Re: [PATCH v2 5/6] docs: iio: add documentation for adf41513 driver

Jonathan Cameron
2025-12-21T18:00:28Z

On Fri, 19 Dec 2025 12:34:52 +0000
Rodrigo Alencar via B4 Relay <devnull+rodrigo.alencar.analog.com@kernel.org> wrote:

> From: Rodrigo Alencar <rodrigo.alencar@analog.com>
>
> add documentation for ADF41513 driver which describes the device
Add

> driver files and shows how userspace may consume the ABI for various
> tasks
.

>
> Signed-off-by: Rodrigo Alencar <rodrigo.alencar@analog.com>
> ---
> Documentation/iio/adf41513.rst | 255 +++++++++++++++++++++++++++++++++++++++++
> Documentation/iio/index.rst | 1 +
> MAINTAINERS | 1 +
> 3 files changed, 257 insertions(+)
>
> diff --git a/Documentation/iio/adf41513.rst b/Documentation/iio/adf41513.rst
> new file mode 100644
> index 000000000000..568e71bc21e4
> --- /dev/null
> +++ b/Documentation/iio/adf41513.rst
> @@ -0,0 +1,255 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +===============
> +ADF41513 driver
> +===============
> +
> +This driver supports Analog Devices' ADF41513 and ADF41510 PLL frequency
> +synthesizers on SPI bus.
Avoid lists of part numbers inline with text. Those become very noisy
if more parts are added in future. Given next block has bullet point list
of parts no need to mention them here. Instead use
ADF41513 and similar SPI PLL frequency synthesizers.
> +
> +1. Supported devices
> +====================
> +
> +* `ADF41510 <https://www.analog.com/ADF41510>`_
> +* `ADF41513 <https://www.analog.com/ADF41513>`_
> +
> +The ADF41513 is an ultralow noise frequency synthesizer that can be used to
> +implement local oscillators (LOs) as high as 26.5 GHz in the upconversion and
> +downconversion sections of wireless receivers and transmitters. The ADF41510
> +is a similar device that supports frequencies up to 10 GHz.
> +
> +Both devices support integer-N and fractional-N operation modes, providing
> +excellent phase noise performance and flexible frequency generation
> +capabilities.
> +
> +Key Features:
> +
> +- **ADF41513**: 1 GHz to 26.5 GHz frequency range
> +- **ADF41510**: 1 GHz to 10 GHz frequency range
Keep them in alphanumeric order. Makes it easier to add more parts by
keeping the placement obvious.

> +- Integer-N and fractional-N operation modes
> +- Ultra-low phase noise (-235 dBc/Hz integer-N, -231 dBc/Hz fractional-N)
> +- High maximum PFD frequency (250 MHz integer-N, 125 MHz fractional-N)
> +- 25-bit fixed modulus or 49-bit variable modulus fractional modes
> +- Programmable charge pump currents with 16x range
> +- Digital lock detect functionality
> +- Phase resync capability for consistent output phase
> +
> +2. Device attributes
> +====================
> +
> +The ADF41513 driver provides the following IIO extended attributes for
> +frequency control and monitoring:
> +
> +Each IIO device has a device folder under ``/sys/bus/iio/devices/iio:deviceX``,
> +where X is the IIO index of the device. Under these folders reside a set of
> +device files that provide access to the synthesizer's functionality.
> +
> +The following table shows the ADF41513 related device files:
> +
> ++----------------------+-------------------------------------------------------+
> +| Device file | Description |
> ++======================+=======================================================+
> +| frequency | RF output frequency control and readback (Hz) |
> ++----------------------+-------------------------------------------------------+
> +| frequency_resolution | Target frequency resolution control (Hz) |
> ++----------------------+-------------------------------------------------------+
> +| refin_frequency | Reference input frequency control and readback (Hz) |
> ++----------------------+-------------------------------------------------------+
> +| powerdown | Power management control (0=active, 1=power down) |
> ++----------------------+-------------------------------------------------------+
> +| phase | RF output phase adjustment and readback (degrees) |
> ++----------------------+-------------------------------------------------------+
> +
> +2.1 Frequency Control
> +----------------------
> +
> +The ``frequency`` attribute controls the RF output frequency with sub-Hz
> +precision. The driver automatically selects between integer-N and fractional-N
> +modes to achieve the requested frequency with the best possible phase noise
> +performance.
> +
> +**Supported ranges:**
> +
> +- **ADF41513**: 1,000,000,000 Hz to 26,500,000,000 Hz (1 GHz to 26.5 GHz)
> +- **ADF41510**: 1,000,000,000 Hz to 10,000,000,000 Hz (1 GHz to 10 GHz)
Alpha numeric order here as well.

> +
> +The frequency is specified in Hz, for sub-Hz precision use decimal notation.
> +For example, 12.102 GHz would be written as "12102000000.000000".
> +
> +2.2 Frequency Resolution Control
> +--------------------------------
> +
> +The ``frequency_resolution`` attribute controls the target frequency resolution
> +that the driver attempts to achieve. This affects the choice between integer-N
> +and fractional-N modes, including fixed modulus (25-bit) and variable modulus
> +(49-bit) fractional-N modes:
> +
> +- **Integer-N**: Resolution = f_PFD
> +- **Fixed modulus**: Resolution = f_PFD / 2^25 (~3 Hz with 100 MHz PFD)
> +- **Variable modulus**: Resolution = f_PFD / 2^49 (µHz resolution possible)
> +
> +Default resolution is 1 Hz (1,000,000 µHz).
> +
> +2.3 Reference Input Control
> +---------------------------
> +
> +The ``refin_frequency`` attribute allows control of the reference input
> +frequency when using a programmable reference clock. The supported range is
> +10 MHz to 800 MHz.

I'm not really sure why need this as opposed to having a standard clock
provide it. What's the use case?

> +
> +2.4 Power Management
> +--------------------
> +
> +The ``powerdown`` attribute provides software power control:
> +
> +- **0**: Device active and operational
> +- **1**: Device in power-down mode (low power consumption)

This one is fairly standard for DACs etc. I'd not necessarily bother
documenting it specifically here.

> +
> +2.5 Phase adjustment
> +--------------------
> +
> +The ``phase`` attribute allows adjustment of the output phase in degrees.

As per driver feedback, I don't think this is compliant with existing ABI.

> +Setting this attribute enables phase adjustment. It can be set from 0 to 360
> +degrees. Reading this attribute returns the current phase offset of the output
> +signal. To create a consistent phase relationship with the reference signal,
> +the phase resync feature needs to be enabled by setting a non-zero value to the
> +``adi,phase-resync-period-ns`` device property, which triggers a phase
> +resynchronization after locking is achieved.
> +
> +3. Operating modes
> +==================
> +
> +3.1 Integer-N Mode
> +------------------
> +
> +When the requested frequency can be achieved as an integer multiple of the PFD
> +frequency (within the specified resolution tolerance), the driver automatically
> +selects integer-N mode for optimal phase noise performance.
> +
> +In integer-N mode:
> +
> +- Phase noise: -235 dBc/Hz normalized floor
> +- Frequency resolution: f_PFD (same as PFD frequency)
> +- Maximum PFD frequency: 250 MHz
> +- Bleed current: Disabled for best performance
> +
> +3.2 Fractional-N Mode
> +---------------------
> +
> +When sub-integer frequency steps are required, the driver automatically selects
> +fractional-N mode using either fixed or variable modulus.
> +
> +**Fixed Modulus (25-bit)**:
> +
> +- Used when variable modulus is not required
> +- Resolution: f_PFD / 2^25
> +- Simpler implementation, faster settling
> +
> +**Variable Modulus (49-bit)**:
> +
> +- Used for maximum resolution requirements
> +- Resolution: f_PFD / 2^49 (theoretical)
> +- Exact frequency synthesis capability
> +
> +In fractional-N mode:
> +
> +- Phase noise: -231 dBc/Hz normalized floor
> +- Maximum PFD frequency: 125 MHz
> +- Bleed current: Automatically enabled and optimized
> +- Dithering: Enabled to reduce fractional spurs
> +
> +3.3 Automatic Mode Selection
> +----------------------------
> +
> +The driver automatically selects the optimal operating mode based on:
> +
> +1. **Frequency accuracy requirements**: Determined by frequency_resolution setting
> +2. **Phase noise optimization**: Integer-N preferred when possible
> +3. **PFD frequency constraints**: Different limits for integer vs fractional modes
> +4. **Prescaler selection**: Automatic 4/5 vs 8/9 prescaler selection based on frequency
> +
> +4. Usage examples
> +=================
> +
> +4.1 Basic Frequency Setting
> +----------------------------
> +
> +Set output frequency to 12.102 GHz:
> +
> +.. code-block:: bash
> +
> + root:/sys/bus/iio/devices/iio:device0> echo 12102000000 > out_altvoltage0_frequency
> +
> +Read current frequency:
> +
> +.. code-block:: bash
> +
> + root:/sys/bus/iio/devices/iio:device0> cat out_altvoltage0_frequency
> + 12101999999.582767
> +
> +4.2 High Resolution Frequency Control
> +-------------------------------------
> +
> +Configure for sub-Hz resolution and set a precise frequency:
> +
> +.. code-block:: bash
> +
> + # Set resolution to 0.1 Hz (100,000 µHz)
> + root:/sys/bus/iio/devices/iio:device0> echo 0.1 > out_altvoltage0_frequency_resolution
> +
> + # Set frequency to 12.102 GHz (1 µHz precision)
> + root:/sys/bus/iio/devices/iio:device0> echo 12102000000 > out_altvoltage0_frequency
> + root:/sys/bus/iio/devices/iio:device0> cat out_altvoltage0_frequency
> + 12101999999.980131
> +
> +4.3 Reference Frequency Control
> +-------------------------------
> +
> +Change reference input frequency (if using programmable reference):
> +
> +.. code-block:: bash
> +
> + # Set reference to 122.88 MHz
> + root:/sys/bus/iio/devices/iio:device0> echo 122880000 > out_altvoltage0_refin_frequency
> +
> + # Verify the change
> + root:/sys/bus/iio/devices/iio:device0> cat out_altvoltage0_refin_frequency
> + 122880000
> +
> +4.4 Power Management
> +--------------------
> +
> +Power down the device:
> +
> +.. code-block:: bash
> +
> + root:/sys/bus/iio/devices/iio:device0> echo 1 > out_altvoltage0_powerdown
> +
> + # Power back up
> + root:/sys/bus/iio/devices/iio:device0> echo 0 > out_altvoltage0_powerdown

I'd skip this section as being very standard.

> +
> +4.5 PFD Frequency Monitoring
> +----------------------------
> +
> +Read the current PFD frequency:
> +
> +.. code-block:: bash
> +
> + root:/sys/bus/iio/devices/iio:device0> cat out_altvoltage0_pfd_frequency

This one isn't standard ABI or in your ABI doc.
Perhaps drop for now?

> + 100000000.000000
> +
> +This shows the PFD is operating at 100 MHz, which means the frequency resolution
> +in integer-N mode would be 100 MHz steps.
> +
> +4.6 Monitor Lock Status
> +-----------------------
> +
> +When lock detect GPIO is configured, check if PLL is locked:
> +
> +.. code-block:: bash
> +
> + # Read frequency - will return error if not locked
> + root:/sys/bus/iio/devices/iio:device0> cat out_altvoltage0_frequency
> +
> +If the PLL is not locked, the frequency read will return ``-EBUSY`` (Device or
> +resource busy).