linux/Documentation/iio/iio_configfs.rst
Gwendal Grignou dafcf4ed83 iio: hrtimer: Allow sub Hz granularity
Allow setting frequency below 1Hz or sub 1Hz precision.
Useful for slow sensors like ALS.

Test frequency is set properly:
modprobe iio-trig-hrtimer && \
mkdir /sys/kernel/config/iio/triggers/hrtimer/t1 && \
cd /sys/bus/iio/devices/triggerX ;
for i in 1 .1 .01 .001 ; do
  echo $i > sampling_frequency
  cat sampling_frequency
done

Signed-off-by: Gwendal Grignou <gwendal@chromium.org>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20210226014733.2108544-1-gwendal@chromium.org
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
2021-03-25 19:13:49 +00:00

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===============================
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.rst 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_sample_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.
That attribute sets the polling frequency in Hz, with mHz precision.