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docs: iio: new docs for ad7944 driver

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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 2024-03-22 16:52:14 -05:00 committed by Jonathan Cameron
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130
Documentation/iio/ad7944.rst Normal file
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.. SPDX-License-Identifier: GPL-2.0-only
=============
AD7944 driver
=============
ADC driver for Analog Devices Inc. AD7944 and similar devices. The module name
is ``ad7944``.
Supported devices
=================
The following chips are supported by this driver:
* `AD7944 <https://www.analog.com/AD7944>`_
* `AD7985 <https://www.analog.com/AD7985>`_
* `AD7986 <https://www.analog.com/AD7986>`_
Supported features
==================
SPI wiring modes
----------------
The driver currently supports two of the many possible SPI wiring configurations.
CS mode, 3-wire, without busy indicator
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
.. code-block::
+-------------+
+--------------------| CS |
v | |
VIO +--------------------+ | HOST |
| | CNV | | |
+--->| SDI AD7944 SDO |-------->| SDI |
| SCK | | |
+--------------------+ | |
^ | |
+--------------------| SCLK |
+-------------+
To select this mode in the device tree, set the ``adi,spi-mode`` property to
``"single"`` and omit the ``cnv-gpios`` property.
CS mode, 4-wire, without busy indicator
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
.. code-block::
+-------------+
+-----------------------------------| CS |
| | |
| +--------------------| GPIO |
| v | |
| +--------------------+ | HOST |
| | CNV | | |
+--->| SDI AD7944 SDO |-------->| SDI |
| SCK | | |
+--------------------+ | |
^ | |
+--------------------| SCLK |
+-------------+
To select this mode in the device tree, omit the ``adi,spi-mode`` property and
provide the ``cnv-gpios`` property.
Reference voltage
-----------------
All 3 possible reference voltage sources are supported:
- Internal reference
- External 1.2V reference and internal buffer
- External reference
The source is determined by the device tree. If ``ref-supply`` is present, then
the external reference is used. If ``refin-supply`` is present, then the internal
buffer is used. If neither is present, then the internal reference is used.
Unimplemented features
----------------------
- ``BUSY`` indication
- ``TURBO`` mode
- Daisy chain mode
Device attributes
=================
There are two types of ADCs in this family, pseudo-differential and fully
differential. The channel name is different depending on the type of ADC.
Pseudo-differential ADCs
------------------------
AD7944 and AD7985 are pseudo-differential ADCs and have the following attributes:
+---------------------------------------+--------------------------------------------------------------+
| Attribute | Description |
+=======================================+==============================================================+
| ``in_voltage0_raw`` | Raw ADC voltage value (*IN+* referenced to ground sense). |
+---------------------------------------+--------------------------------------------------------------+
| ``in_voltage0_scale`` | Scale factor to convert raw value to mV. |
+---------------------------------------+--------------------------------------------------------------+
Fully-differential ADCs
-----------------------
AD7986 is a fully-differential ADC and has the following attributes:
+---------------------------------------+--------------------------------------------------------------+
| Attribute | Description |
+=======================================+==============================================================+
| ``in_voltage0-voltage1_raw`` | Raw ADC voltage value (*IN+* - *IN-*). |
+---------------------------------------+--------------------------------------------------------------+
| ``in_voltage0-voltage1_scale`` | Scale factor to convert raw value to mV. |
+---------------------------------------+--------------------------------------------------------------+
Device buffers
==============
This driver supports IIO triggered buffers.
See :doc:`iio_devbuf` for more information.

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Documentation/iio/index.rst
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@ -16,6 +16,7 @@ Industrial I/O Kernel Drivers
.. toctree::
:maxdepth: 1
ad7944
adis16475
bno055
ep93xx_adc

1
MAINTAINERS
View File

@ -448,6 +448,7 @@ R: David Lechner <dlechner@baylibre.com>
S: Supported
W: https://ez.analog.com/linux-software-drivers
F: Documentation/devicetree/bindings/iio/adc/adi,ad7944.yaml
F: Documentation/iio/ad7944.rst
F: drivers/iio/adc/ad7944.c
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