Hello All,
Firstly I'd like to thank Guenter for all his work adding support for the
nct6776f superIO chip.
During my testing of the driver on a Asus p8p67 pro motherboard and a Arctic
cooling fan I've come across a small problem that the RPM reading is
sometimes incorrect, usually the incorrect reading is almost double the
expected value and is only incorrect for 2 seconds (Next actual read from
the chip). Looking at the tacho signal from the fan with an oscilloscope I
can see short pulses/dropouts which cause the incorrect reading. Looking
through the data sheet I see that the nct6776f and nct6775f both support
de-bouncing the fan rpm signal (logical device b address 0xf0 bit 1-5 for
nct6776f or 1-4 for nct6775f). After enabling the rpm de-bounce for the CPU
fan I've not seen any more miss readings. I tested for 24hours and usually I
see a incorrect reading within 10-30 minutes.
The first question is, should we offer the possibility to enable rpm
de-bounce for chips that support it? If yes then what interface should we
use? I can see 3 possibilities:-
1) Through sysfs fanX_debounce (0/1). I already have a patch for this and
the diff is about 60 lines of code
2) Through a module parameter (fan_debounce=X) where X could be 0/1 for
disable/enable for all fans or a decimal value which is the bit pattern for
the de-bounce to enable.
3) Always enable the fan de-bounce if the chip supports it.
Note enabling de-bounce does not appear to have any negative effects.
Regards
Ian Dobson
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