linux-kernel - [PATCH v5 13/16] doc: iio: ad7944: describe offload support

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Message-Id: <20241115-dlech-mainline-spi-engine-offload-2-v5-13-bea815bd5ea5@baylibre.com>
Date: Fri, 15 Nov 2024 14:18:52 -0600
From: David Lechner <dlechner@...libre.com>
To: Mark Brown <broonie@...nel.org>, Jonathan Cameron <jic23@...nel.org>, 
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, 
 Conor Dooley <conor+dt@...nel.org>, 
 Nuno Sá <nuno.sa@...log.com>
Cc: Uwe Kleine-König <ukleinek@...nel.org>, 
 Michael Hennerich <Michael.Hennerich@...log.com>, 
 Lars-Peter Clausen <lars@...afoo.de>, David Jander <david@...tonic.nl>, 
 Martin Sperl <kernel@...tin.sperl.org>, linux-spi@...r.kernel.org, 
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, 
 linux-iio@...r.kernel.org, linux-pwm@...r.kernel.org, 
 David Lechner <dlechner@...libre.com>
Subject: [PATCH v5 13/16] doc: iio: ad7944: describe offload support

Add a section to the ad7944 documentation describing how to use the
driver with SPI offloading.

Signed-off-by: David Lechner <dlechner@...libre.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