668. Controlling the fan speed of an Nvidia card when you're using the nouveau driver and no xorg.conf

 My old GT210 has served me well, but I've had a few odd freezes recently, coupled with weird graphics behaviour. It's a pity, since it's a nice, silent fan-less graphics card from way back when: https://www.gigabyte.com/Graphics-Card/GV-N210SL-1GI#ov

Although some of it may be due to switching back and forth between VGA and HDMI output (between an old HP 19'' and my new fancy xp pen display) I ripped it out and replaced it with an almost as ancient GT 520 (https://www.gigabyte.com/Graphics-Card/GV-N520OC-1GI#ov)

The fan isn't loud, but it's there, and it's distracting since I'm working in a home environment (Corona!).

Looking online I found these posts:
http://floppym.blogspot.com/2013/07/fan-control-with-nouveau.html
https://forums.opensuse.org/showthread.php/501517-OS-13-1-Driver-quot-nouveau-quot-Unable-to-command-fan-speed-Nvidia-6800-GS
https://www.kernel.org/doc/Documentation/thermal/nouveau_thermal

So, first to check if fan control is possible:

me@indium:~$ find /sys -name pwm1_enable
find: ‘/sys/kernel/debug’: Permission denied
/sys/devices/platform/it87.2624/hwmon/hwmon2/pwm1_enable
/sys/devices/platform/it87.2656/hwmon/hwmon3/pwm1_enable
/sys/devices/pci0000:00/0000:00:03.0/0000:05:00.0/hwmon/hwmon0/pwm1_enable
me@indium:~$ readlink /sys/devices/pci0000:00/0000:00:03.0/0000:05:00.0/driver
../../../../bus/pci/drivers/nouveau

Good, and we got the hwmon number -- 0. 

I then created a script called gpufan.sh:

sudo sh -c "echo 1 > /sys/class/hwmon/hwmon0/pwm1_enable"
sudo sh -c "echo 35 > /sys/class/hwmon/hwmon0/pwm1_min"
sudo sh -c "echo 45 > /sys/class/hwmon/hwmon0/pwm1"

I set the min% to 35 -- it used to be 65. And I tested my way to 45% as a good compromise between noise and temperature. By default the fan speed was >4,000 rpm. Output from sensors now:

nouveau-pci-0500
Adapter: PCI adapter
GPU core:     +0.90 V  (min =  +0.90 V, max =  +1.11 V)
fan1:        2790 RPM
temp1:        +34.0°C  (high = +95.0°C, hyst =  +3.0°C)
                       (crit = +105.0°C, hyst =  +5.0°C)
                       (emerg = +135.0°C, hyst =  +5.0°C)