Unable to set fan mode/Dell XPS 7390/dell_smm/pwm1_enable

[piyueh]

Describe the bug

fan2go fan init -i <fan> and fan2go gave errors complaining being unable to set fan mode through pwm*_enable.

To Reproduce

1. $ fan2go detect (I'm only posting relevant sections here):

   Click me to expand

   > dell_smm-isa-0000
     Fans     Index  Channel  Label        RPM  PWM  Auto 
     -----------------------------------------------------
              1      1        hwmon4/fan1  0    0    false
              2      2        hwmon4/fan2  0    0    false
     Sensors  Index  Label                       Value
     -------------------------------------------------
              1      hwmon4/temp1 (temp1_input)  44000
              2      hwmon4/temp2 (temp2_input)  37000
              3      hwmon4/temp3 (temp3_input)  38000
              4      hwmon4/temp4 (temp4_input)  32000
              5      hwmon4/temp5 (temp5_input)  38000
              6      hwmon4/temp6 (temp6_input)  38000
              7      hwmon4/temp7 (temp7_input)  37000
   
   > coretemp-isa-0000
     Sensors  Index  Label                       Value
     -------------------------------------------------
              1      Package id 0 (temp1_input)  53000
              2      Core 0 (temp2_input)        51000
              3      Core 1 (temp3_input)        51000
              4      Core 2 (temp4_input)        52000
              5      Core 3 (temp5_input)        50000
              6      Core 4 (temp6_input)        52000
              7      Core 5 (temp7_input)        48000

2. $ cat /etc/fan2go/fan2go.yaml:

   Click me to expand

   fans:
     - id: fan-1
       hwmon:
         platform: dell_smm-isa-0000
         rpmChannel: 1
         pwmChannel: 1
         index: 0
       neverStop: true
       curve: fan-curve-1
   sensors:
     - id: cpu-package
       hwmon:
         platform: coretemp-isa-0000
         index: 1
   curves:
     - id: fan-curve-1
       linear:
         sensor: cpu-package
         min: 50
         max: 90

3. # fan2go fan init -i fan-1, I got

   Click me to expand

   INFO  Using configuration file at: /etc/fan2go/fan2go.yaml
   INFO  Using persistence at: /etc/fan2go/fan2go.db
   INFO  Deleting existing data for fan 'fan-1'...
   INFO  Computing pwm map...
   ERROR   Unable to set Fan Mode of 'fan-1' to "1": PWM mode stuck to -1
   ERROR   Unable to set Fan Mode of 'fan-1' to "0": write
       /sys/devices/platform/dell_smm_hwmon/hwmon/hwmon5/pwm1_enable:
       invalid argument
   INFO  Measuring RPM curve...
   ERROR   Unable to set Fan Mode of 'fan-1' to "1": PWM mode stuck to -1
   ERROR   Unable to set Fan Mode of 'fan-1' to "0": write
       /sys/devices/platform/dell_smm_hwmon/hwmon/hwmon5/pwm1_enable:
       invalid argument
   WARNING  Could not enable manual fan mode on fan-1, trying to
       continue anyway...
   SUCCESS  Done!
   INFO  Using configuration file at: /etc/fan2go/fan2go.yaml
   fan-1
   ------------
   Min PWM    0
   Start PWM  0
   Max PWM    0

Expected behavior

No error messages.

Desktop (please complete the following information):

• Laptop model: Dell XPS 7390
• Distro: Arch Linux
• uname -a: 6.3.2-arch1-1
• sensors -v: sensors version 3.6.0+git with libsensors version 3.6.0+git
• fan2go version: commit c20619e

Additional context

According to hwmon's documentation, for dell_smm, the file pwm1_enable does not accept 0. A value of 1 to pwm1_enable means disabling the automatic BIOS fan control, while 2 means enabling such automatic control. See here.

[markusressel]

fan2go tries to set 1 first and only falls back to 0.
Since both seem to fail and the returned value seems to be -1 this might be a permission problem.

[piyueh]

You are right. I think simply using sudo does not give enough permission to write to pwm*_enable. On my machine, I have to actually be the root to write to the file.

[piyueh]

I'm re-opening this issue because maybe some other people may help. I'm unsure if this is simply a permission issue or something else. I found that writing 1 to the file pwm1_enable did not give any permission error. The permission error appeared when fan2go tried to read the value from pwm1_enable for confirmation. On my machine (Dell XPS13 7390 and Arch Linux), pwm1_enable is not readable even as a root (cat, tail, head, or even opening/reading it with Python/C code did not work). I haven't figured out why.

So I think the permission error message originated from line 163 when trying to read the value:

fan2go/internal/fans/hwmon.go

Lines 160 to 169 in 0a6ea59

	func (fan *HwMonFan) SetPwmEnabled(value ControlMode) (err error) {
	err = util.WriteIntToFile(int(value), fan.Config.HwMon.PwmEnablePath)
	if err == nil {
	currentValue, err := util.ReadIntFromFile(fan.Config.HwMon.PwmEnablePath)
	if err != nil || ControlMode(currentValue) != value {
	return fmt.Errorf("PWM mode stuck to %d", currentValue)
	}
	}
	return err
	}

[piyueh]

@markusressel Just to give an update. If my understanding is correct, for Dell fans that rely on the dell_smm_hwmon kernel module, pwm1_enable is write-only. Therefore reading the value from pwm1_enable always fails. And so the code snippet referenced in my previous comment always returns an error.

See: https://docs.kernel.org/hwmon/dell-smm-hwmon.html. In the table of available sysfs interfaces, pwm1_enable is shown to be write-only.

Kernel driver dell-smm-hwmon — The Linux Kernel documentation

[markusressel]

Hmm interesting 🤔 I am not sure if we can test for this somehow in code and ignore the validation logic in case the pwm_enable is write-only. However, even if not, we could add a config property to disable it manually.

As I am not able to test this with real hardware myself, we would need to test it on yours. I will let you know when I have something ready.