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docs: iio: Add documentation for MAX22007 driver
Add documentation for MAX22007 driver which describes how the user can access the driver using dtoverlays Signed-off-by: Janani Sunil <[email protected]>
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‎Documentation/iio/index.rst‎

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adxl380
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bno055
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ep93xx_adc
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max22007

‎Documentation/iio/max22007.rst‎

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.. SPDX-License-Identifier: GPL-2.0-only
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===============
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MAX22007 driver
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===============
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Device driver for Analog Devices Inc. MAX22007 quad-channel industrial DAC.
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The module name is ``max22007``.
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The MAX22007 is a quad-channel, 12-bit digital-to-analog converter (DAC) with
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integrated precision output amplifiers and current output capability. Each
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channel can be independently configured for voltage or current output mode.
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Supported devices
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=================
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* `MAX22007 <https://www.analog.com/en/products/max22007.html>`_
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Device Features
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===============
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* 4 independent DAC channels
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* 12-bit resolution
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* Configurable voltage or current output per channel
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* Configurable latch modes (LDAC control or transparent)
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* Individual channel power control
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* SPI interface with CRC8 error checking
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* Industrial temperature range operation
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Wiring connections
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==================
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The MAX22007 uses a standard SPI interface:
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::
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.----------------. .----------.
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| |--- SPI_CLK ----| |
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| SPI Master |--- SPI_CS -----| MAX22007 |
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| |--- SPI_MOSI ---| |
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| |--- SPI_MISO ---| |
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|________________| |__________|
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Device Tree Configuration
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=========================
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The device supports per-channel configuration through device tree. Each channel
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can be configured with the following optional properties:
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* ``adi,dac-latch-mode``: Controls when DAC updates occur
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- 0: LDAC pin controls the latch (default)
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- 1: Transparent latch mode (immediate update)
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* ``adi,channel-mode``: Sets the output mode
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- 0: Voltage output mode (default)
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- 1: Current output mode
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* ``adi,channel-power``: Controls channel power state
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- 0: Channel powered off
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- 1: Channel powered on (default)
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Example device tree configuration:
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.. code-block:: devicetree
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dac@0 {
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compatible = "adi,max22007";
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reg = <0>;
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spi-max-frequency = <25000000>;
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#address-cells = <1>;
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#size-cells = <0>;
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channel@0 {
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reg = <0>;
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adi,channel-mode = <0>; /* Voltage output */
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adi,dac-latch-mode = <0>; /* LDAC control */
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adi,channel-power = <1>; /* Powered on */
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};
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channel@1 {
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reg = <1>;
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adi,channel-mode = <1>; /* Current output */
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};
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};
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Sysfs Interface
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===============
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The MAX22007 driver provides standard IIO DAC interfaces. Each channel appears
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as a separate IIO device attribute:
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* ``out_voltage_raw`` (voltage mode channels)
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* ``out_current_raw`` (current mode channels)
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The driver automatically configures the IIO channel type based on the configured
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channel mode from device tree.
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Usage Examples
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==============
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Setting DAC output value:
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.. code-block:: bash
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# Set channel 0 (voltage mode) to mid-scale
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echo 2048 > /sys/bus/iio/devices/iio:deviceX/out_voltage0_raw
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# Set channel 1 (current mode) to quarter scale
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echo 1024 > /sys/bus/iio/devices/iio:deviceX/out_current1_raw
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Reading current DAC value:
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.. code-block:: bash
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# Read channel 0 value
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cat /sys/bus/iio/devices/iio:deviceX/out_voltage0_raw
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Channel Information:
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.. code-block:: bash
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# Check available channels
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ls /sys/bus/iio/devices/iio:deviceX/out_*_raw
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Register Access
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===============
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The MAX22007 device provides register access through debugfs when the driver
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is compiled with debug support. This allows direct hardware register access
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for debugging and advanced configuration.
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Register Map
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------------
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The MAX22007 uses the following register mapping:
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.. list-table::
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:header-rows: 1
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* - Address
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- Register Name
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- Description
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* - 0x03
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- CONFIG_REG
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- Configuration register (CRC enable, DAC latch modes)
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* - 0x05
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- CHANNEL_MODE_REG
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- Channel mode and power control
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* - 0x06
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- SOFT_RESET_REG
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- Software reset control
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* - 0x07-0x0A
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- DAC_CHANNEL_REG(0-3)
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- DAC data registers for channels 0-3
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Register Access via Debugfs
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----------------------------
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When debugfs is enabled, the driver exposes register access through:
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.. code-block:: bash
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# Navigate to the device debugfs directory
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cd /sys/kernel/debug/iio/iio:deviceX/
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# Read a register (example: read CONFIG_REG at address 0x03)
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echo 0x03 > direct_reg_access
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cat direct_reg_access
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# Write to a register (example: write 0x1234 to CONFIG_REG)
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echo 0x03 0x1234 > direct_reg_access
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Programming Examples
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--------------------
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**Direct Register Programming**:
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.. code-block:: bash
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# Enable CRC (set bit 0 in CONFIG_REG)
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echo 0x03 0x0001 > /sys/kernel/debug/iio/iio:deviceX/direct_reg_access
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# Set channel 0 to voltage mode and power on (clear bit 12, set bit 8 in CHANNEL_MODE_REG)
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echo 0x05 0x0100 > /sys/kernel/debug/iio/iio:deviceX/direct_reg_access
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# Set DAC channel 0 to mid-scale (0x800 shifted to bits [15:4])
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echo 0x07 0x8000 > /sys/kernel/debug/iio/iio:deviceX/direct_reg_access
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**Reading Register Values**:
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.. code-block:: bash
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# Read current channel mode configuration
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echo 0x05 > /sys/kernel/debug/iio/iio:deviceX/direct_reg_access
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cat /sys/kernel/debug/iio/iio:deviceX/direct_reg_access
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# Read DAC channel 0 current value
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echo 0x07 > /sys/kernel/debug/iio/iio:deviceX/direct_reg_access
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cat /sys/kernel/debug/iio/iio:deviceX/direct_reg_access
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Driver Architecture
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===================
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The driver implements the following key features:
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* **CRC8 Error Checking**: All SPI communications use CRC8 for data integrity
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* **Channel Configuration**: Supports per-channel mode and power configuration
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* **Register Map**: Uses regmap for efficient register access and caching
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* **IIO Integration**: Full integration with the Linux IIO subsystem
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* **Debugfs Access**: Direct register access for debugging and development
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Notes and Limitations
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=====================
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* Channel configuration (voltage/current mode) is set at device tree parsing
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and cannot be changed dynamically
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* The driver requires proper device tree configuration for optimal operation
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* CRC error detection helps ensure data integrity in noisy industrial environments

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