Add support for AD4000 series of ADCs

Merge series from Marcelo Schmitt <marcelo.schmitt@analog.com>:

This patch series extends the SPI bitbang, gpio, and spi-engine controllers to
support configurable MOSI line idle states.
It then introduces the ad4000 driver which uses the MOSI idle configuration to
provide improved support for the AD4000 series of ADCs.
Documentation is added describing the new extension to the SPI protocol.
The currently supported wiring modes for AD4000 devices were documented under
IIO documentation directory.

Change log v6 -> v7:
[Device tree]
No changes to device tree from v6 to v7.
[SPI]
spi.c: Removed blank line added in code not related to MOSI idle feature.
spi: bitbang: Rewrapped commit message.
spi: bitbang: Rebased bitbang patch on top of spi for-next branch.
[IIO]
ad4000: Checked gain-milli read from dt and made it match one of supported gains or fail.
ad4000: Added blank lines to improve code readability.
ad4000: return 0; when known that no errors occurred.

Link to v6: https://lore.kernel.org/linux-iio/cover.1719686465.git.marcelo.schmitt@analog.com/
Link to v5: https://lore.kernel.org/linux-iio/cover.1719351923.git.marcelo.schmitt@analog.com/
Link to v4: https://lore.kernel.org/linux-iio/cover.1718749981.git.marcelo.schmitt@analog.com/
Link to v3: https://lore.kernel.org/linux-iio/cover.1717539384.git.marcelo.schmitt@analog.com/
Link to v2: https://lore.kernel.org/linux-iio/cover.1712585500.git.marcelo.schmitt@analog.com/
Link to v1: https://lore.kernel.org/linux-iio/cover.1711131830.git.marcelo.schmitt@analog.com/

Prerequisite patches to apply this series to IIO testing branch:

c3358a746e078d0f9048732c90fdab4f37c00e0d "spi: bitbang: Convert unsigned to unsigned int"
https://git.kernel.org/pub/scm/linux/kernel/git/broonie/spi.git/commit/?id=c3358a746e078d0f9048732c90fdab4f37c00e0d

f261172d39f358dcecce13c310690d3937e0cca6 "spi: bitbang: Use typedef for txrx_*() callbacks"
https://git.kernel.org/pub/scm/linux/kernel/git/broonie/spi.git/commit/?id=f261172d39f358dcecce13c310690d3937e0cca6

6ecdb0aa4dca62d236a659426e11e6cf302e8f18 "spi: axi-spi-engine: Add SPI_CS_HIGH support"
https://git.kernel.org/pub/scm/linux/kernel/git/broonie/spi.git/commit/?h=for-6.11&id=6ecdb0aa4dca62d236a659426e11e6cf302e8f18

Prerequisite patches to apply the series to SPI for-next brach:

ef60f9ca26d33d0f8e1a709771c61d3e96f64559 "docs: iio: add documentation for adis16480 driver"
https://git.kernel.org/pub/scm/linux/kernel/git/jic23/iio.git/commit/?h=testing&id=ef60f9ca26d33d0f8e1a709771c61d3e96f64559

Thanks,
Marcelo

Marcelo Schmitt (7):
  spi: Enable controllers to extend the SPI protocol with MOSI idle
    configuration
  spi: bitbang: Implement support for MOSI idle state configuration
  spi: spi-gpio: Add support for MOSI idle state configuration
  spi: spi-axi-spi-engine: Add support for MOSI idle configuration
  dt-bindings: iio: adc: Add AD4000
  iio: adc: Add support for AD4000
  Documentation: Add AD4000 documentation

 .../bindings/iio/adc/adi,ad4000.yaml          | 197 +++++
 Documentation/iio/ad4000.rst                  | 131 ++++
 Documentation/iio/index.rst                   |   1 +
 Documentation/spi/spi-summary.rst             |  83 ++
 MAINTAINERS                                   |   9 +
 drivers/iio/adc/Kconfig                       |  12 +
 drivers/iio/adc/Makefile                      |   1 +
 drivers/iio/adc/ad4000.c                      | 722 ++++++++++++++++++
 drivers/spi/spi-axi-spi-engine.c              |  15 +-
 drivers/spi/spi-bitbang.c                     |  24 +
 drivers/spi/spi-gpio.c                        |  12 +-
 drivers/spi/spi.c                             |   6 +
 include/linux/spi/spi_bitbang.h               |   1 +
 include/uapi/linux/spi/spi.h                  |   5 +-
 14 files changed, 1213 insertions(+), 6 deletions(-)
 create mode 100644 Documentation/devicetree/bindings/iio/adc/adi,ad4000.yaml
 create mode 100644 Documentation/iio/ad4000.rst
 create mode 100644 drivers/iio/adc/ad4000.c

base-commit: 986da024b99a72e64f6bdb3f3f0e52af024b1f50
prerequisite-patch-id: 76a35c35c2af889be2ff20052da02df561b3d71b
prerequisite-patch-id: ce5abb83d4f04e72c69d0df4ded79077065cd649
prerequisite-patch-id: b30f54a92e47dbad33ca7450089c7b19610e9cf2
--
2.43.0

9 files changed, 344 insertions, 6 deletions

diff --git a/Documentation/devicetree/bindings/iio/adc/adi,ad4000.yaml b/Documentation/devicetree/bindings/iio/adc/adi,ad4000.yaml
new file mode 100644
index 000000000000..e413a9d8d2a2
--- /dev/null
+++ b/Documentation/devicetree/bindings/iio/adc/adi,ad4000.yaml
@@ -0,0 +1,197 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/iio/adc/adi,ad4000.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Analog Devices AD4000 and similar Analog to Digital Converters
+
+maintainers:
+  - Marcelo Schmitt <marcelo.schmitt@analog.com>
+
+description: |
+  Analog Devices AD4000 family of Analog to Digital Converters with SPI support.
+  Specifications can be found at:
+    https://www.analog.com/media/en/technical-documentation/data-sheets/ad4000-4004-4008.pdf
+    https://www.analog.com/media/en/technical-documentation/data-sheets/ad4001-4005.pdf
+    https://www.analog.com/media/en/technical-documentation/data-sheets/ad4002-4006-4010.pdf
+    https://www.analog.com/media/en/technical-documentation/data-sheets/ad4003-4007-4011.pdf
+    https://www.analog.com/media/en/technical-documentation/data-sheets/ad4020-4021-4022.pdf
+    https://www.analog.com/media/en/technical-documentation/data-sheets/adaq4001.pdf
+    https://www.analog.com/media/en/technical-documentation/data-sheets/adaq4003.pdf
+
+$ref: /schemas/spi/spi-peripheral-props.yaml#
+
+properties:
+  compatible:
+    oneOf:
+      - const: adi,ad4000
+      - items:
+          - enum:
+              - adi,ad4004
+              - adi,ad4008
+          - const: adi,ad4000
+
+      - const: adi,ad4001
+      - items:
+          - enum:
+              - adi,ad4005
+          - const: adi,ad4001
+
+      - const: adi,ad4002
+      - items:
+          - enum:
+              - adi,ad4006
+              - adi,ad4010
+          - const: adi,ad4002
+
+      - const: adi,ad4003
+      - items:
+          - enum:
+              - adi,ad4007
+              - adi,ad4011
+          - const: adi,ad4003
+
+      - const: adi,ad4020
+      - items:
+          - enum:
+              - adi,ad4021
+              - adi,ad4022
+          - const: adi,ad4020
+
+      - const: adi,adaq4001
+
+      - const: adi,adaq4003
+
+  reg:
+    maxItems: 1
+
+  spi-max-frequency:
+    maximum: 102040816 # for VIO > 2.7 V, 81300813 for VIO > 1.7 V
+
+  adi,sdi-pin:
+    $ref: /schemas/types.yaml#/definitions/string
+    enum: [ high, low, cs, sdi ]
+    default: sdi
+    description:
+      Describes how the ADC SDI pin is wired. A value of "sdi" indicates that
+      the ADC SDI is connected to host SDO. "high" indicates that the ADC SDI
+      pin is hard-wired to logic high (VIO). "low" indicates that it is
+      hard-wired low (GND). "cs" indicates that the ADC SDI pin is connected to
+      the host CS line.
+
+  '#daisy-chained-devices': true
+
+  vdd-supply:
+    description: A 1.8V supply that powers the chip (VDD).
+
+  vio-supply:
+    description:
+      A 1.8V to 5.5V supply for the digital inputs and outputs (VIO).
+
+  ref-supply:
+    description:
+      A 2.5 to 5V supply for the external reference voltage (REF).
+
+  cnv-gpios:
+    description:
+      When provided, this property indicates the GPIO that is connected to the
+      CNV pin.
+    maxItems: 1
+
+  adi,high-z-input:
+    type: boolean
+    description:
+      High-Z mode allows the amplifier and RC filter in front of the ADC to be
+      chosen based on the signal bandwidth of interest, rather than the settling
+      requirements of the switched capacitor SAR ADC inputs.
+
+  adi,gain-milli:
+    description: |
+      The hardware gain applied to the ADC input (in milli units).
+      The gain provided by the ADC input scaler is defined by the hardware
+      connections between chip pins OUT+, R1K-, R1K1-, R1K+, R1K1+, and OUT-.
+      If not present, default to 1000 (no actual gain applied).
+    $ref: /schemas/types.yaml#/definitions/uint16
+    enum: [454, 909, 1000, 1900]
+    default: 1000
+
+  interrupts:
+    description:
+      The SDO pin can also function as a busy indicator. This node should be
+      connected to an interrupt that is triggered when the SDO line goes low
+      while the SDI line is high and the CNV line is low ("3-wire" mode) or the
+      SDI line is low and the CNV line is high ("4-wire" mode); or when the SDO
+      line goes high while the SDI and CNV lines are high (chain mode),
+    maxItems: 1
+
+required:
+  - compatible
+  - reg
+  - vdd-supply
+  - vio-supply
+  - ref-supply
+
+allOf:
+  # The configuration register can only be accessed if SDI is connected to MOSI
+  - if:
+      required:
+        - adi,sdi-pin
+    then:
+      properties:
+        adi,high-z-input: false
+  # chain mode has lower SCLK max rate
+  - if:
+      required:
+        - '#daisy-chained-devices'
+    then:
+      properties:
+        spi-max-frequency:
+          maximum: 50000000 # for VIO > 2.7 V, 40000000 for VIO > 1.7 V
+  # Gain property only applies to ADAQ devices
+  - if:
+      properties:
+        compatible:
+          not:
+            contains:
+              enum:
+                - adi,adaq4001
+                - adi,adaq4003
+    then:
+      properties:
+        adi,gain-milli: false
+
+unevaluatedProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/gpio/gpio.h>
+    spi {
+        #address-cells = <1>;
+        #size-cells = <0>;
+        adc@0 {
+            compatible = "adi,ad4020";
+            reg = <0>;
+            spi-max-frequency = <71000000>;
+            vdd-supply = <&supply_1_8V>;
+            vio-supply = <&supply_1_8V>;
+            ref-supply = <&supply_5V>;
+            adi,sdi-pin = "cs";
+            cnv-gpios = <&gpio0 88 GPIO_ACTIVE_HIGH>;
+        };
+    };
+  - |
+    spi {
+        #address-cells = <1>;
+        #size-cells = <0>;
+        adc@0 {
+            compatible = "adi,adaq4003";
+            reg = <0>;
+            spi-max-frequency = <80000000>;
+            vdd-supply = <&supply_1_8V>;
+            vio-supply = <&supply_1_8V>;
+            ref-supply = <&supply_5V>;
+            adi,high-z-input;
+            adi,gain-milli = /bits/ 16 <454>;
+        };
+    };
diff --git a/Documentation/spi/spi-summary.rst b/Documentation/spi/spi-summary.rst
index 7f8accfae6f9..6e21e6f86912 100644
--- a/Documentation/spi/spi-summary.rst
+++ b/Documentation/spi/spi-summary.rst
@@ -614,6 +614,89 @@ queue, and then start some asynchronous transfer engine (unless it's
 already running).
 
 
+Extensions to the SPI protocol
+------------------------------
+The fact that SPI doesn't have a formal specification or standard permits chip
+manufacturers to implement the SPI protocol in slightly different ways. In most
+cases, SPI protocol implementations from different vendors are compatible among
+each other. For example, in SPI mode 0 (CPOL=0, CPHA=0) the bus lines may behave
+like the following:
+
+::
+
+  nCSx ___                                                                   ___
+          \_________________________________________________________________/
+          •                                                                 •
+          •                                                                 •
+  SCLK         ___     ___     ___     ___     ___     ___     ___     ___
+       _______/   \___/   \___/   \___/   \___/   \___/   \___/   \___/   \_____
+          •   :   ;   :   ;   :   ;   :   ;   :   ;   :   ;   :   ;   :   ; •
+          •   :   ;   :   ;   :   ;   :   ;   :   ;   :   ;   :   ;   :   ; •
+  MOSI XXX__________         _______                 _______         ________XXX
+  0xA5 XXX__/ 1     \_0_____/ 1     \_0_______0_____/ 1     \_0_____/ 1    \_XXX
+          •       ;       ;       ;       ;       ;       ;       ;       ; •
+          •       ;       ;       ;       ;       ;       ;       ;       ; •
+  MISO XXX__________         _______________________          _______        XXX
+  0xBA XXX__/     1 \_____0_/     1       1       1 \_____0__/    1  \____0__XXX
+
+Legend::
+
+  • marks the start/end of transmission;
+  : marks when data is clocked into the peripheral;
+  ; marks when data is clocked into the controller;
+  X marks when line states are not specified.
+
+In some few cases, chips extend the SPI protocol by specifying line behaviors
+that other SPI protocols don't (e.g. data line state for when CS is not
+asserted). Those distinct SPI protocols, modes, and configurations are supported
+by different SPI mode flags.
+
+MOSI idle state configuration
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Common SPI protocol implementations don't specify any state or behavior for the
+MOSI line when the controller is not clocking out data. However, there do exist
+peripherals that require specific MOSI line state when data is not being clocked
+out. For example, if the peripheral expects the MOSI line to be high when the
+controller is not clocking out data (``SPI_MOSI_IDLE_HIGH``), then a transfer in
+SPI mode 0 would look like the following:
+
+::
+
+  nCSx ___                                                                   ___
+          \_________________________________________________________________/
+          •                                                                 •
+          •                                                                 •
+  SCLK         ___     ___     ___     ___     ___     ___     ___     ___
+       _______/   \___/   \___/   \___/   \___/   \___/   \___/   \___/   \_____
+          •   :   ;   :   ;   :   ;   :   ;   :   ;   :   ;   :   ;   :   ; •
+          •   :   ;   :   ;   :   ;   :   ;   :   ;   :   ;   :   ;   :   ; •
+  MOSI _____         _______         _______         _______________         ___
+  0x56      \_0_____/ 1     \_0_____/ 1     \_0_____/ 1       1     \_0_____/
+          •       ;       ;       ;       ;       ;       ;       ;       ; •
+          •       ;       ;       ;       ;       ;       ;       ;       ; •
+  MISO XXX__________         _______________________          _______        XXX
+  0xBA XXX__/     1 \_____0_/     1       1       1 \_____0__/    1  \____0__XXX
+
+Legend::
+
+  • marks the start/end of transmission;
+  : marks when data is clocked into the peripheral;
+  ; marks when data is clocked into the controller;
+  X marks when line states are not specified.
+
+In this extension to the usual SPI protocol, the MOSI line state is specified to
+be kept high when CS is asserted but the controller is not clocking out data to
+the peripheral and also when CS is not asserted.
+
+Peripherals that require this extension must request it by setting the
+``SPI_MOSI_IDLE_HIGH`` bit into the mode attribute of their ``struct
+spi_device`` and call spi_setup(). Controllers that support this extension
+should indicate it by setting ``SPI_MOSI_IDLE_HIGH`` in the mode_bits attribute
+of their ``struct spi_controller``. The configuration to idle MOSI low is
+analogous but uses the ``SPI_MOSI_IDLE_LOW`` mode bit.
+
+
 THANKS TO
 ---------
 Contributors to Linux-SPI discussions include (in alphabetical order,
diff --git a/MAINTAINERS b/MAINTAINERS
index 42decde38320..bc5d242deb29 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -1202,6 +1202,13 @@ W:	https://ez.analog.com/linux-software-drivers
 F:	Documentation/devicetree/bindings/iio/dac/adi,ad3552r.yaml
 F:	drivers/iio/dac/ad3552r.c
 
+ANALOG DEVICES INC AD4000 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,ad4000.yaml
+
 ANALOG DEVICES INC AD4130 DRIVER
 M:	Cosmin Tanislav <cosmin.tanislav@analog.com>
 L:	linux-iio@vger.kernel.org
diff --git a/drivers/spi/spi-axi-spi-engine.c b/drivers/spi/spi-axi-spi-engine.c
index cb3fdcbca2be..2dff95d2b3f5 100644
--- a/drivers/spi/spi-axi-spi-engine.c
+++ b/drivers/spi/spi-axi-spi-engine.c
@@ -41,6 +41,7 @@
 #define SPI_ENGINE_CONFIG_CPHA			BIT(0)
 #define SPI_ENGINE_CONFIG_CPOL			BIT(1)
 #define SPI_ENGINE_CONFIG_3WIRE			BIT(2)
+#define SPI_ENGINE_CONFIG_SDO_IDLE_HIGH		BIT(3)
 
 #define SPI_ENGINE_INST_TRANSFER		0x0
 #define SPI_ENGINE_INST_ASSERT			0x1
@@ -137,6 +138,10 @@ static unsigned int spi_engine_get_config(struct spi_device *spi)
 		config |= SPI_ENGINE_CONFIG_CPHA;
 	if (spi->mode & SPI_3WIRE)
 		config |= SPI_ENGINE_CONFIG_3WIRE;
+	if (spi->mode & SPI_MOSI_IDLE_HIGH)
+		config |= SPI_ENGINE_CONFIG_SDO_IDLE_HIGH;
+	if (spi->mode & SPI_MOSI_IDLE_LOW)
+		config &= ~SPI_ENGINE_CONFIG_SDO_IDLE_HIGH;
 
 	return config;
 }
@@ -692,9 +697,13 @@ static int spi_engine_probe(struct platform_device *pdev)
 	host->num_chipselect = 8;
 
 	/* Some features depend of the IP core version. */
-	if (ADI_AXI_PCORE_VER_MINOR(version) >= 2) {
-		host->mode_bits |= SPI_CS_HIGH;
-		host->setup = spi_engine_setup;
+	if (ADI_AXI_PCORE_VER_MAJOR(version) >= 1) {
+		if (ADI_AXI_PCORE_VER_MINOR(version) >= 2) {
+			host->mode_bits |= SPI_CS_HIGH;
+			host->setup = spi_engine_setup;
+		}
+		if (ADI_AXI_PCORE_VER_MINOR(version) >= 3)
+			host->mode_bits |= SPI_MOSI_IDLE_LOW | SPI_MOSI_IDLE_HIGH;
 	}
 
 	if (host->max_speed_hz == 0)
diff --git a/drivers/spi/spi-bitbang.c b/drivers/spi/spi-bitbang.c
index afb1b1105ec2..ebe18f0b5d23 100644
--- a/drivers/spi/spi-bitbang.c
+++ b/drivers/spi/spi-bitbang.c
@@ -54,21 +54,28 @@ static unsigned int bitbang_txrx_8(struct spi_device *spi,
 	struct spi_transfer	*t,
 	unsigned int flags)
 {
+	struct spi_bitbang	*bitbang;
 	unsigned int		bits = t->bits_per_word;
 	unsigned int		count = t->len;
 	const u8		*tx = t->tx_buf;
 	u8			*rx = t->rx_buf;
 
+	bitbang = spi_controller_get_devdata(spi->controller);
 	while (likely(count > 0)) {
 		u8		word = 0;
 
 		if (tx)
 			word = *tx++;
+		else
+			word = spi->mode & SPI_MOSI_IDLE_HIGH ? 0xFF : 0;
 		word = txrx_word(spi, ns, word, bits, flags);
 		if (rx)
 			*rx++ = word;
 		count -= 1;
 	}
+	if (bitbang->set_mosi_idle)
+		bitbang->set_mosi_idle(spi);
+
 	return t->len - count;
 }
 
@@ -78,21 +85,28 @@ static unsigned int bitbang_txrx_16(struct spi_device *spi,
 	struct spi_transfer	*t,
 	unsigned int flags)
 {
+	struct spi_bitbang	*bitbang;
 	unsigned int		bits = t->bits_per_word;
 	unsigned int		count = t->len;
 	const u16		*tx = t->tx_buf;
 	u16			*rx = t->rx_buf;
 
+	bitbang = spi_controller_get_devdata(spi->controller);
 	while (likely(count > 1)) {
 		u16		word = 0;
 
 		if (tx)
 			word = *tx++;
+		else
+			word = spi->mode & SPI_MOSI_IDLE_HIGH ? 0xFFFF : 0;
 		word = txrx_word(spi, ns, word, bits, flags);
 		if (rx)
 			*rx++ = word;
 		count -= 2;
 	}
+	if (bitbang->set_mosi_idle)
+		bitbang->set_mosi_idle(spi);
+
 	return t->len - count;
 }
 
@@ -102,21 +116,28 @@ static unsigned int bitbang_txrx_32(struct spi_device *spi,
 	struct spi_transfer	*t,
 	unsigned int flags)
 {
+	struct spi_bitbang	*bitbang;
 	unsigned int		bits = t->bits_per_word;
 	unsigned int		count = t->len;
 	const u32		*tx = t->tx_buf;
 	u32			*rx = t->rx_buf;
 
+	bitbang = spi_controller_get_devdata(spi->controller);
 	while (likely(count > 3)) {
 		u32		word = 0;
 
 		if (tx)
 			word = *tx++;
+		else
+			word = spi->mode & SPI_MOSI_IDLE_HIGH ? 0xFFFFFFFF : 0;
 		word = txrx_word(spi, ns, word, bits, flags);
 		if (rx)
 			*rx++ = word;
 		count -= 4;
 	}
+	if (bitbang->set_mosi_idle)
+		bitbang->set_mosi_idle(spi);
+
 	return t->len - count;
 }
 
@@ -192,6 +213,9 @@ int spi_bitbang_setup(struct spi_device *spi)
 			goto err_free;
 	}
 
+	if (bitbang->set_mosi_idle)
+		bitbang->set_mosi_idle(spi);
+
 	dev_dbg(&spi->dev, "%s, %u nsec/bit\n", __func__, 2 * cs->nsecs);
 
 	return 0;
diff --git a/drivers/spi/spi-gpio.c b/drivers/spi/spi-gpio.c
index 36c587be9e28..4f192e013cd6 100644
--- a/drivers/spi/spi-gpio.c
+++ b/drivers/spi/spi-gpio.c
@@ -236,6 +236,14 @@ static void spi_gpio_chipselect(struct spi_device *spi, int is_active)
 	}
 }
 
+static void spi_gpio_set_mosi_idle(struct spi_device *spi)
+{
+	struct spi_gpio *spi_gpio = spi_to_spi_gpio(spi);
+
+	gpiod_set_value_cansleep(spi_gpio->mosi,
+				 !!(spi->mode & SPI_MOSI_IDLE_HIGH));
+}
+
 static int spi_gpio_setup(struct spi_device *spi)
 {
 	struct gpio_desc	*cs;
@@ -389,7 +397,8 @@ static int spi_gpio_probe(struct platform_device *pdev)
 
 	host->bits_per_word_mask = SPI_BPW_RANGE_MASK(1, 32);
 	host->mode_bits = SPI_3WIRE | SPI_3WIRE_HIZ | SPI_CPHA | SPI_CPOL |
-			    SPI_CS_HIGH | SPI_LSB_FIRST;
+			  SPI_CS_HIGH | SPI_LSB_FIRST | SPI_MOSI_IDLE_LOW |
+			  SPI_MOSI_IDLE_HIGH;
 	if (!spi_gpio->mosi) {
 		/* HW configuration without MOSI pin
 		 *
@@ -414,6 +423,7 @@ static int spi_gpio_probe(struct platform_device *pdev)
 	host->flags |= SPI_CONTROLLER_GPIO_SS;
 	bb->chipselect = spi_gpio_chipselect;
 	bb->set_line_direction = spi_gpio_set_direction;
+	bb->set_mosi_idle = spi_gpio_set_mosi_idle;
 
 	if (host->flags & SPI_CONTROLLER_NO_TX) {
 		bb->txrx_word[SPI_MODE_0] = spi_gpio_spec_txrx_word_mode0;
diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 6ebe5dd9bbb1..60a2b5a0c85d 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -3921,6 +3921,12 @@ int spi_setup(struct spi_device *spi)
 		(SPI_TX_DUAL | SPI_TX_QUAD | SPI_TX_OCTAL |
 		 SPI_RX_DUAL | SPI_RX_QUAD | SPI_RX_OCTAL)))
 		return -EINVAL;
+	/* Check against conflicting MOSI idle configuration */
+	if ((spi->mode & SPI_MOSI_IDLE_LOW) && (spi->mode & SPI_MOSI_IDLE_HIGH)) {
+		dev_err(&spi->dev,
+			"setup: MOSI configured to idle low and high at the same time.\n");
+		return -EINVAL;
+	}
 	/*
 	 * Help drivers fail *cleanly* when they need options
 	 * that aren't supported with their current controller.
diff --git a/include/linux/spi/spi_bitbang.h b/include/linux/spi/spi_bitbang.h
index d4cb83195f7a..c92cd43a47f4 100644
--- a/include/linux/spi/spi_bitbang.h
+++ b/include/linux/spi/spi_bitbang.h
@@ -24,6 +24,7 @@ struct spi_bitbang {
 #define	BITBANG_CS_ACTIVE	1	/* normally nCS, active low */
 #define	BITBANG_CS_INACTIVE	0
 
+	void	(*set_mosi_idle)(struct spi_device *spi);
 	/* txrx_bufs() may handle dma mapping for transfers that don't
 	 * already have one (transfer.{tx,rx}_dma is zero), or use PIO
 	 */
diff --git a/include/uapi/linux/spi/spi.h b/include/uapi/linux/spi/spi.h
index ca56e477d161..ee4ac812b8f8 100644
--- a/include/uapi/linux/spi/spi.h
+++ b/include/uapi/linux/spi/spi.h
@@ -28,7 +28,8 @@
 #define	SPI_RX_OCTAL		_BITUL(14)	/* receive with 8 wires */
 #define	SPI_3WIRE_HIZ		_BITUL(15)	/* high impedance turnaround */
 #define	SPI_RX_CPHA_FLIP	_BITUL(16)	/* flip CPHA on Rx only xfer */
-#define SPI_MOSI_IDLE_LOW	_BITUL(17)	/* leave mosi line low when idle */
+#define SPI_MOSI_IDLE_LOW	_BITUL(17)	/* leave MOSI line low when idle */
+#define SPI_MOSI_IDLE_HIGH	_BITUL(18)	/* leave MOSI line high when idle */
 
 /*
  * All the bits defined above should be covered by SPI_MODE_USER_MASK.
@@ -38,6 +39,6 @@
  * These bits must not overlap. A static assert check should make sure of that.
  * If adding extra bits, make sure to increase the bit index below as well.
  */
-#define SPI_MODE_USER_MASK	(_BITUL(18) - 1)
+#define SPI_MODE_USER_MASK	(_BITUL(19) - 1)
 
 #endif /* _UAPI_SPI_H */