docs: iio: new docs for ad7944 driver
This adds a new page to document how to use the ad7944 ADC driver. Signed-off-by: David Lechner <dlechner@baylibre.com> Link: https://lore.kernel.org/r/20240322-mainline-ad7944-doc-v2-2-0923d35d5596@baylibre.com Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
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David Lechner
Jonathan Cameron
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.. SPDX-License-Identifier: GPL-2.0-only
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=============
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AD7944 driver
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=============
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ADC driver for Analog Devices Inc. AD7944 and similar devices. The module name
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is ``ad7944``.
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Supported devices
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=================
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The following chips are supported by this driver:
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* `AD7944 <https://www.analog.com/AD7944>`_
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* `AD7985 <https://www.analog.com/AD7985>`_
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* `AD7986 <https://www.analog.com/AD7986>`_
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Supported features
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==================
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SPI wiring modes
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----------------
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The driver currently supports two of the many possible SPI wiring configurations.
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CS mode, 3-wire, without busy indicator
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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.. code-block::
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+-------------+
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+--------------------| CS |
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v | |
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VIO +--------------------+ | HOST |
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| | CNV | | |
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+--->| SDI AD7944 SDO |-------->| SDI |
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| SCK | | |
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+--------------------+ | |
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^ | |
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+--------------------| SCLK |
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+-------------+
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To select this mode in the device tree, set the ``adi,spi-mode`` property to
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``"single"`` and omit the ``cnv-gpios`` property.
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CS mode, 4-wire, without busy indicator
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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.. code-block::
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+-------------+
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+-----------------------------------| CS |
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| | |
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| +--------------------| GPIO |
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| v | |
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| +--------------------+ | HOST |
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| | CNV | | |
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+--->| SDI AD7944 SDO |-------->| SDI |
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| SCK | | |
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+--------------------+ | |
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^ | |
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+--------------------| SCLK |
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+-------------+
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To select this mode in the device tree, omit the ``adi,spi-mode`` property and
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provide the ``cnv-gpios`` property.
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Reference voltage
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-----------------
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All 3 possible reference voltage sources are supported:
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- Internal reference
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- External 1.2V reference and internal buffer
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- External reference
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The source is determined by the device tree. If ``ref-supply`` is present, then
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the external reference is used. If ``refin-supply`` is present, then the internal
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buffer is used. If neither is present, then the internal reference is used.
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Unimplemented features
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----------------------
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- ``BUSY`` indication
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- ``TURBO`` mode
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- Daisy chain mode
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Device attributes
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=================
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There are two types of ADCs in this family, pseudo-differential and fully
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differential. The channel name is different depending on the type of ADC.
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Pseudo-differential ADCs
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------------------------
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AD7944 and AD7985 are pseudo-differential ADCs and have the following attributes:
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+---------------------------------------+--------------------------------------------------------------+
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| Attribute | Description |
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+=======================================+==============================================================+
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| ``in_voltage0_raw`` | Raw ADC voltage value (*IN+* referenced to ground sense). |
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+---------------------------------------+--------------------------------------------------------------+
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| ``in_voltage0_scale`` | Scale factor to convert raw value to mV. |
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+---------------------------------------+--------------------------------------------------------------+
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Fully-differential ADCs
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-----------------------
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AD7986 is a fully-differential ADC and has the following attributes:
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+---------------------------------------+--------------------------------------------------------------+
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| Attribute | Description |
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+=======================================+==============================================================+
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| ``in_voltage0-voltage1_raw`` | Raw ADC voltage value (*IN+* - *IN-*). |
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+---------------------------------------+--------------------------------------------------------------+
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| ``in_voltage0-voltage1_scale`` | Scale factor to convert raw value to mV. |
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+---------------------------------------+--------------------------------------------------------------+
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Device buffers
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==============
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This driver supports IIO triggered buffers.
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See :doc:`iio_devbuf` for more information.
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@ -16,6 +16,7 @@ Industrial I/O Kernel Drivers
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.. toctree::
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:maxdepth: 1
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ad7944
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adis16475
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bno055
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ep93xx_adc
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@ -448,6 +448,7 @@ R: David Lechner <dlechner@baylibre.com>
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S: Supported
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W: https://ez.analog.com/linux-software-drivers
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F: Documentation/devicetree/bindings/iio/adc/adi,ad7944.yaml
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F: Documentation/iio/ad7944.rst
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F: drivers/iio/adc/ad7944.c
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ADAFRUIT MINI I2C GAMEPAD
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