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linux
iio: Documentation: Add IIO configfs documentation
Signed-off-by: Daniel Baluta <daniel.baluta@intel.com>
Acked-by: Crt Mori <cmo@melexis.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
authored by
Daniel Baluta
and committed by
Jonathan Cameron
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ac5006a2
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Documentation/ABI/testing/configfs-iio
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Documentation/ABI/testing/configfs-iio
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What: /config/iio
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Date: October 2015
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KernelVersion: 4.4
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Contact: linux-iio@vger.kernel.org
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Description:
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This represents Industrial IO configuration entry point
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directory. It contains sub-groups corresponding to IIO
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objects.
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What: /config/iio/triggers
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Date: October 2015
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KernelVersion: 4.4
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Description:
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Industrial IO software triggers directory.
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What: /config/iio/triggers/hrtimers
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Date: October 2015
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KernelVersion: 4.4
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Description:
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High resolution timers directory. Creating a directory here
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will result in creating a hrtimer trigger in the IIO subsystem.
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Documentation/iio/iio_configfs.txt
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Documentation/iio/iio_configfs.txt
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Industrial IIO configfs support
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1. Overview
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Configfs is a filesystem-based manager of kernel objects. IIO uses some
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objects that could be easily configured using configfs (e.g.: devices,
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triggers).
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See Documentation/filesystems/configfs/configfs.txt for more information
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about how configfs works.
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2. Usage
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In order to use configfs support in IIO we need to select it at compile
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time via CONFIG_IIO_CONFIGFS config option.
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Then, mount the configfs filesystem (usually under /config directory):
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$ mkdir /config
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$ mount -t configfs none /config
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At this point, all default IIO groups will be created and can be accessed
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under /config/iio. Next chapters will describe available IIO configuration
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objects.
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3. Software triggers
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One of the IIO default configfs groups is the "triggers" group. It is
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automagically accessible when the configfs is mounted and can be found
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under /config/iio/triggers.
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IIO software triggers implementation offers support for creating multiple
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trigger types. A new trigger type is usually implemented as a separate
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kernel module following the interface in include/linux/iio/sw_trigger.h:
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/*
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* drivers/iio/trigger/iio-trig-sample.c
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* sample kernel module implementing a new trigger type
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*/
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#include <linux/iio/sw_trigger.h>
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static struct iio_sw_trigger *iio_trig_sample_probe(const char *name)
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{
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/*
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* This allocates and registers an IIO trigger plus other
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* trigger type specific initialization.
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*/
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}
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static int iio_trig_hrtimer_remove(struct iio_sw_trigger *swt)
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{
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/*
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* This undoes the actions in iio_trig_sample_probe
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*/
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}
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static const struct iio_sw_trigger_ops iio_trig_sample_ops = {
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.probe = iio_trig_sample_probe,
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.remove = iio_trig_sample_remove,
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};
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static struct iio_sw_trigger_type iio_trig_sample = {
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.name = "trig-sample",
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.owner = THIS_MODULE,
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.ops = &iio_trig_sample_ops,
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};
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module_iio_sw_trigger_driver(iio_trig_sample);
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Each trigger type has its own directory under /config/iio/triggers. Loading
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iio-trig-sample module will create 'trig-sample' trigger type directory
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/config/iio/triggers/trig-sample.
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We support the following interrupt sources (trigger types):
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* hrtimer, uses high resolution timers as interrupt source
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3.1 Hrtimer triggers creation and destruction
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Loading iio-trig-hrtimer module will register hrtimer trigger types allowing
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users to create hrtimer triggers under /config/iio/triggers/hrtimer.
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e.g:
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$ mkdir /config/triggers/hrtimer/instance1
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$ rmdir /config/triggers/hrtimer/instance1
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Each trigger can have one or more attributes specific to the trigger type.
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3.2 "hrtimer" trigger types attributes
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"hrtimer" trigger type doesn't have any configurable attribute from /config dir.
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It does introduce the sampling_frequency attribute to trigger directory.