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Date:   Thu, 23 Feb 2017 07:38:44 +0100
From:   Mariusz Bialonczyk <>
To:, Evgeniy Polyakov <>,
        Greg Kroah-Hartman <>
Cc:     Mariusz Bialonczyk <>
Subject: [PATCH v2 3/4] w1: add documentation for w1_ds2438

Signed-off-by: Mariusz Bialonczyk <>
 Documentation/w1/slaves/00-INDEX  |  2 ++
 Documentation/w1/slaves/w1_ds2438 | 63 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 65 insertions(+)
 create mode 100644 Documentation/w1/slaves/w1_ds2438

diff --git a/Documentation/w1/slaves/00-INDEX b/Documentation/w1/slaves/00-INDEX
index cbcca1d3a680..8d76718e1ea2 100644
--- a/Documentation/w1/slaves/00-INDEX
+++ b/Documentation/w1/slaves/00-INDEX
@@ -6,5 +6,7 @@ w1_ds2413
 	- The Maxim/Dallas Semiconductor ds2413 dual channel addressable switch.
 	- The Maxim/Dallas Semiconductor ds2423 counter device.
+	- The Maxim/Dallas Semiconductor ds2438 smart battery monitor.
 	- The Maxim/Dallas Semiconductor ds28e04 eeprom.
diff --git a/Documentation/w1/slaves/w1_ds2438 b/Documentation/w1/slaves/w1_ds2438
new file mode 100644
index 000000000000..b99f3674c5b4
--- /dev/null
+++ b/Documentation/w1/slaves/w1_ds2438
@@ -0,0 +1,63 @@
+Kernel driver w1_ds2438
+Supported chips:
+  * Maxim DS2438 Smart Battery Monitor
+supported family codes:
+        W1_FAMILY_DS2438        0x26
+Author: Mariusz Bialonczyk <>
+The DS2438 chip provides several functions that are desirable to carry in
+a battery pack. It also has a 40 bytes of nonvolatile EEPROM.
+Because the ability of temperature, current and voltage measurement, the chip
+is also often used in weather stations and applications such as: rain gauge,
+wind speed/direction measuring, humidity sensing, etc.
+Current support is provided through the following sysfs files (all files
+except "iad" are readonly):
+This file controls the 'Current A/D Control Bit' (IAD) in the
+Status/Configuration Register.
+Writing a zero value will clear the IAD bit and disables the current
+Writing value "1" is setting the IAD bit (enables the measurements).
+The IAD bit is enabled by default in the DS2438.
+When writing to sysfs file bits 2-7 are ignored, so it's safe to write ASCII.
+An I/O error is returned when there is a problem setting the new value.
+This file provides full 8 bytes of the chip Page 0 (00h).
+This page contains the most frequently accessed information of the DS2438.
+Internally when this file is read, the additional CRC byte is also obtained
+from the slave device. If it is correct, the 8 bytes page data are passed
+to userspace, otherwise an I/O error is returned.
+Opening and reading this file initiates the CONVERT_T (temperature conversion)
+command of the chip, afterwards the temperature is read from the device
+registers and provided as an ASCII decimal value.
+Important: The returned value has to be divided by 256 to get a real
+temperature in degrees Celsius.
+"vad", "vdd"
+Opening and reading this file initiates the CONVERT_V (voltage conversion)
+command of the chip.
+Depending on a sysfs filename a different input for the A/D will be selected:
+vad: general purpose A/D input (VAD)
+vdd: battery input (VDD)
+After the voltage conversion the value is returned as decimal ASCII.
+Note: The value is in mV, so to get a volts the value has to be divided by 10.

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