On Sat, Mar 8, 2014 at 11:50 PM, Guenter Roeck <linux@xxxxxxxxxxxx> 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. > > You might also need the 10 uF capacitor on the FB pin. Hmm, interesting, but then I wonder how it works fine when getting the data from userspace with ioctl (i.e .without the driver) through /dev/i2c-1. There must be some trick in that case that I am not yet aware of. I will double check the schematics on Monday. Thanks! _______________________________________________ lm-sensors mailing list lm-sensors@xxxxxxxxxxxxxx http://lists.lm-sensors.org/mailman/listinfo/lm-sensors
