Re: [REGRESSION?] sensors and fancontrol not seeing armada_thermal on 3.12-rc series

[Guenter Roeck <linux@roeck-us.net>]

On 10/20/2013 11:10 AM, Arnaud Ebalard wrote:
> Hi,
>
> With 3.12-rc series, sysfs support for thermal susbsytem (and/or hwmon
> one) was modified in such a way that sensors utility (current 3.3.4
> version with 3.3.4 version of libsensors from lm-sensors package on
> Debian unstable) does not see the temperature sensor anymore on armada
> 370 platforms (not tested on others). Additionally, the changes break
> existing configurations of fancontrol utility, which prevents the
> fan to be regulated correctly w/o recreating an /etc/fancontrol w/
> pwmconfig.
>
> Here is what I have on my Armada 370-based system on a 3.11.5:
>
> # sensors
> g762-i2c-0-3e
> Adapter: mv64xxx_i2c adapter
> fan1:        2457 RPM  (div = 1)
>
> armada_thermal-virtual-0
> Adapter: Virtual device
> temp1:        +45.7°C
>
> And what I get on 3.12-rc6:
>
> # sensors
> g762-i2c-0-3e
> Adapter: mv64xxx_i2c adapter
> fan1:        1350 RPM  (div = 1)
>
>
> Monitoring what sensors does w/ strace, I started looking at the changes
> to /sys/class/hwmon/hwmon1/:
>
> On 3.11.5:
>
> # find /sys/class/hwmon/hwmon1/
> /sys/class/hwmon/hwmon1/
> /sys/class/hwmon/hwmon1/name
> /sys/class/hwmon/hwmon1/subsystem
> /sys/class/hwmon/hwmon1/uevent
> /sys/class/hwmon/hwmon1/temp1_input
>
> On 3.12-rc6:
>
> # find /sys/class/hwmon/hwmon1/
> /sys/class/hwmon/hwmon1/
> /sys/class/hwmon/hwmon1/name
> /sys/class/hwmon/hwmon1/device
> /sys/class/hwmon/hwmon1/subsystem
> /sys/class/hwmon/hwmon1/uevent
> /sys/class/hwmon/hwmon1/temp1_input
>
> # find /sys/class/hwmon/hwmon1/device/
> /sys/class/hwmon/hwmon1/device/
> /sys/class/hwmon/hwmon1/device/temp
> /sys/class/hwmon/hwmon1/device/type
> /sys/class/hwmon/hwmon1/device/hwmon1
> /sys/class/hwmon/hwmon1/device/hwmon1/name
> /sys/class/hwmon/hwmon1/device/hwmon1/device
> /sys/class/hwmon/hwmon1/device/hwmon1/subsystem
> /sys/class/hwmon/hwmon1/device/hwmon1/uevent
> /sys/class/hwmon/hwmon1/device/hwmon1/temp1_input
> /sys/class/hwmon/hwmon1/device/subsystem
> /sys/class/hwmon/hwmon1/device/policy
> /sys/class/hwmon/hwmon1/device/uevent
> /sys/class/hwmon/hwmon1/device/passive
>
> Is that expected? As for sensors, it *seems* to be bothered to find a
> device/ folder in /sys/class/hwmon/hwmon1/ w/o no name entry in it.
>

The 'name' attribute should not be the problem, since there is a 'name'
attribute in the /sys/class/hwmon/hwmon1/ directory.

Key difference is that there is now a 'device' subdirectory, which results
in different handling by libsensors; the entry is no longer a virtual entry
but is expected to have a real device attached to it. For this device,
libsensors tries to scan the 'subsystem' entry which in turn must be well
defined and known. My suspicion is that the reported subsystem may not be
recognized by libsensors.

One question is why there is now a device entry, even though this is still as
virtual as it was before. You'll have to ask the thermal subsystem maintainers
for an answer.

I am also concerned about the 'hwmon1' subdirectory underneath hwmon1/device;
that suggests that hwmon1 may be declared to be a child of itself, which would
obviously not be a good idea.

Also, note that the thermal subsystem creates (or may create) sensor attributes
after registering the hwmon device, which means you can not rely on the udev
event that comes with the hwmon device creation and assume that all sensor
attributes exist at that time. I don't currently know how to handle this situation.
This is not unique, though; the coretemp driver does the same. Just something
to keep in mind.

Guenter