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w1: add ability to set (SRAM) and store (EEPROM) configuration for temp sensors like DS18B20

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Since many temperature sensors come "preconfigured" with a lower
precision, people are stuck at that precision when running on a kernel
based device (unlike the Dallas 1Wire library for e.g. Arduino, which
supports writing the configuration/scratchpad). This patch adds write
support for the scratchpad/precision registers via w1_slave sysfs.

Signed-off-by: Ben Sen <[email protected]>
Acked-by: Evgeniy Polyakov <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
This commit is contained in:
Ben Sen 2016-05-01 23:23:33 +02:00 • committed by Greg Kroah-Hartman
commit 0a19f129d7
3 changed files with 222 additions and 8 deletions
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10
Documentation/w1/slaves/w1_therm
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@ -33,7 +33,15 @@ temperature conversion at a time. If none of the devices are parasite
powered it would be possible to convert all the devices at the same
time and then go back to read individual sensors. That isn't
currently supported. The driver also doesn't support reduced
precision (which would also reduce the conversion time).
precision (which would also reduce the conversion time) when reading values.
Writing a value between 9 and 12 to the sysfs w1_slave file will change the
precision of the sensor for the next readings. This value is in (volatile)
SRAM, so it is reset when the sensor gets power-cycled.
To store the current precision configuration into EEPROM, the value 0
has to be written to the sysfs w1_slave file. Since the EEPROM has a limited
amount of writes (>50k), this command should be used wisely.
The module parameter strong_pullup can be set to 0 to disable the
strong pullup, 1 to enable autodetection or 2 to force strong pullup.