Hi Ben, On Thu, 29 Apr 2010 15:21:46 +1000, Benjamin Herrenschmidt wrote: > I'm writing some support for d-link dns323 rev C1 NAS. It has a fan that > is controlled by some non-programmable PWM circuit. Basically, all I can > do is tweak to GPIOs that controls the feed into the circuitry for the > fans to be off, slow or fast. > > I don't know what the actual PWM values are for "slow" or "fast". I > -might- be able to do some measurements but I can't promise it. > > Now I'm trying to do a simple hwmon driver for that in order to easy > userspace support for these guys, and I don't really see a 'nice' way to > expose that which would fit the interfaces documented > Documentation/hwmon/sysfs-interface. > > So before I do something horrible, I felt I might poke you guys see if > you have a good idea here :-) > > Before I read the above document I was thinking about a sysfs file that > contains "off", "slow" or "fast" but it looks like this won't fit at all > the typical hwmon APIs. Indeed, that wouldn't fit. The nearest entry in the document is: pwm[1-*] Pulse width modulation fan control. Integer value in the range 0 to 255 RW 255 is max or 100%. In your case, the file would have only 3 possible values, with "off" mapping to 0, and "slow" and "fast" mapping to arbitrary positive values, like 64 and 192 or whatever you think is suitable. I understand that in your case, you don't really control the PWM output directly, but we do not have any interface for this, and I don't think there would be much value in adding one. That being said, I am also only mildly convinced that fitting your chip in the standard pwm1 interface will be very helpful. I don't really expect tools such as the fancontrol script to behave properly when the pwm1 file only support a small number of discrete values. So the benefit of using the standard file name and semantics seems thin. > Another comment while at it is when implementing the thermal control for > PowerMacs a while back (windfarm etc...) I had to deal with two > different type of interfaces to fans. RPM controlled and PWM controlled. > > The later basically let me program a percentile value (a percent of the > duty cycle). This is exactly what pwm[1-*] files are about, except that we used range 0-255 instead of 0-100 for historical and practical reasons. > I looks like the described sysfs interface only does RPM, or at least > doesn't provide a way to expose the units used... For RPM-controlled, look at the following entry instead: fan[1-*]_target Desired fan speed Unit: revolution/min (RPM) RW Only makes sense if the chip supports closed-loop fan speed control based on the measured fan speed. One significant difference is that, in this case, you always know which fan you control, while in the pwm[1-*] case you don't. -- Jean Delvare _______________________________________________ lm-sensors mailing list lm-sensors@xxxxxxxxxxxxxx http://lists.lm-sensors.org/mailman/listinfo/lm-sensors
