[PATCH v6 16/16] docs: iio: add documentation for ad9910 driver

[Rodrigo Alencar via B4 Relay]

From: Rodrigo Alencar <rodrigo.alencar@xxxxxxxxxx>

Add documentation for the AD9910 DDS IIO driver, which describes channels,
DDS modes, attributes and ABI usage examples.

Signed-off-by: Rodrigo Alencar <rodrigo.alencar@xxxxxxxxxx>
---
 Documentation/iio/ad9910.rst | 759 +++++++++++++++++++++++++++++++++++++++++++
 Documentation/iio/index.rst  |   1 +
 MAINTAINERS                  |   1 +
 3 files changed, 761 insertions(+)

diff --git a/Documentation/iio/ad9910.rst b/Documentation/iio/ad9910.rst
new file mode 100644
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@@ -0,0 +1,759 @@
+.. SPDX-License-Identifier: GPL-2.0-only
+
+=============
+AD9910 driver
+=============
+
+Direct Digital Synthesizer (DDS) driver for the Analog Devices Inc. AD9910.
+The module name is ``ad9910``.
+
+* `AD9910 <https://www.analog.com/en/products/ad9910.html>`_
+
+The AD9910 is a 1 GSPS DDS with a 14-bit DAC, controlled over SPI. The driver
+exposes the device through a hierarchy of typed IIO output channels. The root
+``phy`` channel controls the system clock and full-scale output current.
+Sub-channels provide independent control over single tone profiles, parallel
+port modulation, digital ramp generation (DRG), RAM playback and output shift
+keying (OSK).
+
+
+Channel hierarchy
+=================
+
+The driver exposes the following IIO output channels, each identified by a
+unique channel number and a human-readable label. The ``phy`` channel is the
+root of the hierarchy. Changing its ``sampling_frequency`` reconfigures the
+system clock (SYSCLK) which affects all other channels.
+
+.. flat-table::
+   :header-rows: 1
+
+   * - Channel
+     - Label
+     - Parent
+     - Description
+
+   * - ``out_altcurrent100``
+     - ``phy``
+     -
+     - Physical output: system clock and full-scale output current (:math:`I_{FS}`).
+       See `Physical channel`_.
+
+   * - ``out_altcurrent110`` ... ``out_altcurrent117``
+     - ``profile0`` ... ``profile7``
+     - ``phy``
+     - Single tone control: frequency, phase, amplitude, enable.
+       See `Single Tone mode`_.
+
+   * - ``out_altcurrent120``
+     - ``parallel_amplitude``
+     - ``phy``
+     - Parallel port amplitude channel.
+       See `Parallel Port mode`_.
+
+   * - ``out_phase120``
+     - ``parallel_phase``
+     - ``phy``
+     - Parallel port phase channel.
+
+   * - ``out_frequency120``
+     - ``parallel_frequency``
+     - ``phy``
+     - Parallel port frequency channel: ``scale`` sets the FM gain
+       (power-of-2 multiplier), ``offset`` sets the base FTW.
+
+   * - ``out_altcurrent121``
+     - ``parallel_polar_amplitude``
+     - ``phy``
+     - Parallel polar amplitude channel: ``scale`` is the amplitude
+       resolution, ``offset`` is the amplitude bias (lower 6 bits of ASF).
+
+   * - ``out_phase121``
+     - ``parallel_polar_phase``
+     - ``phy``
+     - Parallel polar phase channel: ``scale`` is the phase resolution,
+       ``offset`` is the phase bias (lower 8 bits of POW).
+
+   * - ``out_frequency130``
+     - ``drg_frequency``
+     - ``phy``
+     - DRG frequency channel: ``en`` selects and enables the DRG with
+       frequency as the ramp target.
+
+   * - ``out_phase130``
+     - ``drg_phase``
+     - ``phy``
+     - DRG phase channel: ``en`` selects and enables the DRG with phase
+       as the ramp target.
+
+   * - ``out_altcurrent130``
+     - ``drg_amplitude``
+     - ``phy``
+     - DRG amplitude channel: ``en`` selects and enables the DRG with
+       amplitude as the ramp target.
+       See `Digital ramp generator (DRG)`_.
+
+   * - ``out_altcurrent131``
+     - ``drg_rising``
+     - ``drg_amplitude``
+     - DRG rising-ramp parameters: limit code, dwell enable, ramp clock,
+       rate of change.
+
+   * - ``out_altcurrent132``
+     - ``drg_falling``
+     - ``drg_amplitude``
+     - DRG falling-ramp parameters: limit code, dwell enable, ramp clock,
+       rate of change.
+
+   * - ``out_altcurrent140``
+     - ``ram``
+     - ``phy``
+     - RAM playback: enable, frequency, phase and sampling frequency for
+       the active profile. See `RAM mode`_.
+
+   * - ``out_altcurrent150``
+     - ``osk``
+     - ``phy``
+     - Output shift keying (OSK): enable, amplitude code, ramp rate,
+       rate of change. See `Output Shift Keying (OSK)`_.
+
+DDS modes
+=========
+
+The AD9910 supports multiple modes of operation that can be configured
+independently or in combination. Each DDS core parameter (frequency, phase
+and amplitude) can come from different sources, but only one is active at a
+time. This activation depends on a priority list, which is based on the enable
+and destination configurations for such modes. The following tables are
+extracted from the AD9910 datasheet and summarize the control parameters for
+each mode and their priority when multiple sources are enabled simultaneously:
+
+.. flat-table:: DDS Frequency Control
+   :header-rows: 1
+
+   * - Priority
+     - Data Source
+     - Conditions
+
+   * - Highest Priority
+     - RAM
+     - RAM enabled and data destination is frequency
+
+   * -
+     - DRG
+     - DRG enabled and data destination is frequency
+
+   * -
+     - Parallel data and Frequency Tuning Word, FTW (frequency_offset)
+     - Parallel data port enabled and data destination is frequency
+
+   * -
+     - FTW register (frequency)
+     - RAM enabled and data destination is not frequency
+
+   * - Lowest Priority
+     - FTW (frequency) in single tone channel for the active profile
+     - All other cases
+
+.. flat-table:: DDS Phase Control
+   :header-rows: 1
+
+   * - Priority
+     - Data Source
+     - Conditions
+
+   * - Highest Priority
+     - RAM
+     - RAM enabled and data destination is phase or polar
+
+   * -
+     - DRG
+     - DRG enabled and data destination is phase
+
+   * -
+     - Parallel data port
+     - Parallel data port enabled and data destination is phase
+
+   * -
+     - Parallel data port and Phase Offset Word, POW register LSBs (phase_offset)
+     - Parallel data port enabled and data destination is polar
+
+   * -
+     - POW register (phase)
+     - RAM enabled and destination is not phase nor polar
+
+   * - Lowest Priority
+     - POW (phase) in single tone channel for the active profile
+     - All other cases
+
+.. flat-table:: DDS Amplitude Control
+   :header-rows: 1
+
+   * - Priority
+     - Data Source
+     - Conditions
+
+   * - Highest Priority
+     - Amplitude Scale Factor, ASF register and OSK generator
+     - OSK enabled
+
+   * -
+     - RAM
+     - RAM enabled and data destination is amplitude or polar
+
+   * -
+     - DRG
+     - DRG enabled and data destination is amplitude
+
+   * -
+     - Parallel data port
+     - Parallel data port enabled and data destination is amplitude
+
+   * -
+     - Parallel data port and ASF register LSBs (scale_offset)
+     - Parallel data port enabled and data destination is polar
+
+   * - Lowest Priority
+     - ASF (scale) in single tone channel for the active profile
+     - (Amplitude scale is already enabled by default)
+
+While debugging or testing, the debug attributes ``frequency_source``,
+``phase_source`` and ``amplitude_source`` can be used to read the label of
+the channel that is actively controlling the correspondent DDS parameter,
+which reflects the priority list described above.
+
+Single Tone mode
+----------------
+
+Single tone is the baseline operating mode. The ``profileY`` channels
+provide enable, frequency, phase and amplitude control:
+
+.. flat-table::
+   :header-rows: 1
+
+   * - Attribute
+     - Unit
+     - Description
+
+   * - ``en``
+     - boolean (0 or 1)
+     - Enable/disable profile Y. Only one profile can be active at a
+       time. When enabling a profile it disables the current active profile.
+       Disabling an active profile brings the device to a powered down state.
+
+   * - ``frequency``
+     - Hz
+     - Output frequency. Range :math:`[0, f_{SYSCLK}/2)`. Stored in the
+       profile's frequency tuning word (FTW).
+
+   * - ``phase``
+     - rad
+     - Phase offset. Range :math:`[0, 2\pi)`. Stored in the profile's phase
+       offset word (POW).
+
+   * - ``raw``
+     - integer
+     - Amplitude scale factor code. Range :math:`[0, 16383]`. Stored in the
+       profile's amplitude scale factor (ASF) register. The physical output
+       amplitude is ``raw * scale`` where ``scale`` is read from the ``phy``
+       channel.
+
+Profile switching is allowed while RAM mode is enabled. In that case single
+tone parameters are stored in a shadow register and are not written to
+hardware until RAM mode is disabled.
+
+Usage examples
+^^^^^^^^^^^^^^
+
+Configure a 100 MHz tone in profile 2 and set it as the active profile:
+
+.. code-block:: bash
+
+  echo 100000000 > /sys/bus/iio/devices/iio\:device0/out_altcurrent112_frequency
+  echo 0 > /sys/bus/iio/devices/iio\:device0/out_altcurrent112_phase
+  echo 16383 > /sys/bus/iio/devices/iio\:device0/out_altcurrent112_raw
+
+  # Activate profile 2
+  echo 1 > /sys/bus/iio/devices/iio\:device0/out_altcurrent112_en
+
+Read back the current single tone frequency:
+
+.. code-block:: bash
+
+  cat /sys/bus/iio/devices/iio\:device0/out_altcurrent112_frequency
+
+Parallel Port mode
+------------------
+
+The parallel port allows real-time modulation of DDS parameters through a
+16-bit external data bus. The driver exposes separate typed channels for each
+modulation target.
+
+Non-polar modulation
+^^^^^^^^^^^^^^^^^^^^
+
+In non-polar mode each DDS parameter is controlled by an independent 16-bit bus
+input. The parallel port channels expose the resolution and base offset of their
+respective bus inputs:
+
+.. flat-table::
+   :header-rows: 1
+
+   * - Channel
+     - Attribute
+     - Unit
+     - Description
+
+   * - ``out_phase120``
+     - ``scale``
+     - rad
+     - Phase resolution per parallel bus LSB. Fixed at :math:`\pi / 2^{15}`
+       rad/LSB (full 16-bit POW resolution).
+
+   * - ``out_frequency120``
+     - ``scale``
+     - Hz
+     - Outputs the frequency scale evaluated as
+       :math:`f_{SYSCLK} \cdot FM / 2^{32}`. Assuming that :math:`f_{SYSCLK}` is
+       fixed, it is used to configure the modulation gain :math:`FM`, which is a
+       power-of-2 multiplier in range :math:`[1, 32768]`. Writing to this
+       attribute rounds up to the nearest :math:`FM` power of 2.
+
+   * - ``out_frequency120``
+     - ``offset``
+     - Hz
+     - Outputs the frequency offset in raw units evaluated as :math:`FTW / FM`.
+       Assuming that :math:`FM` is fixed, it is used to configure the FTW
+       register, which is a 32-bit unsigned integer.
+
+Polar modulation
+^^^^^^^^^^^^^^^^
+
+In polar mode a single 16-bit bus word carries both amplitude (high byte)
+and phase (low byte). The ``parallel_polar_amplitude`` and
+``parallel_polar_phase`` channels configure the bias applied to the low-order
+bits of the ASF and POW registers respectively:
+
+.. flat-table::
+   :header-rows: 1
+
+   * - Channel
+     - Attribute
+     - Unit
+     - Description
+
+   * - ``out_altcurrent121``
+     - ``scale``
+     - mA/LSB
+     - Full-scale amplitude resolution (read-only, fixed at :math:`I_{FS} / 2^{8}`).
+
+   * - ``out_altcurrent121``
+     - ``offset``
+     - fractional (raw units)
+     - Amplitude bias. Lower 6 bits of ASF register. Range :math:`[0, 1)`.
+
+   * - ``out_phase121``
+     - ``scale``
+     - rad/LSB
+     - Phase resolution (read-only, fixed at :math:`\pi / 2^{7}`).
+
+   * - ``out_phase121``
+     - ``offset``
+     - fractional (raw units)
+     - Phase bias. Lower 8 bits of POW register. Range :math:`[0, 1)`.
+
+Usage examples
+^^^^^^^^^^^^^^
+
+Set parallel port frequency modulation with a modulation gain of 16 and a 50 MHz
+offset:
+
+.. code-block:: bash
+
+  # f_SYSCLK = 1 GHz, FM = 16
+  # frequency scale = f_SYSCLK * FM / 2^32 = 3.725290298
+  echo 3.725290298 > /sys/bus/iio/devices/iio\:device0/out_frequency120_scale
+  # frequency offset = 50 MHz / scale = 50e6 / 13421772.8
+  echo 13421772.8 > /sys/bus/iio/devices/iio\:device0/out_frequency120_offset
+
+One should choose a frequency scale that allows all the desired frequencies
+to be represented in the 16-bit bus range, i.e.,
+:math:`scale = (f_{max} - f_{min}) / 2^{16}`.
+
+
+Digital ramp generator (DRG)
+----------------------------
+
+The DRG produces linear frequency, phase or amplitude sweeps using dedicated
+hardware. The active ramp target (destination) is selected by enabling the
+corresponding typed channel at channel number 130:
+
+- ``out_frequency130`` (label ``drg_frequency``) — ramp targets frequency
+- ``out_phase130`` (label ``drg_phase``) — ramp targets phase
+- ``out_altcurrent130`` (label ``drg_amplitude``) — ramp targets amplitude
+
+Writing ``en=1`` to one of these channels enables the DRG and switches its
+destination. Writing ``en=0`` disables the DRG if the channel is the current
+active destination; writing to an already-inactive destination is a no-op.
+
+Each destination channel also exposes a read-only ``scale`` attribute
+reporting the physical quantity per ramp register LSB, which allows converting
+raw limit codes to physical values.
+
+The two ramp channels ``out_altcurrent131`` (``drg_rising``) and
+``out_altcurrent132`` (``drg_falling``) configure ascending and descending
+ramp parameters independently.
+
+Destination channel attributes
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+.. flat-table::
+   :header-rows: 1
+
+   * - Attribute
+     - Unit
+     - Description
+
+   * - ``en``
+     - boolean
+     - Enable the DRG with this channel as the active destination. Only one
+       destination can be active at a time.
+
+   * - ``scale``
+     - Hz/LSB, rad/LSB or mA/LSB
+     - Read-only. Physical quantity per raw units. Multiply a ramp
+       rising/falling channel ``raw`` value by this scale to get the physical
+       ramp target.
+
+Ramp channel attributes
+^^^^^^^^^^^^^^^^^^^^^^^
+
+.. flat-table::
+   :header-rows: 1
+
+   * - Attribute
+     - Unit
+     - Description
+
+   * - ``dwell_en``
+     - boolean
+     - Enable dwell at the ramp limit. When disabled, the ramp
+       auto-transitions at this limit without waiting for the DRCTL pin.
+       Disabling both creates a bidirectional continuous ramp (triangular
+       pattern). Other combinations create single-shot ramps at the DRCTL
+       pin transition.
+
+   * - ``raw``
+     - integer (64-bit)
+     - Ramp limit expressed as a raw DRG register code in
+       :math:`[0, 2^{32}-1]`. The physical value is ``raw * scale`` where
+       ``scale`` is read from the active destination channel.
+
+   * - ``sampling_frequency``
+     - Hz
+     - Ramp clock rate. Controlled by an integer divider; the written value
+       is adjusted to the nearest supported rate.
+
+   * - ``raw_roc``
+     - /s
+     - Rate of change. Number of register codes advanced per second, computed
+       from the hardware step size and the current ramp clock. Writing
+       requires ``sampling_frequency`` to be configured first.
+
+Usage examples
+^^^^^^^^^^^^^^
+
+Configure a frequency sweep from 40 MHz to 60 MHz with a rate of change of
+25 GHz/s:
+
+.. code-block:: bash
+
+  # Disable dwell on both limits for a bidirectional continuous ramp
+  echo 0 > /sys/bus/iio/devices/iio\:device0/out_altcurrent131_dwell_en
+  echo 0 > /sys/bus/iio/devices/iio\:device0/out_altcurrent132_dwell_en
+
+  # Set ramp rate at 250 MHz
+  echo 250000000 > /sys/bus/iio/devices/iio\:device0/out_altcurrent131_sampling_frequency
+  echo 250000000 > /sys/bus/iio/devices/iio\:device0/out_altcurrent132_sampling_frequency
+
+  # read the frequency scale to convert physical values to raw units
+  cat /sys/bus/iio/devices/iio\:device0/out_frequency130_scale
+  0.232830643650
+
+  # 40 MHz / 0.232830643650 = 171798692
+  echo 171798692 > /sys/bus/iio/devices/iio\:device0/out_altcurrent131_raw
+  # 60 MHz / 0.232830643650 = 257698038
+  echo 257698038 > /sys/bus/iio/devices/iio\:device0/out_altcurrent132_raw
+
+  # 25 GHz/s / 0.232830643650 = 107374182402
+  echo 107374182402 > /sys/bus/iio/devices/iio\:device0/out_altcurrent131_raw_roc
+  echo 107374182402 > /sys/bus/iio/devices/iio\:device0/out_altcurrent132_raw_roc
+
+  # Enable the DRG with frequency as the destination
+  echo 1 > /sys/bus/iio/devices/iio\:device0/out_frequency130_en
+
+RAM mode
+--------
+
+The AD9910 contains a 1024 x 32-bit RAM that can be loaded with waveform data
+and played back to modulate frequency, phase, amplitude, or polar (phase +
+amplitude) parameters.
+
+RAM control channel attributes
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+.. flat-table::
+   :header-rows: 1
+
+   * - Attribute
+     - Unit
+     - Description
+
+   * - ``en``
+     - boolean
+     - Enable/disable RAM playback. Toggling swaps profile registers between
+       single tone and RAM configurations across all 8 profiles.
+
+   * - ``frequency``
+     - Hz
+     - Frequency tuning word used as the single tone frequency when
+       RAM destination is not ``frequency``. Range: :math:`[0, f_{SYSCLK}/2)`.
+
+   * - ``phase``
+     - rad
+     - Phase offset word used as the single tone phase when RAM destination
+       is not ``phase``. Range: :math:`[0, 2\pi)`.
+
+   * - ``sampling_frequency``
+     - Hz
+     - RAM playback step rate of the active profile, which controls how fast
+       the address counter advances. Controlled by an integer divider; the
+       written value is adjusted to the nearest supported rate.
+
+Loading RAM data
+^^^^^^^^^^^^^^^^
+
+RAM data is loaded through the firmware upload framework. The driver registers
+a firmware upload sysfs entry named ``iio_deviceX:ram``. The firmware data
+follows a binary format (version 1) with an 80-byte header followed by data
+words. All fields are big-endian.
+
+.. flat-table:: RAM firmware header (80 bytes)
+   :header-rows: 1
+
+   * - Offset
+     - Size
+     - Field
+     - Description
+
+   * - 0
+     - 4
+     - ``magic``
+     - Magic number: ``0x00AD9910``
+
+   * - 4
+     - 2
+     - ``version``
+     - Format version: ``0x0001``
+
+   * - 6
+     - 2
+     - ``wcount``
+     - Number of 32-bit RAM data words (0--1024)
+
+   * - 8
+     - 4
+     - ``crc``
+     - CRC32 checksum over ``cfr1``, ``profiles`` and ``words``
+
+   * - 12
+     - 4
+     - ``cfr1``
+     - CFR1 register value. Only RAM-relevant bits are used:
+       bits [30:29] set data destination (00: frequency, 01: phase,
+       10: amplitude, 11: polar); bits [20:17] set internal profile
+       control (see datasheet Table 14)
+
+   * - 16
+     - 64
+     - ``profiles[0..7]``
+     - 8 sets of 8-byte RAM profile configurations (see below)
+
+   * - 80
+     - 4 x wcount
+     - ``words[]``
+     - RAM data words in reverse order
+
+Each 8-byte profile entry contains:
+
+.. flat-table:: RAM profile entry (8 bytes)
+   :header-rows: 1
+
+   * - Bits
+     - Field
+     - Description
+
+   * - [55:40]
+     - Address step rate
+     - Controls playback speed for this profile
+
+   * - [39:30]
+     - End address
+     - Last RAM address for this profile
+
+   * - [23:14]
+     - Start address
+     - First RAM address for this profile
+
+   * - [5]
+     - No-dwell high
+     - No-dwell at high limit (ramp-up mode)
+
+   * - [3]
+     - Zero-crossing
+     - Zero-crossing enable (direct-switch mode)
+
+   * - [2:0]
+     - Operating mode
+     - 000: direct switch, 001: ramp-up, 010: bidirectional,
+       011: bidirectional continuous, 100: ramp-up continuous
+
+Usage examples
+^^^^^^^^^^^^^^
+
+Configure RAM mode with firmware data and enable it:
+
+.. code-block:: bash
+
+  # Load RAM data via firmware upload
+  echo 1 > /sys/class/firmware/iio\:device0\:ram/loading
+  cat ad9910-ram.bin > /sys/class/firmware/iio\:device0\:ram/data
+  echo 0 > /sys/class/firmware/iio\:device0\:ram/loading
+
+  # Enable RAM mode
+  echo 1 > /sys/bus/iio/devices/iio\:device0/out_altcurrent140_en
+
+Output Shift Keying (OSK)
+-------------------------
+
+OSK controls the output amplitude envelope, allowing the output to be ramped
+on/off rather than switched abruptly.
+
+.. flat-table::
+   :header-rows: 1
+
+   * - Attribute
+     - Unit
+     - Description
+
+   * - ``en``
+     - boolean (0 or 1)
+     - Enable/disable OSK.
+
+   * - ``raw``
+     - integer
+     - Target amplitude code. 14-bit ASF field. Range: :math:`[0, 16383]`.
+       The physical output amplitude is ``raw * scale`` where ``scale`` is read
+       from the ``phy`` channel.
+
+   * - ``raw_roc``
+     - /s
+     - Amplitude ramp rate. Writing a non-zero value enables automatic OSK
+       and selects the closest hardware step size. Writing ``0`` disables
+       automatic ramping (manual control via ``raw``). Writing the maximum
+       available value enables pin-controlled immediate transition.
+
+   * - ``raw_roc_available``
+     - /s
+     - Lists the available ``raw_roc`` values based on the current
+       ``sampling_frequency``. The first value is always ``0`` (disabled) and
+       the last value corresponds to pin-controlled immediate mode.
+
+   * - ``sampling_frequency``
+     - Hz
+     - OSK ramp clock. Controlled by an integer divider; the written value
+       is adjusted to the nearest supported rate.
+
+Usage examples
+^^^^^^^^^^^^^^
+
+Enable OSK with automatic ramping:
+
+.. code-block:: bash
+
+  # Set ramp rate 1MHz
+  echo 1000000 > /sys/bus/iio/devices/iio\:device0/out_altcurrent150_sampling_frequency
+
+  # Check available rate of change values
+  cat /sys/bus/iio/devices/iio\:device0/out_altcurrent150_raw_roc_available
+  0 1000000 2000000 4000000 8000000 16383000000
+
+  # Enable automatic OSK with a rate of change of 8000000 raw units/s
+  echo 8000000 > /sys/bus/iio/devices/iio\:device0/out_altcurrent150_raw_roc
+
+  # Enable OSK
+  echo 1 > /sys/bus/iio/devices/iio\:device0/out_altcurrent150_en
+
+Enable pin-controlled immediate OSK:
+
+.. code-block:: bash
+
+  # Enable OSK in manual mode (no ramp)
+  echo 0 > /sys/bus/iio/devices/iio\:device0/out_altcurrent150_raw_roc
+  echo 1 > /sys/bus/iio/devices/iio\:device0/out_altcurrent150_en
+
+  # Set target amplitude to full scale
+  echo 16383 > /sys/bus/iio/devices/iio\:device0/out_altcurrent150_raw
+
+Physical channel
+================
+
+The ``phy`` channel provides device-level control:
+
+.. flat-table::
+   :header-rows: 1
+
+   * - Attribute
+     - Unit
+     - Description
+
+   * - ``sampling_frequency``
+     - Hz
+     - System clock (SYSCLK) frequency. When the internal PLL is enabled
+       (via the ``adi,pll-enable`` devicetree property), configures the PLL
+       multiplier (Range: :math:`[420, 1000]` MHz). Without PLL, the reference
+       clock can only be divided by 2.
+
+   * - ``scale``
+     - mA/LSB
+     - Full-scale DAC output current per amplitude code LSB, which is evaluated
+       as :math:`I_{FS}/2^{14}`. Shared across all ``altcurrent`` channels.
+       Setting this attribute reconfigures the auxiliary DAC full-scale code and
+       updates the effective amplitude resolution for single tone profiles,
+       DRG amplitude ramps and OSK.
+
+   * - ``powerdown``
+     - boolean (0 or 1)
+     - Software power-down. Writing 1 powers down the digital core, DAC,
+       reference clock input and auxiliary DAC simultaneously.
+
+Usage examples
+--------------
+
+Set the system clock to 1 GHz:
+
+.. code-block:: bash
+
+  echo 1000000000 > /sys/bus/iio/devices/iio\:device0/out_altcurrent100_sampling_frequency
+
+Read current system clock frequency:
+
+.. code-block:: bash
+
+  cat /sys/bus/iio/devices/iio\:device0/out_altcurrent100_sampling_frequency
+
+Power down the device:
+
+.. code-block:: bash
+
+  echo 1 > /sys/bus/iio/devices/iio\:device0/out_altcurrent100_powerdown
\ No newline at end of file
diff --git a/Documentation/iio/index.rst b/Documentation/iio/index.rst
index b02b879b053a..4c30ef033685 100644
--- a/Documentation/iio/index.rst
+++ b/Documentation/iio/index.rst
@@ -30,6 +30,7 @@ Industrial I/O Kernel Drivers
    ad7606
    ad7625
    ad7944
+   ad9910
    ade9000
    adf41513
    adis16475
diff --git a/MAINTAINERS b/MAINTAINERS
index a76a15f02183..38e7fd5e3c34 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -1652,6 +1652,7 @@ S:	Supported
 W:	https://ez.analog.com/linux-software-drivers
 F:	Documentation/ABI/testing/sysfs-bus-iio-frequency-ad9910
 F:	Documentation/devicetree/bindings/iio/frequency/adi,ad9910.yaml
+F:	Documentation/iio/ad9910.rst
 F:	drivers/iio/frequency/ad9910.c
 
 ANALOG DEVICES INC MAX22007 DRIVER

-- 
2.43.0