Bug report: HP: WMI: Fan speed reading and PWM control fails + dmesg related errors

[Julien ROBIN <julien.robin28@free.fr>]

Hello there,

Using intended WMI drivers and associated sysfs through `pwm1_enable` 
and `pwm1` virtual files generally allows manual setting of fan speed on 
laptops, which can be useful to set maximum speed when running rude CPU 
and GPU tasks for example (to avoid reaching crazy temperatures).

I have a new machine (HP 16-s1034nf) on which (even with latest mainline 
kernel 6.13-rc2) this pwm fan control sysfs interface is failing, and 
fan speed reported values are stuck to zero (even when they are 
blowing), through hp-wpi driver.

Just to be sure, I checked using "HP Omen Gaming Hub" application in 
Windows that the hardware is actually capable of fan speed reading and 
setting (the answer is yes).

In details:
  - `/sys/devices/platform/hp-wmi/hwmon/hwmon6/pwm1_enable` writing 
isn't applied (when writing "0", value is kept to "2" and writing "1" 
says write error: Invalid argument)
  - `/sys/devices/platform/hp-wmi/hwmon/hwmon6/pwm1` is missing
  - `/sys/devices/platform/hp-wmi/hwmon/hwmon6/fan1_input` is always 
stuck to 0 (even when fans are running)
  - `/sys/devices/platform/hp-wmi/hwmon/hwmon6/fan2_input` is always 
stuck to 0 too (this computer actually has 2 fans)

The interesting part of the dmesg output is the following:
	[...]
	input: HP WMI hotkeys as /devices/virtual/input/input15
	ACPI BIOS Error (bug): Could not resolve symbol [\_SB.PEP.DETY], 
AE_NOT_FOUND (20240322/psargs-332)
	ACPI Error: Aborting method \_SB.WMID.GTPS due to previous error 
(AE_NOT_FOUND) (20240322/psparse-529)
	ACPI Error: Aborting method \_SB.WMID.RDCF due to previous error 
(AE_NOT_FOUND) (20240322/psparse-529)
	ACPI Error: Aborting method \_SB.WMID.WHCM due to previous error 
(AE_NOT_FOUND) (20240322/psparse-529)
	ACPI Error: Aborting method \_SB.WMID.WMAA due to previous error 
(AE_NOT_FOUND) (20240322/psparse-529)
	[...]

All of the previous dmesg messages are disappearing when booting with 
`module_blacklist=hp_wmi` into the Kernel command line. In place of 
them, we got a single line:
	[..]
	Module hp_wmi is blacklisted
	[..]

So I understand these errors mentioning ACPI are caused by what the 
hp_wmi driver is doing (or trying to).

In order to be sure this isn't an ACPI Firmware bug from the laptop's 
ACPI tables, I used Firmware Test Suite on "DSDT" as explained into 
https://wiki.ubuntu.com/Kernel/Reference/WMI
It turns out imperfections found by FWTS aren't related to the HP WMI 
interfaces GUID. Anyway I'm still providing all of the related files and 
results in case someone needs them.

Unfortunately, going further alone is a little bit outside of my skills, 
but I keep available for any questions and tests.
As it's my first bug report into this mailing list, I hope I didn't make 
too much mistakes! Sincerely sorry in advance if I did.

Best regards,
Julien ROBIN

Notes:
  - Using Debian 13/Trixie (testing)
  - Problem still exists on latest 6.13-rc2 "pure" kernel with no DKMS 
loaded driver

I placed all of the required files (dmidecode, dmesg, kernel config, and 
ACPI tables related stuff) into the following link:
  - 
https://pix-server-sorel.luoss.fr/Manual/Linux/HP-WMI/Bug-Report-2024-12-12/