On Sat 2014-03-08 15:50:49, Guenter Roeck wrote: > On 03/07/2014 10:17 AM, Guenter Roeck wrote: > >On Fri, Mar 07, 2014 at 03:47:08PM +0000, Laszlo Papp wrote: > >>On Fri, Mar 7, 2014 at 3:37 PM, Jean Delvare <jdelvare@xxxxxxx> wrote: > >>>>>I'm quite confused. While I admit that the term "tachometer speed" is > >>>>>awkward, the max6650 driver is reporting fan speeds in RPM as every > >>>>>other hwmon driver. So I really have no idea what you think is wrong. > >>>>>What did you think "tachometer speed" was, if not the fan speed? Does > >>>>>the max6650 driver not return correct fan speeds for you? > >> > >>That is some strange behavior. If I do "echo 1 > pwm1_enable; echo 0 > > >>pwm1; cat fan1_input", I still see 30 for the connected fan, whereas I > >>can see it stopped. Is this an expected behavior? I would expect zero > >>as a user. > >> > >I seem to recall that I had seen that as well, with no fan connected. > >Maybe the tachometer registers always read at least '1'. I would think > >it is wrong, but we'll have to understand the chip a bit better > >to be able to provide a fix. Unless you already have a fix ready, > >of course. I'll try to re-test tonight if I find the time. > > > > The reason is (most likely) that your fan input does not have a pull-up > resistor. Per datasheet, the fan inputs need a 10kOhm pull-up resistor. > I confirmed this with my test board - with the pull-up resistor, > inputs read 0, Without pull-up, the reported value is 1, which > translates to 30 RPM. While this is hardware problem, it might make sense for kernel to work around it -- return 0 in case 30 RPM observed. Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html _______________________________________________ lm-sensors mailing list lm-sensors@xxxxxxxxxxxxxx http://lists.lm-sensors.org/mailman/listinfo/lm-sensors
