[BUG] ideapad_acpi: fan_mode values 1/2/4 all trigger dust cleaning mode on IdeaPad 3 15ALC6 Ub

[BUG] ideapad_acpi: fan_mode values 1/2/4 all trigger dust cleaning mode on IdeaPad 3 15ALC6 Ub

[Sourajyoti Basak]

Hi everyone,

I am forwarding a bug I initially opened on Bugzilla (Bug 221353)
regarding the ideapad_acpi fan_mode behavior on the Lenovo IdeaPad 3
15ALC6 Ub.

Note: This is the exact same hardware I recently reported regarding the
EC thermal throttling limits.

## DMI

- system-manufacturer: LENOVO
- system-version: IdeaPad 3 15ALC6 Ub
- system-product-name: 82KU
- bios-version: GLCN46WW

## Kernel

Linux ideapad 7.0.8-1-cachyos #1 SMP PREEMPT_DYNAMIC Fri, 15 May 2026
18:31:42 +0000 x86_64 GNU/Linux


# Description

According to Documentation/ABI/testing/sysfs-platform-ideapad-laptop

fan_mode supports:
0 = Super Silent
1 = Standard
2 = Dust Cleaning
4 = Efficient Thermal Dissipation

However, on this device:
- Writing 1, 2, or 4 all produce identical behavior.
- Fan enters a pulsing high-speed mode where it ramps up to max speed
and then ramps down to 0 RPM about 10 times. Consistent with "dust
cleaning" mode.
- Only value 0 behaves differently. It changes it to the default/"Super
Silent" mode.

Here is the observation table:
| Input | Transition (immediately afterwards)   | Finish (after 1 min) |
|-------|---------------------------------------|----------------------|
| 0     | immediately 133, minimal fan activity | 133                  |

| 1     | 3, enters "dust cleaning" mode        | 5                    |

| 2     | 3                                     | 5                    |

| 4     | 3                                     | 5                    |


# Steps to Reproduce

1. Switch to a fan mode.
- echo 0 | sudo tee
/sys/bus/platform/drivers/ideapad_acpi/VPC2004:00/fan_mode
- echo 1 | sudo tee
/sys/bus/platform/drivers/ideapad_acpi/VPC2004:00/fan_mode
- echo 2 | sudo tee
/sys/bus/platform/drivers/ideapad_acpi/VPC2004:00/fan_mode
- echo 4 | sudo tee
/sys/bus/platform/drivers/ideapad_acpi/VPC2004:00/fan_mode

2. Observe that all of them except mode "0" (a.k.a. "Super Silent" mode)
make the fan enter the "dust cleaning" mode.


# Expected

Different fan behaviors per documented modes.


# Actual

All non-zero modes behave like dust cleaning.


Best Regards,
Sourajyoti Basak