Add a section to the ad7944 documentation describing how to use the
driver with SPI offloading.
Signed-off-by: David Lechner <dlechner@baylibre.com>
---
v5 changes: new patch in v5
---
Documentation/iio/ad7944.rst | 24 +++++++++++++++++++++++-
1 file changed, 23 insertions(+), 1 deletion(-)
diff --git a/Documentation/iio/ad7944.rst b/Documentation/iio/ad7944.rst
index 0d26e56aba88..e6dbe4d7f58c 100644
--- a/Documentation/iio/ad7944.rst
+++ b/Documentation/iio/ad7944.rst
@@ -46,6 +46,8 @@ CS mode, 3-wire, without busy indicator
To select this mode in the device tree, set the ``adi,spi-mode`` property to
``"single"`` and omit the ``cnv-gpios`` property.
+This is the only wiring configuration supported when using `SPI offload support`_.
+
CS mode, 4-wire, without busy indicator
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -106,7 +108,6 @@ Unimplemented features
----------------------
- ``BUSY`` indication
-- ``TURBO`` mode
Device attributes
@@ -147,6 +148,27 @@ AD7986 is a fully-differential ADC and has the following attributes:
In "chain" mode, additional chips will appear as additional voltage input
channels, e.g. ``in_voltage2-voltage3_raw``.
+SPI offload support
+===================
+
+To be able to achieve the maximum sample rate, the driver can be used with the
+`AXI SPI Engine`_ to provide SPI offload support.
+
+.. _AXI SPI Engine: http://analogdevicesinc.github.io/hdl/projects/pulsar_adc/index.html
+
+When SPI offload is being used, some attributes will be different.
+
+* ``trigger`` directory is removed.
+* ``in_voltage0_sampling_frequency`` attribute is added for setting the sample
+ rate.
+* ``in_voltage0_sampling_frequency_available`` attribute is added for querying
+ the max sample rate.
+* ``timestamp`` channel is removed.
+* Buffer data format may be different compared to when offload is not used,
+ e.g. the ``in_voltage0_type`` attribute.
+
+If the ``turbo-gpios`` property is present in the device tree, the driver will
+turn on TURBO during buffered reads and turn it off otherwise.
Device buffers
==============
--
2.43.0