[PATCH v2 6/6] docs: iio: ad4030: add documentation

Esteban Blanc
2024-12-19T16:11:25Z

This adds a new page to document how to use the ad4030 ADC driver

Signed-off-by: Esteban Blanc <eblanc@baylibre.com>
---
Documentation/iio/ad4030.rst | 181 +++++++++++++++++++++++++++++++++++++++++++
Documentation/iio/index.rst | 1 +
MAINTAINERS | 1 +
3 files changed, 183 insertions(+)

diff --git a/Documentation/iio/ad4030.rst b/Documentation/iio/ad4030.rst
new file mode 100644
index 0000000000000000000000000000000000000000..41ce5ca5c710c46a0995d1b127fa1c10fca4c1eb
--- /dev/null
+++ b/Documentation/iio/ad4030.rst
@@ -0,0 +1,181 @@
+.. SPDX-License-Identifier: GPL-2.0-only
+
+=============
+AD4030 driver
+=============
+
+ADC driver for Analog Devices Inc. AD4030 and similar devices. The module name
+is ``ad4030``.
+
+
+Supported devices
+=================
+
+The following chips are supported by this driver:
+
+* `AD4030-24 <https://www.analog.com/AD4030-24>`_
+* `AD4032-24 <https://www.analog.com/AD4032-24>`_
+* `AD4630-16 <https://www.analog.com/AD4630-16>`_
+* `AD4630-24 <https://www.analog.com/AD4630-24>`_
+* `AD4632-16 <https://www.analog.com/AD4632-16>`_
+* `AD4632-24 <https://www.analog.com/AD4632-24>`_
+
+IIO channels
+============
+
+Each "hardware" channel as described in the datasheet is split in 2 IIO
+channels:
+
+- One channel for the differential data
+- One channel for the common byte.
+
+The possible IIO channels depending on the numbers of "hardware" channel are:
+
++------------------------------------+------------------------------------+
+| 1 channel ADC | 2 channels ADC |
++====================================+====================================+
+| - voltage0-voltage1 (differential) | - voltage0-voltage1 (differential) |
+| - voltage2 (common-mode) | - voltage2-voltage3 (differential) |
+| | - voltage4 (common-mode) |
+| | - voltage5 (common-mode) |
++------------------------------------+------------------------------------+
+
+Labels
+------
+
+For ease of use, the IIO channels provide a label. For a differential channel,
+the label is ``differentialN`` where ``N`` is the "hardware" channel id. For a
+common-mode channel, the label is ``common-modeN`` where ``N`` is the
+"hardware" channel id.
+
+The possible labels are:
+
++-----------------+-----------------+
+| 1 channel ADC | 2 channels ADC |
++=================+=================+
+| - differential0 | - differential0 |
+| - common-mode0 | - differential1 |
+| | - common-mode0 |
+| | - common-mode1 |
++-----------------+-----------------+
+
+Supported features
+==================
+
+SPI wiring modes
+----------------
+
+The driver currently supports the following SPI wiring configurations:
+
+One lane mode
+^^^^^^^^^^^^^
+
+In this mode, each channel has its own SDO line to send the conversion results.
+At the moment this mode can only be used on AD4030 which has one channel so only
+one SDO line is used.
+
+.. code-block::
+
+ +-------------+ +-------------+
+ | ADC | | HOST |
+ | | | |
+ | CNV |<--------| CNV |
+ | CS |<--------| CS |
+ | SDI |<--------| SDO |
+ | SDO0 |-------->| SDI |
+ | SCLK |<--------| SCLK |
+ +-------------+ +-------------+
+
+Interleaved mode
+^^^^^^^^^^^^^^^^
+
+In this mode, both channels conversion results are bit interleaved one SDO line.
+As such the wiring is the same as `One lane mode`_.
+
+SPI Clock mode
+--------------
+
+Only the SPI clocking mode is supported.
+
+Output modes
+------------
+
+There are more exposed IIO channels than channels as describe in the devices
+datasheet. This is due to the `Differential data + common-mode`_ encoding
+2 types of information in one conversion result. As such a "device" channel
+provides 2 IIO channels, one for the differential data and one for the common
+byte.
+
+Differential data
+^^^^^^^^^^^^^^^^^
+
+This mode is selected when:
+
+- Only differential channels are enabled in a buffered read
+- Oversampling attribute is set to 1
+
+Differential data + common-mode
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+This mode is selected when:
+
+- Differential and common-mode channels are enabled in a buffered read
+- Oversampling attribute is set to 1
+
+For the 24-bits chips, this mode is also available with 16-bits differential
+data but is not selectable yet.
+
+Averaged differential data
+^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+This mode is selected when:
+
+- Only differential channels are selected enabled in a buffered read
+- Oversampling attribute is greater than 1
+
+Digital Gain and Offset
+-----------------------
+
+Each differential data channel has a 16-bits unsigned configurable hardware
+gain applied to it. By default it's equal to 1. Note that applying gain can
+cause numerical saturation.
+
+Each differential data channel has a signed configurable hardware offset.
+For the ADCs ending in ``-24``, the gain is encoded on 24-bits.
+Likewise, the ADCs ending in ``-16`` have a gain encoded on 16-bits. Note that
+applying an offset can cause numerical saturation.
+
+The final differential data returned by the ADC is computed by first applying
+the gain, then the offset.
+
+The gain is controlled by the ``calibscale`` IIO attribute while the offset is
+controlled by the ``calibbias`` attribute.
+
+Reference voltage
+-----------------
+
+The chip supports an external reference voltage via the ``REF`` input or an
+internal buffered reference voltage via the ``REFIN`` input. The driver looks
+at the device tree to determine which is being used. If ``ref-supply`` is
+present, then the external reference voltage is used and the internal buffer is
+disabled. If ``refin-supply`` is present, then the internal buffered reference
+voltage is used.
+
+Reset
+-----
+
+Both hardware and software reset are supported. The driver looks first at the
+device tree to see if the ``reset-gpio`` is populated.
+If not present, the driver will fallback to a software reset by wiring to the
+device's registers.
+
+Unimplemented features
+----------------------
+
+- ``BUSY`` indication
+- Additional wiring modes
+- Additional clock modes
+- Differential data 16-bits + common-mode for 24-bits chips
+- Overrange events
+- Test patterns
+
diff --git a/Documentation/iio/index.rst b/Documentation/iio/index.rst
index 074dbbf7ba0a087ab117efaf3d69fc559fc00fa5..982ac1bd9dfd7bfd54bfbf87d6258e6249edf799 100644
--- a/Documentation/iio/index.rst
+++ b/Documentation/iio/index.rst
@@ -19,6 +19,7 @@ Industrial I/O Kernel Drivers
:maxdepth: 1

ad4000
+ ad4030
ad4695
ad7380
ad7606
diff --git a/MAINTAINERS b/MAINTAINERS
index 943c48fc0a75f475049758cf3791ba6d19748a63..775e7487de2309f7e7d89c9362bc4fa9a25d3095 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -1282,6 +1282,7 @@ L: linux-iio@vger.kernel.org
S: Supported
W: https://ez.analog.com/linux-software-drivers
F: Documentation/devicetree/bindings/iio/adc/adi,ad4030.yaml
+F: Documentation/iio/ad4030.rst
F: drivers/iio/adc/ad4030.c

ANALOG DEVICES INC AD4130 DRIVER

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2.47.0