Kernel driver lm75

Supported chips:

Author: Frodo Looijaard <>


The LM75 implements one temperature sensor. Limits can be set through the Overtemperature Shutdown register and Hysteresis register. Each value can be set and read to half-degree accuracy. An alarm is issued (usually to a connected LM78) when the temperature gets higher then the Overtemperature Shutdown value; it stays on until the temperature falls below the Hysteresis value. All temperatures are in degrees Celsius, and are guaranteed within a range of -55 to +125 degrees.

The driver caches the values for a period varying between 1 second for the slowest chips and 125 ms for the fastest chips; reading it more often will do no harm, but will return ‘old’ values.

The original LM75 was typically used in combination with LM78-like chips on PC motherboards, to measure the temperature of the processor(s). Clones are now used in various embedded designs.

The LM75 is essentially an industry standard; there may be other LM75 clones not listed here, with or without various enhancements, that are supported. The clones are not detected by the driver, unless they reproduce the exact register tricks of the original LM75, and must therefore be instantiated explicitly. Higher resolution up to 16-bit is supported by this driver, other specific enhancements are not.

The LM77 is not supported, contrary to what we pretended for a long time. Both chips are simply not compatible, value encoding differs.