[PATCH v4 0/4] iio: adc: Add support for LTC2378 and similar ADCs

[PATCH v4 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

Despite the initial version of the LTC2378 driver had been developed by
Ioan-Daniel. The current version has been greatly rewritten such that very
little remained from that initial version. Due to that, having Ioan-Daniel in
the author list now seems inaccurate.

Previous submissions:
  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 v3 -> v4:
[DT]
- Added PWM property.
- Documented LTC2338-18 specific refin-supply.
- Picked up Conor's review tag.
[IIO]
- Dropped DMAengine buffer changes.
- Reworked the driver to make IIO channels static according to v3 feedback.
- Updated to use default 8 bits_per_word for non-offloaded transfers.
- Handled refin voltage reference supply for LTC2338.
- Used spi_bpw_to_bytes() where applicable.

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         | 185 +++++
 MAINTAINERS                                   |   8 +
 drivers/iio/adc/Kconfig                       |  19 +
 drivers/iio/adc/Makefile                      |   1 +
 drivers/iio/adc/ltc2378.c                     | 778 ++++++++++++++++++
 5 files changed, 991 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/iio/adc/adi,ltc2378.yaml
 create mode 100644 drivers/iio/adc/ltc2378.c


base-commit: cc746297b23e89bd5df9f91f3a0ca209e8991763
-- 
2.53.0

[PATCH v4 1/4] dt-bindings: iio: adc: Add ltc2378

[Marcelo Schmitt]

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

Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Marcelo Schmitt <marcelo.schmitt@analog.com>
---
Change log v3 -> v4:
- Added PWM property.
- Documented LTC2338-18 specific refin-supply.
- Picked up Conor's review tag.

 .../bindings/iio/adc/adi,ltc2378.yaml         | 185 ++++++++++++++++++
 MAINTAINERS                                   |   7 +
 2 files changed, 192 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..9adc420fe142
--- /dev/null
+++ b/Documentation/devicetree/bindings/iio/adc/adi,ltc2378.yaml
@@ -0,0 +1,185 @@
+# 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,ltc2367-16
+          - adi,ltc2367-18
+          - adi,ltc2368-16
+          - adi,ltc2368-18
+          - adi,ltc2369-18
+          - adi,ltc2370-16
+          - adi,ltc2376-16
+          - adi,ltc2376-18
+          - adi,ltc2376-20
+          - adi,ltc2377-16
+          - adi,ltc2377-18
+          - adi,ltc2377-20
+          - adi,ltc2378-16
+          - adi,ltc2378-18
+          - adi,ltc2378-20
+          - adi,ltc2379-18
+          - adi,ltc2380-16
+
+      # 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,ltc2338-18 # 1 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 b051eccafa60..205acb4b0789 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -15220,6 +15220,13 @@ 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 v4 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.

Signed-off-by: Marcelo Schmitt <marcelo.schmitt@analog.com>
---
Change log v3 -> v4:
- Reworked the driver to make IIO channels static according to v3 feedback.
- Updated to use default 8 bits_per_word for non-offloaded transfers.
- Handled refin voltage reference supply for LTC2338.
- Used spi_bpw_to_bytes() where applicable.

 MAINTAINERS               |   1 +
 drivers/iio/adc/Kconfig   |  12 ++
 drivers/iio/adc/Makefile  |   1 +
 drivers/iio/adc/ltc2378.c | 395 ++++++++++++++++++++++++++++++++++++++
 4 files changed, 409 insertions(+)
 create mode 100644 drivers/iio/adc/ltc2378.c

diff --git a/MAINTAINERS b/MAINTAINERS
index 205acb4b0789..db24dfa087d9 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -15226,6 +15226,7 @@ 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 756a3b1137a7..07a8a5911a09 100644
--- a/drivers/iio/adc/Kconfig
+++ b/drivers/iio/adc/Kconfig
@@ -941,6 +941,18 @@ 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 707dd708912f..1814fb78dde3 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..9a9f32e4989b
--- /dev/null
+++ b/drivers/iio/adc/ltc2378.c
@@ -0,0 +1,395 @@
+// 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/cleanup.h>
+#include <linux/delay.h>
+#include <linux/err.h>
+#include <linux/gpio/consumer.h>
+#include <linux/mod_devicetable.h>
+#include <linux/module.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_DIFF_CHANNEL(_sign, _real_bits, _storage_bits, _offl)\
+{										\
+	.type = IIO_VOLTAGE,							\
+	.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |				\
+			      BIT(IIO_CHAN_INFO_SCALE) |			\
+			      (_offl ? BIT(IIO_CHAN_INFO_SAMP_FREQ) : 0),	\
+	.info_mask_separate_available = _offl ? BIT(IIO_CHAN_INFO_SAMP_FREQ) : 0,\
+	.scan_index = 0,							\
+	.scan_type = {								\
+		.format = _sign ? IIO_SCAN_FORMAT_SIGNED_INT :			\
+				  IIO_SCAN_FORMAT_UNSIGNED_INT,			\
+		.realbits = _real_bits,						\
+		.storagebits = _storage_bits,					\
+		.shift = (_offl ? 0 : _storage_bits - _real_bits),		\
+		.endianness = _offl ? IIO_CPU : IIO_BE				\
+	},									\
+}
+
+#define LTC2378_BIPOLAR_DIFF_CHANNEL(_real_bits)				\
+	__LTC2378_DIFF_CHANNEL(1, _real_bits, (((_real_bits) > 16) ? 32 : 16), 0)
+
+#define LTC2378_UNIPOLAR_DIFF_CHANNEL(_real_bits)				\
+	__LTC2378_DIFF_CHANNEL(0, _real_bits, (((_real_bits) > 16) ? 32 : 16), 0)
+
+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 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);
+};
+
+static const struct ltc2378_chip_info ltc2338_18_chip_info = {
+	.name = "ltc2338-18",
+	.internal_ref_uv = 4096000,
+	.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(4);
+	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;
+
+	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 {
+		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_regulator_setup(struct device *dev, struct ltc2378_state *st)
+{
+	int ret;
+
+	ret = devm_regulator_get_enable_read_voltage(dev, "refin");
+	if (ret < 0 && ret != -ENODEV) {
+		return dev_err_probe(dev, ret, "failed to read refin regulator\n");
+	} else if (ret > 0) {
+		st->ref_uV = ret;
+		return 0;
+	}
+
+	if (st->info->internal_ref_uv) {
+		st->ref_uV = st->info->internal_ref_uv;
+		return 0;
+	}
+
+	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;
+
+	st->info = spi_get_device_match_data(spi);
+	if (!st->info)
+		return -EINVAL;
+
+	ret = ltc2378_regulator_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 v4 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).

Signed-off-by: Marcelo Schmitt <marcelo.schmitt@analog.com>
---
Change log v3 -> v4:
- Squashed offload support into main driver since selecting SPI_OFFLOAD and
  depending on PWM is acceptable.

 drivers/iio/adc/Kconfig   |   6 +
 drivers/iio/adc/ltc2378.c | 359 +++++++++++++++++++++++++++++++++++++-
 2 files changed, 362 insertions(+), 3 deletions(-)

diff --git a/drivers/iio/adc/Kconfig b/drivers/iio/adc/Kconfig
index 07a8a5911a09..8d2fadbf74b1 100644
--- a/drivers/iio/adc/Kconfig
+++ b/drivers/iio/adc/Kconfig
@@ -946,6 +946,12 @@ 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 9a9f32e4989b..5b28630003b1 100644
--- a/drivers/iio/adc/ltc2378.c
+++ b/drivers/iio/adc/ltc2378.c
@@ -12,16 +12,29 @@
 #include <linux/delay.h>
 #include <linux/err.h>
 #include <linux/gpio/consumer.h>
+#include <linux/math.h>
+#include <linux/math64.h>
 #include <linux/mod_devicetable.h>
 #include <linux/module.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/sysfs.h>
 #include <linux/iio/types.h>
 
+#define LTC2378_TDSDOBUSYL_NS		5
+#define LTC2378_TBUSYLH_NS		13
+#define LTC2378_TCNV_HIGH_NS		20
+
 #define __LTC2378_DIFF_CHANNEL(_sign, _real_bits, _storage_bits, _offl)\
 {										\
 	.type = IIO_VOLTAGE,							\
@@ -46,10 +59,19 @@
 #define LTC2378_UNIPOLAR_DIFF_CHANNEL(_real_bits)				\
 	__LTC2378_DIFF_CHANNEL(0, _real_bits, (((_real_bits) > 16) ? 32 : 16), 0)
 
+#define LTC2378_OFFLOAD_BIPOLAR_DIFF_CHANNEL(_real_bits)			\
+	__LTC2378_DIFF_CHANNEL(1, (_real_bits), 32, 1)
+
+#define LTC2378_OFFLOAD_UNIPOLAR_DIFF_CHANNEL(_real_bits)			\
+	__LTC2378_DIFF_CHANNEL(0, (_real_bits), 32, 1)
+
 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 {
@@ -58,6 +80,15 @@ struct ltc2378_state {
 	struct spi_device *spi;
 	struct spi_transfer xfer;
 	int ref_uV;
+	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;
+	unsigned int sample_freq_range[3];
 
 	/*
 	 * DMA (thus cache coherency maintenance) requires the
@@ -78,101 +109,161 @@ static const struct ltc2378_chip_info ltc2338_18_chip_info = {
 	.name = "ltc2338-18",
 	.internal_ref_uv = 4096000,
 	.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)
@@ -254,7 +345,126 @@ 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 = 0;
+	u64 offload_offset_ns;
+	int ret;
+
+	if (freq_Hz == 0)
+		return -EINVAL;
+
+	if (freq_Hz < 1 || freq_Hz > 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.
+	 */
+	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++ < 100 && cnv_wf.duty_length_ns < LTC2378_TCNV_HIGH_NS);
+
+	/* Double check the minimum CNV high time is met */
+	if (cnv_wf.duty_length_ns < LTC2378_TCNV_HIGH_NS)
+		return -EIO;
+
+	/*
+	 * 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;
+	count = 0;
+	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++ < 100 && 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);
+
+	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;
 	}
@@ -264,6 +474,111 @@ 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_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_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, false);
+	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_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_regulator_setup(struct device *dev, struct ltc2378_state *st)
 {
 	int ret;
@@ -313,7 +628,6 @@ 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);
@@ -321,8 +635,46 @@ 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");
+	}
 
 	st->xfer.rx_buf = &st->scan.data;
 	st->xfer.len = spi_bpw_to_bytes(indio_dev->channels[0].scan_type.realbits);
@@ -393,3 +745,4 @@ 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");
-- 
2.53.0

[PATCH v4 4/4] iio: adc: ltc2378: Enable triggered buffer data capture

[Marcelo Schmitt]

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

Signed-off-by: Marcelo Schmitt <marcelo.schmitt@analog.com>
---
Change log v3 -> v4:
- Squashed triggered buffer support into main driver.

 drivers/iio/adc/Kconfig   |  1 +
 drivers/iio/adc/ltc2378.c | 76 +++++++++++++++++++++++++++------------
 2 files changed, 54 insertions(+), 23 deletions(-)

diff --git a/drivers/iio/adc/Kconfig b/drivers/iio/adc/Kconfig
index 8d2fadbf74b1..ac162425dc91 100644
--- a/drivers/iio/adc/Kconfig
+++ b/drivers/iio/adc/Kconfig
@@ -950,6 +950,7 @@ 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 5b28630003b1..fcccd2774549 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/cleanup.h>
@@ -29,6 +30,8 @@
 #include <linux/iio/buffer-dmaengine.h>
 #include <linux/iio/iio.h>
 #include <linux/iio/sysfs.h>
+#include <linux/iio/triggered_buffer.h>
+#include <linux/iio/trigger_consumer.h>
 #include <linux/iio/types.h>
 
 #define LTC2378_TDSDOBUSYL_NS		5
@@ -68,7 +71,7 @@
 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;
@@ -108,7 +111,7 @@ struct ltc2378_state {
 static const struct ltc2378_chip_info ltc2338_18_chip_info = {
 	.name = "ltc2338-18",
 	.internal_ref_uv = 4096000,
-	.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,
@@ -116,7 +119,7 @@ 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,
@@ -124,7 +127,7 @@ 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,
@@ -132,7 +135,7 @@ 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,
@@ -140,7 +143,7 @@ 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,
@@ -148,7 +151,7 @@ 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,
@@ -156,7 +159,7 @@ 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,
@@ -164,7 +167,7 @@ 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,
@@ -172,7 +175,7 @@ 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,
@@ -180,7 +183,7 @@ 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,
@@ -188,7 +191,7 @@ 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,
@@ -196,7 +199,7 @@ 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,
@@ -204,7 +207,7 @@ 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,
@@ -212,7 +215,7 @@ 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,
@@ -220,7 +223,7 @@ 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,
@@ -228,7 +231,7 @@ 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,
@@ -236,7 +239,7 @@ 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,
@@ -244,7 +247,7 @@ 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,
@@ -252,7 +255,7 @@ 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,
@@ -260,7 +263,7 @@ 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,
@@ -279,6 +282,25 @@ 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)
 {
@@ -640,8 +662,16 @@ 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 dev_err_probe(dev, ret,
+					     "failed to setup triggered buffer\n");
 	} else if (ret) {
 		return dev_err_probe(dev, ret, "failed to get offload\n");
 	} else {
-- 
2.53.0

Re: [PATCH v4 1/4] dt-bindings: iio: adc: Add ltc2378

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] The compatible string 'adi,ltc2338-18' incorrectly specifies 'adi,ltc2376-18' as a fallback despite conflicting hardware constraints for 'ref-supply', breaking backward compatibility.
--

commit aa175408226610e4bc2c27ed8ee768b0307ee6fa
Author: Marcelo Schmitt <marcelo.schmitt@analog.com>

dt-bindings: iio: adc: Add ltc2378

This commit documents the device tree bindings for the Analog Devices LTC2378
and similar series of ADCs. It specifies the compatible strings, required
properties, and voltage reference constraints.

> 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 0000000000000..9adc420fe142b
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/iio/adc/adi,ltc2378.yaml
[ ... ]
> +      # Low sample rate fallback for 18-bit bipolar sensors.
> +      - items:
> +          - enum:
> +              - adi,ltc2379-18 # 1.6 MSPS
> +              - adi,ltc2338-18 # 1 MSPS
> +              - adi,ltc2378-18 # 1 MSPS
> +              - adi,ltc2377-18 # 500 kSPS
> +          - const: adi,ltc2376-18 # fallback (250 kSPS)
[ ... ]
> +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

[Severity: Medium]
Will this cause probe failures on older kernels when using the fallback?

The compatible string adi,ltc2338-18 is configured to use adi,ltc2376-18 as a
fallback. However, this conditional block strictly forbids the ref-supply
property for adi,ltc2338-18.

Because adi,ltc2376-18 requires a ref-supply, a device tree correctly following
this binding for adi,ltc2338-18 will lack that property.

When an older kernel attempts to bind using the adi,ltc2376-18 fallback string,
will it fail to find the expected ref-supply regulator and abort probing?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/cover.1782397418.git.marcelo.schmitt@analog.com?part=1

Re: [PATCH v4 2/4] iio: adc: ltc2378: Add support for LTC2378-20 and similar ADCs

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
- [High] The voltage from the 'refin' regulator is not multiplied by the internal buffer gain, resulting in incorrect ADC scale.
- [Medium] External 'ref' regulator is completely ignored for chips with an internal reference, breaking the ability to overdrive the internal reference.
--

commit 06f09452b5298cd69acd94f1c33c2c91342a505d
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..9a9f32e4989ba
> --- /dev/null
> +++ b/drivers/iio/adc/ltc2378.c
[ ... ]
> +static int ltc2378_regulator_setup(struct device *dev, struct ltc2378_state *st)
> +{
> +	int ret;
> +
> +	ret = devm_regulator_get_enable_read_voltage(dev, "refin");
> +	if (ret < 0 && ret != -ENODEV) {
> +		return dev_err_probe(dev, ret, "failed to read refin regulator\n");
> +	} else if (ret > 0) {
> +		st->ref_uV = ret;

[Severity: High]
Does this assignment account for the internal buffer's amplification gain?

For example, on chips like the LTC2338-18, the internal reference buffer
amplifies the REFIN voltage by a factor of 2. If the 'refin' regulator provides
2.048V, the internal REF pin sees 4.096V. But this code appears to assign the
direct REFIN voltage to st->ref_uV, which would result in an incorrect ADC
scale calculation.

> +		return 0;
> +	}
> +
> +	if (st->info->internal_ref_uv) {
> +		st->ref_uV = st->info->internal_ref_uv;
> +		return 0;

[Severity: Medium]
Does this early return prevent a board from overdriving the internal reference
with an external 'ref' supply?

If the hardware supports overdriving the internal reference and a 'ref-supply'
is provided in the device tree, it looks like this code will silently ignore
it and use the internal reference value instead.

> +	}
> +
> +	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;
> +}
[ ... ]

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/cover.1782397418.git.marcelo.schmitt@analog.com?part=2

Re: [PATCH v4 3/4] iio: adc: ltc2378: Enable high-speed data capture

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 4 potential issue(s) to consider:
- [High] Missing verification of SPI offload trigger offset after validation loop in `ltc2378_update_conversion_rate()` allows silent data corruption.
- [Medium] In-out parameters accumulate drift across iterative rounding loops in `ltc2378_update_conversion_rate()`.
- [Medium] Torn state on error path in `ltc2378_update_conversion_rate()` due to partially updated `st->offload_trigger_config`.
- [Low] Data race on `st->cnv_Hz` between sysfs readers and writers.
--

commit 57c4b9b3af36aafb3888623014ea397ad6cf0cd6
Author: Marcelo Schmitt <marcelo.schmitt@analog.com>

iio: adc: ltc2378: Enable high-speed data capture
    
Make use of SPI transfer offloading to speed up data capture, enabling data
acquisition at faster sample rates (up to 2 MSPS).

> diff --git a/drivers/iio/adc/ltc2378.c b/drivers/iio/adc/ltc2378.c
> --- a/drivers/iio/adc/ltc2378.c
> +++ b/drivers/iio/adc/ltc2378.c
[ ... ]
> @@ -254,7 +345,126 @@ 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;

[Severity: Low]
When reading the frequency via ltc2378_read_raw(), st->cnv_Hz is read without
acquiring the direct mode lock. Since it can be concurrently modified by
ltc2378_update_conversion_rate() during a write, does this cause a data race?
Should this be protected or accessed via READ_ONCE()?

> +		return IIO_VAL_INT;
> +	default:
> +		return -EINVAL;
> +	}
> +}
[ ... ]
> +static int ltc2378_update_conversion_rate(struct ltc2378_state *st, int freq_Hz)
> +{
[ ... ]
> +	/* 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.
> +	 */
> +	do {
> +		cnv_wf.duty_length_ns = target;
> +		ret = pwm_round_waveform_might_sleep(st->cnv_trigger, &cnv_wf);

[Severity: Medium]
The pwm_round_waveform_might_sleep() function can modify the passed cnv_wf
structure in place. Since the base period (cnv_wf.period_length_ns) is set
before the loop and not reset inside, does this cause the period to drift
across the iterations if the hardware constraints cause it to be repeatedly
rounded?

> +		if (ret)
> +			return ret;
> +		target += 10;  /* Increment by PWM duty cycle period */
> +	} while (count++ < 100 && cnv_wf.duty_length_ns < LTC2378_TCNV_HIGH_NS);
> +
> +	/* Double check the minimum CNV high time is met */
> +	if (cnv_wf.duty_length_ns < LTC2378_TCNV_HIGH_NS)
> +		return -EIO;
> +
> +	/*
> +	 * 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;
> +	count = 0;
> +	do {
> +		config->periodic.offset_ns = offload_offset_ns;
> +		ret = spi_offload_trigger_validate(st->offload_trigger, config);

[Severity: Medium]
The config pointer aliases st->offload_trigger_config. If this validation
fails, the function returns the error directly below without rolling back
the st->offload_trigger_config state. Could this leave the device in an
inconsistent state where the old st->cnv_wf configuration is paired with
a newly modified but rejected SPI trigger configuration upon the next
postenable?

Additionally, similar to the PWM loop above, spi_offload_trigger_validate()
modifies config in place. Does config->periodic.frequency_hz drift across
iterations since it is not reset inside the loop?

> +		if (ret)
> +			return ret;
> +		offload_offset_ns += 10;
> +	} while (count++ < 100 && config->periodic.offset_ns < min_read_offset);

[Severity: High]
If the loop exhausts its 100 retries without meeting the minimum offset
requirement, won't it silently proceed here without returning an error?

Unlike the preceding PWM loop which explicitly checks the bounds afterward,
could this missing check cause silent data corruption if the SPI controller
ends up reading while the ADC is still converting?

> +
> +	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.1782397418.git.marcelo.schmitt@analog.com?part=3

Re: [PATCH v4 4/4] iio: adc: ltc2378: Enable triggered buffer data capture

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:

Pre-existing issues:
- [High] Single reads via sysfs (`in_voltage0_raw`) return scrambled/garbage data when the SPI offload engine is configured, because they incorrectly use the offload channel's endianness and shift properties.
--

commit 5a2926870e368170637e86d31e6346617e37a6b1
Author: Marcelo Schmitt <marcelo.schmitt@analog.com>

iio: adc: ltc2378: Enable triggered buffer data capture
    
Enable users to run triggered data captures with LTC2378 and similar ADCs.

> diff --git a/drivers/iio/adc/ltc2378.c b/drivers/iio/adc/ltc2378.c
> index 5b28630003b18..fcccd27745490 100644
> --- a/drivers/iio/adc/ltc2378.c
> +++ b/drivers/iio/adc/ltc2378.c

[ ... ]

> @@ -640,8 +662,16 @@ 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 dev_err_probe(dev, ret,
> +					     "failed to setup triggered buffer\n");
>  	} else if (ret) {
>  		return dev_err_probe(dev, ret, "failed to get offload\n");
>  	} else {

[Severity: High]
This is a pre-existing issue, but do single reads via sysfs
(in_voltage0_raw) return scrambled data when the SPI offload engine is
configured?

When offload is configured, indio_dev->channels is assigned to the
offload channel just after this else block in ltc2378_probe():

		indio_dev->channels = &st->info->offload_chan;

This channel specification is later passed to ltc2378_channel_single_read().
However, the single read function relies on the channel's endianness and
shift properties to decode the raw SPI data:

static int ltc2378_channel_single_read(const struct iio_chan_spec *chan, ...)
{
	...
	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 {
		if (chan->scan_type.realbits > 16)
			sample = st->scan.data.sample_buf32;
		else
			sample = st->scan.data.sample_buf16;
	}

	sample >>= chan->scan_type.shift;
	...
}

Because the offload_chan specification defines data as CPU-endian with
a 0 shift, the else branch is taken. This treats the natively big-endian,
MSB-aligned SPI data as unshifted CPU-endian data, scrambling the values on
little-endian architectures.

Could this be updated to properly handle manual sysfs reads when offload
is enabled?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/cover.1782397418.git.marcelo.schmitt@analog.com?part=4