lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  PHC 
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date:	Sun, 9 Mar 2014 06:36:53 +0000
From:	Laszlo Papp <>
To:	Guenter Roeck <>
Cc:	LKML <>,
Subject: Re: [lm-sensors] Tachometer speed returned rather than absolute fan speed?

On Sat, Mar 8, 2014 at 11:50 PM, 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 <> 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.

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
More majordomo info at
Please read the FAQ at

Powered by blists - more mailing lists