[PATCH] I2C: documentation update 2/3

This patch adds missing documentation for system health monitoring chips.
I would like to thank all people, who helped me with this project.

Signed-off-by: Rudolf Marek <r.marek@sh.cvut.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 76 insertions, 0 deletions

diff --git a/Documentation/i2c/chips/lm83 b/Documentation/i2c/chips/lm83
new file mode 100644
index 000000000000..061d9ed8ff43
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+++ b/Documentation/i2c/chips/lm83
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+Kernel driver lm83
+==================
+
+Supported chips:
+  * National Semiconductor LM83
+    Prefix: 'lm83'
+    Addresses scanned: I2C 0x18 - 0x1a, 0x29 - 0x2b, 0x4c - 0x4e
+    Datasheet: Publicly available at the National Semiconductor website
+               http://www.national.com/pf/LM/LM83.html
+
+
+Author: Jean Delvare <khali@linux-fr.org>
+
+Description
+-----------
+
+The LM83 is a digital temperature sensor. It senses its own temperature as
+well as the temperature of up to three external diodes. It is compatible
+with many other devices such as the LM84 and all other ADM1021 clones.
+The main difference between the LM83 and the LM84 in that the later can
+only sense the temperature of one external diode.
+
+Using the adm1021 driver for a LM83 should work, but only two temperatures
+will be reported instead of four.
+
+The LM83 is only found on a handful of motherboards. Both a confirmed
+list and an unconfirmed list follow. If you can confirm or infirm the
+fact that any of these motherboards do actually have an LM83, please
+contact us. Note that the LM90 can easily be misdetected as a LM83.
+
+Confirmed motherboards:
+    SBS         P014
+
+Unconfirmed motherboards:
+    Gigabyte    GA-8IK1100
+    Iwill       MPX2
+    Soltek      SL-75DRV5
+
+The driver has been successfully tested by Magnus Forsström, who I'd
+like to thank here. More testers will be of course welcome.
+
+The fact that the LM83 is only scarcely used can be easily explained.
+Most motherboards come with more than just temperature sensors for
+health monitoring. They also have voltage and fan rotation speed
+sensors. This means that temperature-only chips are usually used as
+secondary chips coupled with another chip such as an IT8705F or similar
+chip, which provides more features. Since systems usually need three
+temperature sensors (motherboard, processor, power supply) and primary
+chips provide some temperature sensors, the secondary chip, if needed,
+won't have to handle more than two temperatures. Thus, ADM1021 clones
+are sufficient, and there is no need for a four temperatures sensor
+chip such as the LM83. The only case where using an LM83 would make
+sense is on SMP systems, such as the above-mentioned Iwill MPX2,
+because you want an additional temperature sensor for each additional
+CPU.
+
+On the SBS P014, this is different, since the LM83 is the only hardware
+monitoring chipset. One temperature sensor is used for the motherboard
+(actually measuring the LM83's own temperature), one is used for the
+CPU. The two other sensors must be used to measure the temperature of
+two other points of the motherboard. We suspect these points to be the
+north and south bridges, but this couldn't be confirmed.
+
+All temperature values are given in degrees Celsius. Local temperature
+is given within a range of 0 to +85 degrees. Remote temperatures are
+given within a range of 0 to +125 degrees. Resolution is 1.0 degree,
+accuracy is guaranteed to 3.0 degrees (see the datasheet for more
+details).
+
+Each sensor has its own high limit, but the critical limit is common to
+all four sensors. There is no hysteresis mechanism as found on most
+recent temperature sensors.
+
+The lm83 driver will not update its values more frequently than every
+other second; reading them more often will do no harm, but will return
+'old' values.