xref: /openbmc/linux/Documentation/misc-devices/ad525x_dpot.rst (revision 4b4193256c8d3bc3a5397b5cd9494c2ad386317d)

.. SPDX-License-Identifier: GPL-2.0

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AD525x Digital Potentiometers
=============================

The ad525x_dpot driver exports a simple sysfs interface.  This allows you to
work with the immediate resistance settings as well as update the saved startup
settings.  Access to the factory programmed tolerance is also provided, but
interpretation of this settings is required by the end application according to
the specific part in use.

Files
=====

Each dpot device will have a set of eeprom, rdac, and tolerance files.  How
many depends on the actual part you have, as will the range of allowed values.

The eeprom files are used to program the startup value of the device.

The rdac files are used to program the immediate value of the device.

The tolerance files are the read-only factory programmed tolerance settings
and may vary greatly on a part-by-part basis.  For exact interpretation of
this field, please consult the datasheet for your part.  This is presented
as a hex file for easier parsing.

Example
=======

Locate the device in your sysfs tree.  This is probably easiest by going into
the common i2c directory and locating the device by the i2c slave address::

	# ls /sys/bus/i2c/devices/
	0-0022  0-0027  0-002f

So assuming the device in question is on the first i2c bus and has the slave
address of 0x2f, we descend (unrelated sysfs entries have been trimmed)::

	# ls /sys/bus/i2c/devices/0-002f/
	eeprom0 rdac0 tolerance0

You can use simple reads/writes to access these files::

	# cd /sys/bus/i2c/devices/0-002f/

	# cat eeprom0
	0
	# echo 10 > eeprom0
	# cat eeprom0
	10

	# cat rdac0
	5
	# echo 3 > rdac0
	# cat rdac0
	3