On 03/08/2014 10:36 PM, Laszlo Papp wrote:
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.
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@desktop:~$ 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
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