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Message-ID: <531C2097.5020004@roeck-us.net> Date: Sun, 09 Mar 2014 00:04:39 -0800 From: Guenter Roeck <linux@...ck-us.net> To: Laszlo Papp <lpapp@....org> CC: LKML <linux-kernel@...r.kernel.org>, lm-sensors@...sensors.org Subject: Re: [lm-sensors] Tachometer speed returned rather than absolute fan speed? On 03/08/2014 10:36 PM, Laszlo Papp wrote: > On Sat, Mar 8, 2014 at 11:50 PM, Guenter Roeck <linux@...ck-us.net> 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@...e.de> 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. > With i2cdump on my system I can see that the tachometer register holds 0 if the resistor is in place, and the sensors command reports a fan speed or 0 rpm. If the resistor is not in place, the register content is 1 and sensors reports 30 rpm. sudo i2cdump -y -f 1 0x48 No size specified (using byte-data access) 0 1 2 3 4 5 6 7 8 9 a b c d e f 0123456789abcdef 00: 00 00 0a 0a ff ff 00 00 00 00 00 00 01 01 00 00 ..??........??.. 10: 01 01 01 01 1f 1f 02 02 91 91 91 91 91 91 91 91 ???????????????? 20: 00 00 0a 0a ff ff 00 00 00 00 00 00 01 01 00 00 ..??........??.. groeck@...ktop:~$ sensors max6651-i2c-1-48 max6651-i2c-1-48 Adapter: i2c-diolan-u2c at bus 003 device 002 fan1: 30 RPM (div = 4) fan2: 0 RPM fan3: 30 RPM fan4: 30 RPM Only fan2 (TACH1 chip input) has the resistor installed. Guenter -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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