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authorMauro Carvalho Chehab <mchehab+huawei@kernel.org>2020-06-15 09:50:13 +0300
committerJonathan Corbet <corbet@lwn.net>2020-06-19 23:05:49 +0300
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tree821de190af69dd16eeed8ccc480864275f13af31 /Documentation/misc-devices/ad525x_dpot.rst
parent3471b9f7e43d3505fcffc63d0271f13dd9246873 (diff)
downloadlinux-8a05eb89cb84eba1091bdc6baa9d0e463655779f.tar.xz
docs: misc-devices/pci-endpoint-test.txt: convert to ReST
- use title markups; - mark literal blocks. Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org> Link: https://lore.kernel.org/r/1b1f4e5e57fd2065828cecc9d07afbd247349e94.1592203650.git.mchehab+huawei@kernel.org Signed-off-by: Jonathan Corbet <corbet@lwn.net>
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+.. SPDX-License-Identifier: GPL-2.0
+
+=============================
+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