[PATCH v3 3/3] docs: iio: add documentation for adxl380 driver

[Antoniu Miclaus <antoniu.miclaus@analog.com>]

Add documentation for adxl380 driver which describes the driver
device files and shows how the user may use the ABI for various
scenarios (configuration, measurement, etc.).

Signed-off-by: Ramona Gradinariu <ramona.gradinariu@analog.com>
Signed-off-by: Antoniu Miclaus <antoniu.miclaus@analog.com>
---
changes in v3:
 - performed docs build via `make htmldocs` and no warnings were
   detected for adxl380 documentation. 
 Documentation/iio/adxl380.rst | 238 ++++++++++++++++++++++++++++++++++
 Documentation/iio/index.rst   |   1 +
 2 files changed, 239 insertions(+)
 create mode 100644 Documentation/iio/adxl380.rst

diff --git a/Documentation/iio/adxl380.rst b/Documentation/iio/adxl380.rst
new file mode 100644
index 000000000000..a64e330a18ee
--- /dev/null
+++ b/Documentation/iio/adxl380.rst
@@ -0,0 +1,238 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+===============
+ADXL380 driver
+===============
+
+This driver supports Analog Device's ADXL380/382 on SPI/I2C bus.
+
+1. Supported devices
+====================
+
+* `ADXL380 <https://www.analog.com/ADXL380>`_
+* `ADXL382 <https://www.analog.com/ADXL382>`_
+
+The ADXL380/ADXL382 is a low noise density, low power, 3-axis accelerometer with
+selectable measurement ranges. The ADXL380 supports the ±4 g, ±8 g, and ±16 g
+ranges, and the ADXL382 supports ±15 g, ±30 g, and ±60 g ranges.
+
+The ADXL380/ADXL382 offers industry leading noise, enabling precision
+applications with minimal calibration. The low noise, and low power
+ADXL380/ADXL382 enables accurate measurement in an environment with high
+vibration, heart sounds and audio.
+
+2. Device attributes
+====================
+
+Accelerometer measurements are always provided.
+
+Temperature data are also provided. This data can be used to monitor the
+internal system temperature or to improve the temperature stability of the
+device via calibration.
+
+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, depending on the characteristics and features of the hardware
+device in questions. These files are consistently generalized and documented in
+the IIO ABI documentation.
+
+The following tables show the adxl380 related device files, found in the
+specific device folder path ``/sys/bus/iio/devices/iio:deviceX``.
+
++---------------------------------------------------+----------------------------------------------------------+
+| 3-Axis Accelerometer related device files         | Description                                              |
++---------------------------------------------------+----------------------------------------------------------+
+| in_accel_scale                                    | Scale for the accelerometer channels.                    |
++---------------------------------------------------+----------------------------------------------------------+
+| in_accel_filter_high_pass_3db_frequency           | Low pass filter bandwidth.                               |
++---------------------------------------------------+----------------------------------------------------------+
+| in_accel_filter_high_pass_3db_frequency_available | Available low pass filter bandwidth configurations.      |
++---------------------------------------------------+----------------------------------------------------------+
+| in_accel_filter_low_pass_3db_frequency            | High pass filter bandwidth.                              |
++---------------------------------------------------+----------------------------------------------------------+
+| in_accel_filter_low_pass_3db_frequency_available  | Available high pass filter bandwidth configurations.     |
++---------------------------------------------------+----------------------------------------------------------+
+| in_accel_x_calibbias                              | Calibration offset for the X-axis accelerometer channel. |
++---------------------------------------------------+----------------------------------------------------------+
+| in_accel_x_raw                                    | Raw X-axis accelerometer channel value.                  |
++---------------------------------------------------+----------------------------------------------------------+
+| in_accel_y_calibbias                              | y-axis acceleration offset correction                    |
++---------------------------------------------------+----------------------------------------------------------+
+| in_accel_y_raw                                    | Raw Y-axis accelerometer channel value.                  |
++---------------------------------------------------+----------------------------------------------------------+
+| in_accel_z_calibbias                              | Calibration offset for the Z-axis accelerometer channel. |
++---------------------------------------------------+----------------------------------------------------------+
+| in_accel_z_raw                                    | Raw Z-axis accelerometer channel value.                  |
++---------------------------------------------------+----------------------------------------------------------+
+
++----------------------------------+--------------------------------------------+
+| Temperature sensor related files | Description                                |
++----------------------------------+--------------------------------------------+
+| in_temp_raw                      | Raw temperature channel value.             |
++----------------------------------+--------------------------------------------+
+| in_temp_offset                   | Offset for the temperature sensor channel. |
++----------------------------------+--------------------------------------------+
+| in_temp_scale                    | Scale for the temperature sensor channel.  |
++----------------------------------+--------------------------------------------+
+
++------------------------------+----------------------------------------------+
+| Miscellaneous device files   | Description                                  |
++------------------------------+----------------------------------------------+
+| name                         | Name of the IIO device.                      |
++------------------------------+----------------------------------------------+
+| sampling_frequency           | Currently selected sample rate.              |
++------------------------------+----------------------------------------------+
+| sampling_frequency_available | Available sampling frequency configurations. |
++------------------------------+----------------------------------------------+
+
+Channels processed values
+-------------------------
+
+A channel value can be read from its _raw attribute. The value returned is the
+raw value as reported by the devices. To get the processed value of the channel,
+apply the following formula:
+
+.. code-block:: bash
+
+        processed value = (_raw + _offset) * _scale
+
+Where _offset and _scale are device attributes. If no _offset attribute is
+present, simply assume its value is 0.
+
+The adis16475 driver offers data for 2 types of channels, the table below shows
+the measurement units for the processed value, which are defined by the IIO
+framework:
+
++-------------------------------------+---------------------------+
+| Channel type                        | Measurement unit          |
++-------------------------------------+---------------------------+
+| Acceleration on X, Y, and Z axis    | Meters per Second squared |
++-------------------------------------+---------------------------+
+| Temperature                         | Millidegrees Celsius      |
++-------------------------------------+---------------------------+
+
+Usage examples
+--------------
+
+Show device name:
+
+.. code-block:: bash
+
+	root:/sys/bus/iio/devices/iio:device0> cat name
+        adxl382
+
+Show accelerometer channels value:
+
+.. code-block:: bash
+
+        root:/sys/bus/iio/devices/iio:device0> cat in_accel_x_raw
+        -1771
+        root:/sys/bus/iio/devices/iio:device0> cat in_accel_y_raw
+        282
+        root:/sys/bus/iio/devices/iio:device0> cat in_accel_z_raw
+        -1523
+        root:/sys/bus/iio/devices/iio:device0> cat in_accel_scale
+        0.004903325
+
+- X-axis acceleration = in_accel_x_raw * in_accel_scale = −8.683788575 m/s^2
+- Y-axis acceleration = in_accel_y_raw * in_accel_scale = 1.38273765 m/s^2
+- Z-axis acceleration = in_accel_z_raw * in_accel_scale = -7.467763975 m/s^2
+
+Set calibration offset for accelerometer channels:
+
+.. code-block:: bash
+
+        root:/sys/bus/iio/devices/iio:device0> cat in_accel_x_calibbias
+        0
+
+        root:/sys/bus/iio/devices/iio:device0> echo 50 > in_accel_x_calibbias
+        root:/sys/bus/iio/devices/iio:device0> cat in_accel_x_calibbias
+        50
+
+Set sampling frequency:
+
+.. code-block:: bash
+
+	root:/sys/bus/iio/devices/iio:device0> cat sampling_frequency
+        16000
+        root:/sys/bus/iio/devices/iio:device0> cat sampling_frequency_available
+        16000 32000 64000
+
+        root:/sys/bus/iio/devices/iio:device0> echo 32000 > sampling_frequency
+        root:/sys/bus/iio/devices/iio:device0> cat sampling_frequency
+        32000
+
+Set low pass filter bandwidth for accelerometer channels:
+
+.. code-block:: bash
+
+        root:/sys/bus/iio/devices/iio:device0> cat in_accel_filter_low_pass_3db_frequency
+        32000
+        root:/sys/bus/iio/devices/iio:device0> cat in_accel_filter_low_pass_3db_frequency_available
+        32000 8000 4000 2000
+
+        root:/sys/bus/iio/devices/iio:device0> echo 2000 > in_accel_filter_low_pass_3db_frequency
+        root:/sys/bus/iio/devices/iio:device0> cat in_accel_filter_low_pass_3db_frequency
+        2000
+
+3. Device buffers
+=================
+
+This driver supports IIO buffers.
+
+All devices support retrieving the raw acceleration and temperature measurements
+using buffers.
+
+Usage examples
+--------------
+
+Select channels for buffer read:
+
+.. code-block:: bash
+
+        root:/sys/bus/iio/devices/iio:device0> echo 1 > scan_elements/in_accel_x_en
+        root:/sys/bus/iio/devices/iio:device0> echo 1 > scan_elements/in_accel_y_en
+        root:/sys/bus/iio/devices/iio:device0> echo 1 > scan_elements/in_accel_z_en
+        root:/sys/bus/iio/devices/iio:device0> echo 1 > scan_elements/in_temp_en
+
+Set the number of samples to be stored in the buffer:
+
+.. code-block:: bash
+
+        root:/sys/bus/iio/devices/iio:device0> echo 10 > buffer/length
+
+Enable buffer readings:
+
+.. code-block:: bash
+
+        root:/sys/bus/iio/devices/iio:device0> echo 1 > buffer/enable
+
+Obtain buffered data:
+
+.. code-block:: bash
+
+        root:/sys/bus/iio/devices/iio:device0> hexdump -C /dev/iio\:device0
+        ...
+        002bc300  f7 e7 00 a8 fb c5 24 80  f7 e7 01 04 fb d6 24 80  |......$.......$.|
+        002bc310  f7 f9 00 ab fb dc 24 80  f7 c3 00 b8 fb e2 24 80  |......$.......$.|
+        002bc320  f7 fb 00 bb fb d1 24 80  f7 b1 00 5f fb d1 24 80  |......$...._..$.|
+        002bc330  f7 c4 00 c6 fb a6 24 80  f7 a6 00 68 fb f1 24 80  |......$....h..$.|
+        002bc340  f7 b8 00 a3 fb e7 24 80  f7 9a 00 b1 fb af 24 80  |......$.......$.|
+        002bc350  f7 b1 00 67 fb ee 24 80  f7 96 00 be fb 92 24 80  |...g..$.......$.|
+        002bc360  f7 ab 00 7a fc 1b 24 80  f7 b6 00 ae fb 76 24 80  |...z..$......v$.|
+        002bc370  f7 ce 00 a3 fc 02 24 80  f7 c0 00 be fb 8b 24 80  |......$.......$.|
+        002bc380  f7 c3 00 93 fb d0 24 80  f7 ce 00 d8 fb c8 24 80  |......$.......$.|
+        002bc390  f7 bd 00 c0 fb 82 24 80  f8 00 00 e8 fb db 24 80  |......$.......$.|
+        002bc3a0  f7 d8 00 d3 fb b4 24 80  f8 0b 00 e5 fb c3 24 80  |......$.......$.|
+        002bc3b0  f7 eb 00 c8 fb 92 24 80  f7 e7 00 ea fb cb 24 80  |......$.......$.|
+        002bc3c0  f7 fd 00 cb fb 94 24 80  f7 e3 00 f2 fb b8 24 80  |......$.......$.|
+        ...
+
+See ``Documentation/iio/iio_devbuf.rst`` for more information about how buffered
+data is structured.
+
+4. IIO Interfacing Tools
+========================
+
+See ``Documentation/iio/iio_tools.rst`` for the description of the available IIO
+interfacing tools.
diff --git a/Documentation/iio/index.rst b/Documentation/iio/index.rst
index 4c13bfa2865c..1ce5b24d40aa 100644
--- a/Documentation/iio/index.rst
+++ b/Documentation/iio/index.rst
@@ -20,5 +20,6 @@ Industrial I/O Kernel Drivers
    ad7944
    adis16475
    adis16480
+   adxl380
    bno055
    ep93xx_adc
-- 
2.45.2