I haven an older nvidia card:

-->
# hwinfo --gfxcard
23: PCI 100.0: 0300 VGA compatible controller (VGA)             
  [Created at pci.378]
  Unique ID: VCu0.x9HhAPKYST4
  Parent ID: vSkL.sBCJa6uSmM6
  SysFS ID: /devices/pci0000:00/0000:00:01.0/0000:01:00.0
  SysFS BusID: 0000:01:00.0
  Hardware Class: graphics card
  Model: "nVidia Quadro FX 1500"
  Vendor: pci 0x10de "nVidia Corporation"
  Device: pci 0x029e "Quadro FX 1500"
  SubVendor: pci 0x10de "nVidia Corporation"
  SubDevice: pci 0x032c 
  Revision: 0xa1
  Driver: "nouveau"
  Driver Modules: "drm"
  Memory Range: 0xf2000000-0xf2ffffff (rw,non-prefetchable)
  Memory Range: 0xe0000000-0xefffffff (ro,non-prefetchable)
  Memory Range: 0xf1000000-0xf1ffffff (rw,non-prefetchable)
  I/O Ports: 0x4000-0x4fff (rw)
  IRQ: 28 (8673 events)
  I/O Ports: 0x3c0-0x3df (rw)
  Module Alias: "pci:v000010DEd0000029Esv000010DEsd0000032Cbc03sc00i00"
  Driver Info #0:
    XFree86 v4 Server Module: nv
  Config Status: cfg=new, avail=yes, need=no, active=unknown
  Attached to: #8 (PCI bridge)

Primary display adapter: #23
--<

This worked fine with the nouveau driver until Leap42.3.
With Leap15 now, the graphics card fan starts running at maximum speed and
never stops.
The switch to maximum speed might be in context with temperature management.
I get the following messages:

-->
2018-08-01T07:16:01.878010+02:00 alpha kernel: [  379.049048] nouveau
0000:01:00.0: therm: temperature (90 C) hit the 'fanboost' threshold
2018-08-01T07:16:08.881928+02:00 alpha kernel: [  386.049548] nouveau
0000:01:00.0: therm: temperature (87 C) went below the 'fanboost' threshold
--<

I would expect that the fan speed decreases after the temperature goes below
the fanboost threshold, but it doesn't.
As written above, on 42.3, the fan stays nice quiet at low rotation speed:

-->
# cat /sys/class/drm/card0/device/hwmon/hwmon0/pwm1
20
--<

Attaching the sysfs valume of noveau hwmon from 42.3 and 15.
Any hint what I need to tune to get the 42.3 behaviour back?