docs: iio: convert to ReST

Rename the iio documentation files to ReST, add an
index for them and adjust in order to produce a nice html
output via the Sphinx build system.

At its new index.rst, let's add a :orphan: while this is not linked to
the main index.rst file, in order to avoid build warnings.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

1 files changed, 101 insertions, 0 deletions

diff --git a/Documentation/iio/iio_configfs.rst b/Documentation/iio/iio_configfs.rst
new file mode 100644
index 000000000000..ecbfdb3afef7
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+++ b/Documentation/iio/iio_configfs.rst
@@ -0,0 +1,101 @@
+===============================
+Industrial IIO configfs support
+===============================
+
+1. Overview
+===========
+
+Configfs is a filesystem-based manager of kernel objects. IIO uses some
+objects that could be easily configured using configfs (e.g.: devices,
+triggers).
+
+See Documentation/filesystems/configfs/configfs.txt for more information
+about how configfs works.
+
+2. Usage
+========
+
+In order to use configfs support in IIO we need to select it at compile
+time via CONFIG_IIO_CONFIGFS config option.
+
+Then, mount the configfs filesystem (usually under /config directory)::
+
+  $ mkdir /config
+  $ mount -t configfs none /config
+
+At this point, all default IIO groups will be created and can be accessed
+under /config/iio. Next chapters will describe available IIO configuration
+objects.
+
+3. Software triggers
+====================
+
+One of the IIO default configfs groups is the "triggers" group. It is
+automagically accessible when the configfs is mounted and can be found
+under /config/iio/triggers.
+
+IIO software triggers implementation offers support for creating multiple
+trigger types. A new trigger type is usually implemented as a separate
+kernel module following the interface in include/linux/iio/sw_trigger.h::
+
+  /*
+   * drivers/iio/trigger/iio-trig-sample.c
+   * sample kernel module implementing a new trigger type
+   */
+  #include <linux/iio/sw_trigger.h>
+
+
+  static struct iio_sw_trigger *iio_trig_sample_probe(const char *name)
+  {
+	/*
+	 * This allocates and registers an IIO trigger plus other
+	 * trigger type specific initialization.
+	 */
+  }
+
+  static int iio_trig_hrtimer_remove(struct iio_sw_trigger *swt)
+  {
+	/*
+	 * This undoes the actions in iio_trig_sample_probe
+	 */
+  }
+
+  static const struct iio_sw_trigger_ops iio_trig_sample_ops = {
+	.probe		= iio_trig_sample_probe,
+	.remove		= iio_trig_sample_remove,
+  };
+
+  static struct iio_sw_trigger_type iio_trig_sample = {
+	.name = "trig-sample",
+	.owner = THIS_MODULE,
+	.ops = &iio_trig_sample_ops,
+  };
+
+module_iio_sw_trigger_driver(iio_trig_sample);
+
+Each trigger type has its own directory under /config/iio/triggers. Loading
+iio-trig-sample module will create 'trig-sample' trigger type directory
+/config/iio/triggers/trig-sample.
+
+We support the following interrupt sources (trigger types):
+
+	* hrtimer, uses high resolution timers as interrupt source
+
+3.1 Hrtimer triggers creation and destruction
+---------------------------------------------
+
+Loading iio-trig-hrtimer module will register hrtimer trigger types allowing
+users to create hrtimer triggers under /config/iio/triggers/hrtimer.
+
+e.g::
+
+  $ mkdir /config/iio/triggers/hrtimer/instance1
+  $ rmdir /config/iio/triggers/hrtimer/instance1
+
+Each trigger can have one or more attributes specific to the trigger type.
+
+3.2 "hrtimer" trigger types attributes
+--------------------------------------
+
+"hrtimer" trigger type doesn't have any configurable attribute from /config dir.
+It does introduce the sampling_frequency attribute to trigger directory.