linux-kernel - no hwmon entries in sysfs for thermal on raspberry pi 1b

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Date:   Fri, 8 Dec 2017 20:53:10 +0100
From:   Alexander Dahl <post@...pocky.de>
To:     linux-kernel@...r.kernel.org
Cc:     Jean Delvare <jdelvare@...e.com>,
        Guenter Roeck <linux@...ck-us.net>,
        linux-hwmon@...r.kernel.org, linux-pm@...r.kernel.org
Subject: no hwmon entries in sysfs for thermal on raspberry pi 1b

Hei hei,

I have v4.15-rc2 vanilla running on the original Raspberry Pi 1B aka
bcm2835 (not rev2, not the 1B+ or plus), compiled with ptxdist /
DistroKit, using bcm2835-rpi-b.dts from arch/arm/boot/dts as device
tree file. I try to get temperature values from the SoC with
lm-sensors (for using it in some other project). After reading an
issue report on the lm-sensors github project [1] I checked my kernel
config. The following is set:

    CONFIG_HWMON=y
    CONFIG_THERMAL_HWMON=y
    CONFIG_THERMAL=y
    CONFIG_THERMAL_OF=y
    CONFIG_BCM2835_THERMAL=y

There's one thermal zone in sysfs and I get some temperature which I
suppose is the temp of the SoC in m°C:

    root@...troKit:~ cat /sys/class/thermal/thermal_zone0/temp 
    42236

However, there's nothing below /sys/class/hwmon and I'm wondering why.
There's a thermal zone named 'cpu-thermal' defined and active in DT.

I tried to read some driver code and as far as I understood
thermal_add_hwmon_sysfs() must be called somewhere to get entries for
hwmon in sysfs, and this is done in thermal_zone_device_register(), so
probably a thermal zone must be present somehow, but it seems to be,
at least I can read temp values from it.

What piece am I missing? Is it some kind of configuration I did wrong?

Greets
Alex

[1] https://github.com/groeck/lm-sensors/issues/30

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