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The ideapad-laptop.c file now exists inside drivers/platform/x86/lenovo/ directory. Updating the GitHub link to the correct path. Signed-off-by: Ninad Naik <ninadnaik07@gmail.com> Link: https://lore.kernel.org/r/20260417191411.713958-1-ninadnaik07@gmail.com Signed-off-by: Guenter Roeck <linux@roeck-us.net>
139 lines
6.1 KiB
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139 lines
6.1 KiB
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.. SPDX-License-Identifier: GPL-2.0-only
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===============================================================================================
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Kernel driver yogafan
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===============================================================================================
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Supported chips:
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* Lenovo Yoga, Legion, IdeaPad, Slim, Flex, and LOQ Embedded Controllers
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* Prefix: 'yogafan'
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* Addresses: ACPI handle (See Database Below)
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Author: Sergio Melas <sergiomelas@gmail.com>
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Description
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-----------
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This driver provides fan speed monitoring for modern Lenovo consumer laptops.
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Most Lenovo laptops do not provide fan tachometer data through standard
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ISA/LPC hardware monitoring chips. Instead, the data is stored in the
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Embedded Controller (EC) and exposed via ACPI.
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The driver implements a **Rate-Limited Lag (RLLag)** filter to handle
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the low-resolution and jittery sampling found in Lenovo EC firmware.
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Hardware Identification and Multiplier Logic
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--------------------------------------------
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The driver supports two distinct EC architectures. Differentiation is handled
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deterministically via a DMI Product Family quirk table during the probe phase,
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eliminating the need for runtime heuristics.
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1. 8-bit EC Architecture (Multiplier: 100)
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- **Families:** Yoga, IdeaPad, Slim, Flex.
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- **Technical Detail:** These models allocate a single 8-bit register for
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tachometer data. Since 8-bit fields are limited to a value of 255, the
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BIOS stores fan speed in units of 100 RPM (e.g., 42 = 4200 RPM).
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2. 16-bit EC Architecture (Multiplier: 1)
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- **Families:** Legion, LOQ.
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- **Technical Detail:** High-performance gaming models require greater
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precision for fans exceeding 6000 RPM. These use a 16-bit word (2 bytes)
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storing the raw RPM value directly.
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Filter Details
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--------------
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The RLLag filter is a passive discrete-time first-order lag model that ensures:
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- **Smoothing:** Low-resolution step increments are smoothed into 1-RPM increments.
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- **Slew-Rate Limiting:** Prevents unrealistic readings by capping the change
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to 1500 RPM/s, matching physical fan inertia.
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- **Polling Independence:** The filter math scales based on the time delta
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between userspace reads, ensuring a consistent physical curve regardless
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of polling frequency.
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Suspend and Resume
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------------------
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The driver utilizes the boottime clock (ktime_get_boottime()) to calculate the
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sampling delta. This ensures that time spent in system suspend is accounted
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for. If the delta exceeds 5 seconds (e.g., after waking the laptop), the
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filter automatically resets to the current hardware value to prevent
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reporting "ghost" RPM data from before the sleep state.
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Usage
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-----
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The driver exposes standard hwmon sysfs attributes:
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=============== ============================
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Attribute Description
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fanX_input Filtered fan speed in RPM.
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=============== ============================
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Note: If the hardware reports 0 RPM, the filter is bypassed and 0 is reported
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immediately to ensure the user knows the fan has stopped.
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====================================================================================================
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LENOVO FAN CONTROLLER: MASTER REFERENCE DATABASE (2026)
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====================================================================================================
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::
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MODEL (DMI PN) | FAMILY / SERIES | EC OFFSET | FULL ACPI OBJECT PATH | WIDTH | MULTiplier
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----------------------------------------------------------------------------------------------------
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82N7 | Yoga 14cACN | 0x06 | \_SB.PCI0.LPC0.EC0.FANS | 8-bit | 100
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80V2 / 81C3 | Yoga 710/720 | 0x06 | \_SB.PCI0.LPC0.EC0.FAN0 | 8-bit | 100
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83E2 / 83DN | Yoga Pro 7/9 | 0xFE | \_SB.PCI0.LPC0.EC0.FANS | 8-bit | 100
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82A2 / 82A3 | Yoga Slim 7 | 0x06 | \_SB.PCI0.LPC0.EC0.FANS | 8-bit | 100
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81YM / 82FG | IdeaPad 5 | 0x06 | \_SB.PCI0.LPC0.EC0.FAN0 | 8-bit | 100
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82JW / 82JU | Legion 5 (AMD) | 0xFE/0xFF | \_SB.PCI0.LPC0.EC0.FANS (Fan1) | 16-bit | 1
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82JW / 82JU | Legion 5 (AMD) | 0xFE/0xFF | \_SB.PCI0.LPC0.EC0.FA2S (Fan2) | 16-bit | 1
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82WQ | Legion 7i (Int) | 0xFE/0xFF | \_SB.PCI0.LPC0.EC0.FANS (Fan1) | 16-bit | 1
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82WQ | Legion 7i (Int) | 0xFE/0xFF | \_SB.PCI0.LPC0.EC0.FA2S (Fan2) | 16-bit | 1
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82XV / 83DV | LOQ 15/16 | 0xFE/0xFF | \_SB.PCI0.LPC0.EC0.FANS /FA2S | 16-bit | 1
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83AK | ThinkBook G6 | 0x06 | \_SB.PCI0.LPC0.EC0.FAN0 | 8-bit | 100
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81X1 | Flex 5 | 0x06 | \_SB.PCI0.LPC0.EC0.FAN0 | 8-bit | 100
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*Legacy* | Pre-2020 Models | 0x06 | \_SB.PCI0.LPC.EC.FAN0 | 8-bit | 100
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----------------------------------------------------------------------------------------------------
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METHODOLOGY & IDENTIFICATION:
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1. DSDT ANALYSIS (THE PATH):
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BIOS ACPI tables were analyzed using 'iasl' and cross-referenced with
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public dumps. Internal labels (FANS, FAN0, FA2S) are mapped to
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EmbeddedControl OperationRegion offsets.
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2. EC MEMORY MAPPING (THE OFFSET):
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Validated by matching NBFC (NoteBook FanControl) XML logic with DSDT Field
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definitions found in BIOS firmware.
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3. DATA-WIDTH ANALYSIS (THE MULTIPLIER):
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- 8-bit (Multiplier 100): Standard for Yoga/IdeaPad. Raw values (0-255).
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- 16-bit (Multiplier 1): Standard for Legion/LOQ. Two registers (0xFE/0xFF).
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References
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----------
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1. **ACPI Specification (Field Objects):** Documentation on how 8-bit vs 16-bit
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fields are accessed in OperationRegions.
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https://uefi.org/specs/ACPI/6.5/05_ACPI_Software_Programming_Model.html#field-objects
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2. **NBFC Projects:** Community-driven reverse engineering
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of Lenovo Legion/LOQ EC memory maps (16-bit raw registers).
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https://github.com/hirschmann/nbfc/tree/master/Configs
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3. **Linux Kernel Timekeeping API:** Documentation for ktime_get_boottime() and
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handling deltas across suspend states.
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https://www.kernel.org/doc/html/latest/core-api/timekeeping.html
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4. **Lenovo IdeaPad Laptop Driver:** Reference for DMI-based hardware
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feature gating in Lenovo laptops.
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https://github.com/torvalds/linux/blob/master/drivers/platform/x86/lenovo/ideapad-laptop.c
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