ltc2377-20", .driver_data = (kernel_ulong_t)&ltc2377_20_chip_info },
+	{ .name = "ltc2378-16", .driver_data = (kernel_ulong_t)&ltc2378_16_chip_info },
+	{ .name = "ltc2378-18", .driver_data = (kernel_ulong_t)&ltc2378_18_chip_info },
+	{ .name = "ltc2378-20", .driver_data = (kernel_ulong_t)&ltc2378_20_chip_info },
+	{ .name = "ltc2379-18", .driver_data = (kernel_ulong_t)&ltc2379_18_chip_info },
+	{ .name = "ltc2380-16", .driver_data = (kernel_ulong_t)&ltc2380_16_chip_info },
+	{ }
+};
+MODULE_DEVICE_TABLE(spi, ltc2378_spi_id);
+
+static struct spi_driver ltc2378_driver = {
+	.driver = {
+		.name = "ltc2378",
+		.of_match_table = ltc2378_of_match
+	},
+	.probe = ltc2378_probe,
+	.id_table = ltc2378_spi_id,
+};
+module_spi_driver(ltc2378_driver);
+
+MODULE_AUTHOR("Marcelo Schmitt <marcelo.schmitt@analog.com>");
+MODULE_DESCRIPTION("Analog Devices LTC2378 ADC series driver");
+MODULE_LICENSE("GPL");
-- 
2.53.0

[PATCH v7 3/4] iio: adc: ltc2378: Enable high-speed data capture

[Marcelo Schmitt]

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

Reviewed-by: David Lechner <dlechner@baylibre.com>
Signed-off-by: Marcelo Schmitt <marcelo.schmitt@analog.com>
---
Change log v6 -> v7:
- Now keeping validated offload configurations if conversion rate update fails.
- Imported SPI_OFFLOAD name space.
- Replaced DIV_ROUND_UP() by div_u64() to mitigate config check fail due to
  different integer rounding.
- Separate macros for offload and non-offload channels.
- Moved ltc2378_prepare_offload_message() downwards in source code.

 drivers/iio/adc/Kconfig   |   6 +
 drivers/iio/adc/ltc2378.c | 403 +++++++++++++++++++++++++++++++++++++-
 2 files changed, 406 insertions(+), 3 deletions(-)

diff --git a/drivers/iio/adc/Kconfig b/drivers/iio/adc/Kconfig
index 220c6739a8f2..96df8453b826 100644
--- a/drivers/iio/adc/Kconfig
+++ b/drivers/iio/adc/Kconfig
@@ -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.
diff --git a/drivers/iio/adc/ltc2378.c b/drivers/iio/adc/ltc2378.c
index 5600c820c7f4..7d29f021cb7b 100644
--- a/drivers/iio/adc/ltc2378.c
+++ b/drivers/iio/adc/ltc2378.c
@@ -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_DIFF_CHANNEL(_sign, _real_bits, _storage_bits)			\
@@ -50,10 +61,46 @@
 #define LTC2378_UNIPOLAR_DIFF_CHANNEL(_real_bits)				\
 	LTC2378_DIFF_CHANNEL(0, _real_bits, (((_real_bits) > 16) ? 32 : 16))
 
+#define LTC2378_DIFF_CHANNEL_OFFLOAD(_sign, _real_bits, _storage_bits)		\
+{										\
+	.type = IIO_VOLTAGE,							\
+	.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_BIPOLAR_DIFF_CHANNEL(_real_bits)			\
+	LTC2378_DIFF_CHANNEL_OFFLOAD(1, (_real_bits), 32)
+
+#define LTC2378_OFFLOAD_UNIPOLAR_DIFF_CHANNEL(_real_bits)			\
+	LTC2378_DIFF_CHANNEL_OFFLOAD(0, (_real_bits), 32)
+
 struct ltc2378_chip_info {
 	const char *name;
 	unsigned int internal_ref_uV;
 	struct iio_chan_spec chan;
+	struct iio_chan_spec offload_chan;
+	unsigned int max_sample_rate_Hz;
+	unsigned int tconv_ns;
 };
 
 struct ltc2378_state {
@@ -63,6 +110,15 @@ 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
@@ -83,101 +139,161 @@ static const struct ltc2378_chip_info ltc2338_18_chip_info = {
 	.name = "ltc2338-18",
 	.internal_ref_uV = 2048000,
 	.chan = LTC2378_BIPOLAR_DIFF_CHANNEL(18),
+	.offload_chan = LTC2378_OFFLOAD_BIPOLAR_DIFF_CHANNEL(18),
+	.max_sample_rate_Hz = 1 * HZ_PER_MHZ,
+	.tconv_ns = 527,
 };
 
 static const struct ltc2378_chip_info ltc2364_16_chip_info = {
 	.name = "ltc2364-16",
 	.chan = LTC2378_UNIPOLAR_DIFF_CHANNEL(16),
+	.offload_chan = LTC2378_OFFLOAD_UNIPOLAR_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_UNIPOLAR_DIFF_CHANNEL(18),
+	.offload_chan = LTC2378_OFFLOAD_UNIPOLAR_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_UNIPOLAR_DIFF_CHANNEL(16),
+	.offload_chan = LTC2378_OFFLOAD_UNIPOLAR_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_UNIPOLAR_DIFF_CHANNEL(18),
+	.offload_chan = LTC2378_OFFLOAD_UNIPOLAR_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_UNIPOLAR_DIFF_CHANNEL(16),
+	.offload_chan = LTC2378_OFFLOAD_UNIPOLAR_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_UNIPOLAR_DIFF_CHANNEL(18),
+	.offload_chan = LTC2378_OFFLOAD_UNIPOLAR_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_UNIPOLAR_DIFF_CHANNEL(18),
+	.offload_chan = LTC2378_OFFLOAD_UNIPOLAR_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_UNIPOLAR_DIFF_CHANNEL(16),
+	.offload_chan = LTC2378_OFFLOAD_UNIPOLAR_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_BIPOLAR_DIFF_CHANNEL(16),
+	.offload_chan = LTC2378_OFFLOAD_BIPOLAR_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_BIPOLAR_DIFF_CHANNEL(18),
+	.offload_chan = LTC2378_OFFLOAD_BIPOLAR_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_BIPOLAR_DIFF_CHANNEL(20),
+	.offload_chan = LTC2378_OFFLOAD_BIPOLAR_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_BIPOLAR_DIFF_CHANNEL(16),
+	.offload_chan = LTC2378_OFFLOAD_BIPOLAR_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_BIPOLAR_DIFF_CHANNEL(18),
+	.offload_chan = LTC2378_OFFLOAD_BIPOLAR_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_BIPOLAR_DIFF_CHANNEL(20),
+	.offload_chan = LTC2378_OFFLOAD_BIPOLAR_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_BIPOLAR_DIFF_CHANNEL(16),
+	.offload_chan = LTC2378_OFFLOAD_BIPOLAR_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_BIPOLAR_DIFF_CHANNEL(18),
+	.offload_chan = LTC2378_OFFLOAD_BIPOLAR_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_BIPOLAR_DIFF_CHANNEL(20),
+	.offload_chan = LTC2378_OFFLOAD_BIPOLAR_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_BIPOLAR_DIFF_CHANNEL(18),
+	.offload_chan = LTC2378_OFFLOAD_BIPOLAR_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_BIPOLAR_DIFF_CHANNEL(16),
+	.offload_chan = LTC2378_OFFLOAD_BIPOLAR_DIFF_CHANNEL(16),
+	.max_sample_rate_Hz = 2 * HZ_PER_MHZ,
+	.tconv_ns = 322,
 };
 
 static int ltc2378_convert_and_acquire(struct ltc2378_state *st)
@@ -260,7 +376,137 @@ 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;
 	}
@@ -270,6 +516,111 @@ 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_refin_setup(struct device *dev, struct ltc2378_state *st)
 {
 	int ret;
@@ -334,7 +685,6 @@ 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);
@@ -342,8 +692,53 @@ 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);
@@ -414,3 +809,5 @@ 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");
-- 
2.53.0

[PATCH v7 4/4] iio: adc: ltc2378: Enable triggered buffer data capture

[Marcelo Schmitt]

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

Reviewed-by: David Lechner <dlechner@baylibre.com>
Signed-off-by: Marcelo Schmitt <marcelo.schmitt@analog.com>
---
Change log v6 -> v7:
No changes in v7.

 drivers/iio/adc/Kconfig   |  1 +
 drivers/iio/adc/ltc2378.c | 75 +++++++++++++++++++++++++++------------
 2 files changed, 53 insertions(+), 23 deletions(-)

diff --git a/drivers/iio/adc/Kconfig b/drivers/iio/adc/Kconfig
index 96df8453b826..6cf67f7a6eed 100644
--- a/drivers/iio/adc/Kconfig
+++ b/drivers/iio/adc/Kconfig
@@ -952,6 +952,7 @@ config LTC2378
 	select IIO_BUFFER
 	select IIO_BUFFER_DMA
 	select IIO_BUFFER_DMAENGINE
+	select IIO_TRIGGERED_BUFFER
 	select SPI_OFFLOAD
 	select SPI_OFFLOAD_TRIGGER_PWM
 	help
diff --git a/drivers/iio/adc/ltc2378.c b/drivers/iio/adc/ltc2378.c
index 7d29f021cb7b..25db69edee4d 100644
--- a/drivers/iio/adc/ltc2378.c
+++ b/drivers/iio/adc/ltc2378.c
@@ -6,6 +6,7 @@
  * Author: Marcelo Schmitt <marcelo.schmitt@analog.com>
  */
 
+#include <linux/array_size.h>
 #include <linux/bitops.h>
 #include <linux/bits.h>
 #include <linux/byteorder/generic.h>
@@ -32,6 +33,8 @@
 #include <linux/iio/buffer.h>
 #include <linux/iio/buffer-dmaengine.h>
 #include <linux/iio/iio.h>
+#include <linux/iio/triggered_buffer.h>
+#include <linux/iio/trigger_consumer.h>
 #include <linux/iio/types.h>
 
 #define LTC2378_TDSDOBUSYL_NS		5
@@ -97,7 +100,7 @@
 struct ltc2378_chip_info {
 	const char *name;
 	unsigned int internal_ref_uV;
-	struct iio_chan_spec chan;
+	struct iio_chan_spec chan[2]; /* 1 physical chan + 1 timestamp chan */
 	struct iio_chan_spec offload_chan;
 	unsigned int max_sample_rate_Hz;
 	unsigned int tconv_ns;
@@ -138,7 +141,7 @@ struct ltc2378_state {
 static const struct ltc2378_chip_info ltc2338_18_chip_info = {
 	.name = "ltc2338-18",
 	.internal_ref_uV = 2048000,
-	.chan = LTC2378_BIPOLAR_DIFF_CHANNEL(18),
+	.chan = { LTC2378_BIPOLAR_DIFF_CHANNEL(18), IIO_CHAN_SOFT_TIMESTAMP(1) },
 	.offload_chan = LTC2378_OFFLOAD_BIPOLAR_DIFF_CHANNEL(18),
 	.max_sample_rate_Hz = 1 * HZ_PER_MHZ,
 	.tconv_ns = 527,
@@ -146,7 +149,7 @@ static const struct ltc2378_chip_info ltc2338_18_chip_info = {
 
 static const struct ltc2378_chip_info ltc2364_16_chip_info = {
 	.name = "ltc2364-16",
-	.chan = LTC2378_UNIPOLAR_DIFF_CHANNEL(16),
+	.chan = { LTC2378_UNIPOLAR_DIFF_CHANNEL(16), IIO_CHAN_SOFT_TIMESTAMP(1) },
 	.offload_chan = LTC2378_OFFLOAD_UNIPOLAR_DIFF_CHANNEL(16),
 	.max_sample_rate_Hz = 250 * HZ_PER_KHZ,
 	.tconv_ns = 3000,
@@ -154,7 +157,7 @@ static const struct ltc2378_chip_info ltc2364_16_chip_info = {
 
 static const struct ltc2378_chip_info ltc2364_18_chip_info = {
 	.name = "ltc2364-18",
-	.chan = LTC2378_UNIPOLAR_DIFF_CHANNEL(18),
+	.chan = { LTC2378_UNIPOLAR_DIFF_CHANNEL(18), IIO_CHAN_SOFT_TIMESTAMP(1) },
 	.offload_chan = LTC2378_OFFLOAD_UNIPOLAR_DIFF_CHANNEL(18),
 	.max_sample_rate_Hz = 250 * HZ_PER_KHZ,
 	.tconv_ns = 3000,
@@ -162,7 +165,7 @@ static const struct ltc2378_chip_info ltc2364_18_chip_info = {
 
 static const struct ltc2378_chip_info ltc2367_16_chip_info = {
 	.name = "ltc2367-16",
-	.chan = LTC2378_UNIPOLAR_DIFF_CHANNEL(16),
+	.chan = { LTC2378_UNIPOLAR_DIFF_CHANNEL(16), IIO_CHAN_SOFT_TIMESTAMP(1) },
 	.offload_chan = LTC2378_OFFLOAD_UNIPOLAR_DIFF_CHANNEL(16),
 	.max_sample_rate_Hz = 500 * HZ_PER_KHZ,
 	.tconv_ns = 1500,
@@ -170,7 +173,7 @@ static const struct ltc2378_chip_info ltc2367_16_chip_info = {
 
 static const struct ltc2378_chip_info ltc2367_18_chip_info = {
 	.name = "ltc2367-18",
-	.chan = LTC2378_UNIPOLAR_DIFF_CHANNEL(18),
+	.chan = { LTC2378_UNIPOLAR_DIFF_CHANNEL(18), IIO_CHAN_SOFT_TIMESTAMP(1) },
 	.offload_chan = LTC2378_OFFLOAD_UNIPOLAR_DIFF_CHANNEL(18),
 	.max_sample_rate_Hz = 500 * HZ_PER_KHZ,
 	.tconv_ns = 1500,
@@ -178,7 +181,7 @@ static const struct ltc2378_chip_info ltc2367_18_chip_info = {
 
 static const struct ltc2378_chip_info ltc2368_16_chip_info = {
 	.name = "ltc2368-16",
-	.chan = LTC2378_UNIPOLAR_DIFF_CHANNEL(16),
+	.chan = { LTC2378_UNIPOLAR_DIFF_CHANNEL(16), IIO_CHAN_SOFT_TIMESTAMP(1) },
 	.offload_chan = LTC2378_OFFLOAD_UNIPOLAR_DIFF_CHANNEL(16),
 	.max_sample_rate_Hz = 1 * HZ_PER_MHZ,
 	.tconv_ns = 527,
@@ -186,7 +189,7 @@ static const struct ltc2378_chip_info ltc2368_16_chip_info = {
 
 static const struct ltc2378_chip_info ltc2368_18_chip_info = {
 	.name = "ltc2368-18",
-	.chan = LTC2378_UNIPOLAR_DIFF_CHANNEL(18),
+	.chan = { LTC2378_UNIPOLAR_DIFF_CHANNEL(18), IIO_CHAN_SOFT_TIMESTAMP(1) },
 	.offload_chan = LTC2378_OFFLOAD_UNIPOLAR_DIFF_CHANNEL(18),
 	.max_sample_rate_Hz = 1 * HZ_PER_MHZ,
 	.tconv_ns = 527,
@@ -194,7 +197,7 @@ static const struct ltc2378_chip_info ltc2368_18_chip_info = {
 
 static const struct ltc2378_chip_info ltc2369_18_chip_info = {
 	.name = "ltc2369-18",
-	.chan = LTC2378_UNIPOLAR_DIFF_CHANNEL(18),
+	.chan = { LTC2378_UNIPOLAR_DIFF_CHANNEL(18), IIO_CHAN_SOFT_TIMESTAMP(1) },
 	.offload_chan = LTC2378_OFFLOAD_UNIPOLAR_DIFF_CHANNEL(18),
 	.max_sample_rate_Hz = 1600 * HZ_PER_KHZ,
 	.tconv_ns = 412,
@@ -202,7 +205,7 @@ static const struct ltc2378_chip_info ltc2369_18_chip_info = {
 
 static const struct ltc2378_chip_info ltc2370_16_chip_info = {
 	.name = "ltc2370-16",
-	.chan = LTC2378_UNIPOLAR_DIFF_CHANNEL(16),
+	.chan = { LTC2378_UNIPOLAR_DIFF_CHANNEL(16), IIO_CHAN_SOFT_TIMESTAMP(1) },
 	.offload_chan = LTC2378_OFFLOAD_UNIPOLAR_DIFF_CHANNEL(16),
 	.max_sample_rate_Hz = 2 * HZ_PER_MHZ,
 	.tconv_ns = 322,
@@ -210,7 +213,7 @@ static const struct ltc2378_chip_info ltc2370_16_chip_info = {
 
 static const struct ltc2378_chip_info ltc2376_16_chip_info = {
 	.name = "ltc2376-16",
-	.chan = LTC2378_BIPOLAR_DIFF_CHANNEL(16),
+	.chan = { LTC2378_BIPOLAR_DIFF_CHANNEL(16), IIO_CHAN_SOFT_TIMESTAMP(1) },
 	.offload_chan = LTC2378_OFFLOAD_BIPOLAR_DIFF_CHANNEL(16),
 	.max_sample_rate_Hz = 250 * HZ_PER_KHZ,
 	.tconv_ns = 3000,
@@ -218,7 +221,7 @@ static const struct ltc2378_chip_info ltc2376_16_chip_info = {
 
 static const struct ltc2378_chip_info ltc2376_18_chip_info = {
 	.name = "ltc2376-18",
-	.chan = LTC2378_BIPOLAR_DIFF_CHANNEL(18),
+	.chan = { LTC2378_BIPOLAR_DIFF_CHANNEL(18), IIO_CHAN_SOFT_TIMESTAMP(1) },
 	.offload_chan = LTC2378_OFFLOAD_BIPOLAR_DIFF_CHANNEL(18),
 	.max_sample_rate_Hz = 250 * HZ_PER_KHZ,
 	.tconv_ns = 3000,
@@ -226,7 +229,7 @@ static const struct ltc2378_chip_info ltc2376_18_chip_info = {
 
 static const struct ltc2378_chip_info ltc2376_20_chip_info = {
 	.name = "ltc2376-20",
-	.chan = LTC2378_BIPOLAR_DIFF_CHANNEL(20),
+	.chan = { LTC2378_BIPOLAR_DIFF_CHANNEL(20), IIO_CHAN_SOFT_TIMESTAMP(1) },
 	.offload_chan = LTC2378_OFFLOAD_BIPOLAR_DIFF_CHANNEL(20),
 	.max_sample_rate_Hz = 250 * HZ_PER_KHZ,
 	.tconv_ns = 3000,
@@ -234,7 +237,7 @@ static const struct ltc2378_chip_info ltc2376_20_chip_info = {
 
 static const struct ltc2378_chip_info ltc2377_16_chip_info = {
 	.name = "ltc2377-16",
-	.chan = LTC2378_BIPOLAR_DIFF_CHANNEL(16),
+	.chan = { LTC2378_BIPOLAR_DIFF_CHANNEL(16), IIO_CHAN_SOFT_TIMESTAMP(1) },
 	.offload_chan = LTC2378_OFFLOAD_BIPOLAR_DIFF_CHANNEL(16),
 	.max_sample_rate_Hz = 500 * HZ_PER_KHZ,
 	.tconv_ns = 1500,
@@ -242,7 +245,7 @@ static const struct ltc2378_chip_info ltc2377_16_chip_info = {
 
 static const struct ltc2378_chip_info ltc2377_18_chip_info = {
 	.name = "ltc2377-18",
-	.chan = LTC2378_BIPOLAR_DIFF_CHANNEL(18),
+	.chan = { LTC2378_BIPOLAR_DIFF_CHANNEL(18), IIO_CHAN_SOFT_TIMESTAMP(1) },
 	.offload_chan = LTC2378_OFFLOAD_BIPOLAR_DIFF_CHANNEL(18),
 	.max_sample_rate_Hz = 500 * HZ_PER_KHZ,
 	.tconv_ns = 1500,
@@ -250,7 +253,7 @@ static const struct ltc2378_chip_info ltc2377_18_chip_info = {
 
 static const struct ltc2378_chip_info ltc2377_20_chip_info = {
 	.name = "ltc2377-20",
-	.chan = LTC2378_BIPOLAR_DIFF_CHANNEL(20),
+	.chan = { LTC2378_BIPOLAR_DIFF_CHANNEL(20), IIO_CHAN_SOFT_TIMESTAMP(1) },
 	.offload_chan = LTC2378_OFFLOAD_BIPOLAR_DIFF_CHANNEL(20),
 	.max_sample_rate_Hz = 500 * HZ_PER_KHZ,
 	.tconv_ns = 1500,
@@ -258,7 +261,7 @@ static const struct ltc2378_chip_info ltc2377_20_chip_info = {
 
 static const struct ltc2378_chip_info ltc2378_16_chip_info = {
 	.name = "ltc2378-16",
-	.chan = LTC2378_BIPOLAR_DIFF_CHANNEL(16),
+	.chan = { LTC2378_BIPOLAR_DIFF_CHANNEL(16), IIO_CHAN_SOFT_TIMESTAMP(1) },
 	.offload_chan = LTC2378_OFFLOAD_BIPOLAR_DIFF_CHANNEL(16),
 	.max_sample_rate_Hz = 1 * HZ_PER_MHZ,
 	.tconv_ns = 527,
@@ -266,7 +269,7 @@ static const struct ltc2378_chip_info ltc2378_16_chip_info = {
 
 static const struct ltc2378_chip_info ltc2378_18_chip_info = {
 	.name = "ltc2378-18",
-	.chan = LTC2378_BIPOLAR_DIFF_CHANNEL(18),
+	.chan = { LTC2378_BIPOLAR_DIFF_CHANNEL(18), IIO_CHAN_SOFT_TIMESTAMP(1) },
 	.offload_chan = LTC2378_OFFLOAD_BIPOLAR_DIFF_CHANNEL(18),
 	.max_sample_rate_Hz = 1 * HZ_PER_MHZ,
 	.tconv_ns = 527,
@@ -274,7 +277,7 @@ static const struct ltc2378_chip_info ltc2378_18_chip_info = {
 
 static const struct ltc2378_chip_info ltc2378_20_chip_info = {
 	.name = "ltc2378-20",
-	.chan = LTC2378_BIPOLAR_DIFF_CHANNEL(20),
+	.chan = { LTC2378_BIPOLAR_DIFF_CHANNEL(20), IIO_CHAN_SOFT_TIMESTAMP(1) },
 	.offload_chan = LTC2378_OFFLOAD_BIPOLAR_DIFF_CHANNEL(20),
 	.max_sample_rate_Hz = 1 * HZ_PER_MHZ,
 	.tconv_ns = 675,
@@ -282,7 +285,7 @@ static const struct ltc2378_chip_info ltc2378_20_chip_info = {
 
 static const struct ltc2378_chip_info ltc2379_18_chip_info = {
 	.name = "ltc2379-18",
-	.chan = LTC2378_BIPOLAR_DIFF_CHANNEL(18),
+	.chan = { LTC2378_BIPOLAR_DIFF_CHANNEL(18), IIO_CHAN_SOFT_TIMESTAMP(1) },
 	.offload_chan = LTC2378_OFFLOAD_BIPOLAR_DIFF_CHANNEL(18),
 	.max_sample_rate_Hz = 1600 * HZ_PER_KHZ,
 	.tconv_ns = 412,
@@ -290,7 +293,7 @@ static const struct ltc2378_chip_info ltc2379_18_chip_info = {
 
 static const struct ltc2378_chip_info ltc2380_16_chip_info = {
 	.name = "ltc2380-16",
-	.chan = LTC2378_BIPOLAR_DIFF_CHANNEL(16),
+	.chan = { LTC2378_BIPOLAR_DIFF_CHANNEL(16), IIO_CHAN_SOFT_TIMESTAMP(1) },
 	.offload_chan = LTC2378_OFFLOAD_BIPOLAR_DIFF_CHANNEL(16),
 	.max_sample_rate_Hz = 2 * HZ_PER_MHZ,
 	.tconv_ns = 322,
@@ -309,6 +312,25 @@ static int ltc2378_convert_and_acquire(struct ltc2378_state *st)
 	return ret;
 }
 
+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_channel_single_read(const struct iio_chan_spec *chan,
 				       struct ltc2378_state *st, int *val)
 {
@@ -697,8 +719,15 @@ static int ltc2378_probe(struct spi_device *spi)
 	/* 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;
+		indio_dev->channels = st->info->chan;
+		indio_dev->num_channels = ARRAY_SIZE(st->info->chan);
+
+		ret = devm_iio_triggered_buffer_setup(dev, indio_dev,
+						      iio_pollfunc_store_time,
+						      ltc2378_trigger_handler,
+						      NULL);
+		if (ret)
+			return ret;
 	} else if (ret) {
 		return dev_err_probe(dev, ret, "failed to get offload\n");
 	} else {
-- 
2.53.0

Re: [PATCH v7 3/4] iio: adc: ltc2378: Enable high-speed data capture

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] Integer divide-by-zero leading to kernel panic in `ltc2378_update_conversion_rate` when a sampling frequency of 1 Hz is requested and the PWM driver rounds the period length above 1 second.
--

--- Patch [3]: [PATCH v7 3/4] iio: adc: ltc2378: Enable high-speed data capture ---
commit ef54f2c79f2cac1649922032814adc7fcc5f9684
Author: Marcelo Schmitt <marcelo.schmitt@analog.com>
Subject: iio: adc: ltc2378: Enable high-speed data capture

This commit enables high-speed data capture for the ltc2378 ADC driver by
utilizing SPI transfer offloading. It allows data acquisition at faster sample
rates up to 2 MSPS.

> diff --git a/drivers/iio/adc/ltc2378.c b/drivers/iio/adc/ltc2378.c
> index 5600c820c7f45..7d29f021cb7b4 100644
> --- a/drivers/iio/adc/ltc2378.c
> +++ b/drivers/iio/adc/ltc2378.c

[ ... ]

> +	/*
> +	 * 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);

[Severity: High]
Could this result in a kernel panic due to an integer division by zero?

If a user writes 1 to the IIO in_voltage_sampling_frequency sysfs attribute,
ltc2378_update_conversion_rate() is called with freq_Hz = 1, and the initial
requested PWM period is calculated as 1,000,000,000 ns.

If the underlying hardware PWM driver rounds the period slightly upwards
(e.g., to 1,000,000,001 ns) during pwm_round_waveform_might_sleep() due to
clock granularity, offload_period_ns will exceed HZ_PER_GHZ.

This causes config.periodic.frequency_hz = div_u64(HZ_PER_GHZ, offload_period_ns)
to evaluate to 0.

When div64_u64(HZ_PER_GHZ, config.periodic.frequency_hz) is subsequently called,
it divides by zero.

> +	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;
> +}

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/cover.1784235595.git.marcelo.schmitt@analog.com?part=3

Re: [PATCH v7 2/4] iio: adc: ltc2378: Add support for LTC2378-20 and similar ADCs

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] The `LTC2378_DIFF_CHANNEL` macro defines an IIO channel that is intended to be differential but lacks the `.differential = 1`, `.indexed = 1`, `.channel = 0`, and `.channel2 = 1` attributes.
--

--- Patch [2]: [PATCH v7 2/4] iio: adc: ltc2378: Add support for LTC2378-20 and similar ADCs ---
commit 5710d5f25b45906977e2522567c1964b1d3219f8
Author: Marcelo Schmitt <marcelo.schmitt@analog.com>

iio: adc: ltc2378: Add support for LTC2378-20 and similar ADCs

This commit adds a new driver for the Analog Devices LTC2378-20 and
similar analog-to-digital converters.

> diff --git a/drivers/iio/adc/ltc2378.c b/drivers/iio/adc/ltc2378.c
> new file mode 100644
> index 0000000000000..5600c820c7f45
> --- /dev/null
> +++ b/drivers/iio/adc/ltc2378.c
> @@ -0,0 +1,416 @@
[ ... ]
> +#define LTC2378_DIFF_CHANNEL(_sign, _real_bits, _storage_bits)			\
> +{										\
> +	.type = IIO_VOLTAGE,							\
> +	.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |				\
> +			      BIT(IIO_CHAN_INFO_SCALE),				\
> +	.scan_index = 0,							\

[Severity: Medium]
Does this macro need to set .differential = 1, .indexed = 1, .channel = 0,
and .channel2 = 1? The name suggests these are differential channels, but
without these attributes, the IIO ABI will expose them as single-ended
(e.g., in_voltage_raw instead of in_voltage0-voltage1_raw).

> +	.scan_type = {								\
> +		.format = _sign ? IIO_SCAN_FORMAT_SIGNED_INT :			\
> +				  IIO_SCAN_FORMAT_UNSIGNED_INT,			\
> +		.realbits = _real_bits,						\
> +		.storagebits = _storage_bits,					\
> +		.shift = _storage_bits - _real_bits,				\
> +		.endianness = IIO_BE,						\
> +	},									\
> +}
> +
> +#define LTC2378_BIPOLAR_DIFF_CHANNEL(_real_bits)				\
> +	LTC2378_DIFF_CHANNEL(1, _real_bits, (((_real_bits) > 16) ? 32 : 16))
> +
> +#define LTC2378_UNIPOLAR_DIFF_CHANNEL(_real_bits)				\
> +	LTC2378_DIFF_CHANNEL(0, _real_bits, (((_real_bits) > 16) ? 32 : 16))
> +
[ ... ]

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/cover.1784235595.git.marcelo.schmitt@analog.com?part=2

Re: [PATCH v7 0/4] iio: adc: Add support for LTC2378 and similar ADCs

[Andy Shevchenko]

On Thu, Jul 16, 2026 at 06:08:49PM -0300, Marcelo Schmitt wrote:
> This patch series adds support for LTC2378 and similar low noise, low power,
> high speed, successive approximation register (SAR) ADCs. These ADCs are similar
> among each other, varying mainly on the amount of precision bits, maximum sample
> rate, and input configuration (either fully differential or pseudo-differential).
> 
> Patch 1 adds device tree documentation for LTC2378.
> 
> Patch 2 enables single-shot sample read with a GPIO connected to the LTC2378 CNV pin.
> 
> Patch 3 enables high-speed data captures with SPI offloading.
> The setup is similar to AD4030, with a specialized PWM generator being used both
> for SPI offload triggering and conversion start signaling.
> 
> Patch 4 enables running buffered data captures without SPI offloading.
> 
> Even though these parts are somewhat similar to AD4000, the wiring configuration
> for LTC parts is different as well as the available HDL for high speed sample
> rate mode. Because of that, I propose creating a new device driver for
> supporting LTC2378-like devices.

Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>

for patches 2-4.

-- 
With Best Regards,
Andy Shevchenko