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docs: iio: ad7944: add documentation for chain mode 

Add documentation for chain mode support that was recently added to the
AD7944 ADC driver.

Signed-off-by: David Lechner <dlechner@baylibre.com>
Link: https://lore.kernel.org/r/20240425-iio-ad7944-chain-mode-v1-2-9d9220ff21e1@baylibre.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
This commit is contained in:
David Lechner 2024-04-25 09:10:00 -05:00 committed by Jonathan Cameron
parent 64ce7d4348
commit 633e3015ca
1 changed files with 28 additions and 2 deletions
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30
Documentation/iio/ad7944.rst
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@ -24,7 +24,7 @@ Supported features
SPI wiring modes
----------------
The driver currently supports two of the many possible SPI wiring configurations.
The driver currently supports three of the many possible SPI wiring configurations.
CS mode, 3-wire, without busy indicator
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@ -68,6 +68,27 @@ CS mode, 4-wire, without busy indicator
To select this mode in the device tree, omit the ``adi,spi-mode`` property and
provide the ``cnv-gpios`` property.
Chain mode, without busy indicator
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
.. code-block::
+-------------+
+-------------------------+--------------------| CS |
v v | |
+--------------------+ +--------------------+ | HOST |
| CNV | | CNV | | |
+--->| SDI AD7944 SDO |--->| SDI AD7944 SDO |-------->| SDI |
| | SCK | | SCK | | |
GND +--------------------+ +--------------------+ | |
^ ^ | |
+-------------------------+--------------------| SCLK |
+-------------+
To select this mode in the device tree, set the ``adi,spi-mode`` property to
``"chain"``, add the ``spi-cs-high`` flag, add the ``#daisy-chained-devices``
property, and omit the ``cnv-gpios`` property.
Reference voltage
-----------------
@ -86,7 +107,6 @@ Unimplemented features
- ``BUSY`` indication
- ``TURBO`` mode
- Daisy chain mode
Device attributes
@ -108,6 +128,9 @@ AD7944 and AD7985 are pseudo-differential ADCs and have the following attributes
| ``in_voltage0_scale`` | Scale factor to convert raw value to mV. |
+---------------------------------------+--------------------------------------------------------------+
In "chain" mode, additional chips will appear as additional voltage input
channels, e.g. ``in_voltage1_raw``.
Fully-differential ADCs
-----------------------
@ -121,6 +144,9 @@ AD7986 is a fully-differential ADC and has the following attributes:
| ``in_voltage0-voltage1_scale`` | Scale factor to convert raw value to mV. |
+---------------------------------------+--------------------------------------------------------------+
In "chain" mode, additional chips will appear as additional voltage input
channels, e.g. ``in_voltage2-voltage3_raw``.
Device buffers
==============