lenovo-gentoo/Touchpad-Touchscreen-Setup.md

Touchpad and Touchscreen Setup

Date: 2025-11-05

Problem

Both touchpad and touchscreen were not functional despite being detected by the system.

Hardware Details

Touchpad

• Model: ELAN901C
• Type: I2C HID device
• ACPI Path: ELAN901C:00
• Modalias: acpi:ELAN901C:PNP0C50:
• I2C Bus: i2c-3 (AMDI0010:00)
• Sysfs Path: /sys/bus/i2c/devices/i2c-ELAN901C:00

Touchscreen

• Model: ELAN0678
• Type: I2C HID multitouch display
• ACPI Path: ELAN0678:00
• Modalias: acpi:ELAN0678:PNP0C50:
• I2C Bus: i2c-4 (AMDI0010:01)
• Sysfs Path: /sys/bus/i2c/devices/i2c-ELAN0678:00

Root Cause Analysis

The kernel was missing two critical configurations:

1. I2C HID ACPI binding support (CONFIG_I2C_HID_ACPI) - Required for ACPI-based I2C HID devices
2. AMD GPIO/Pinctrl support (CONFIG_PINCTRL_AMD) - Required for GPIO interrupts on AMD platforms

Original Kernel Configuration (First Issue)

CONFIG_I2C_HID=m
# CONFIG_I2C_HID_ACPI is not set  ← Problem #1!
# CONFIG_I2C_HID_OF is not set

Second Issue Discovered After First Reboot

# CONFIG_PINCTRL_AMD is not set  ← Problem #2!

Why both are needed:

• CONFIG_I2C_HID_ACPI: Allows the i2c-hid driver to bind to ACPI devices (PNP0C50)
• CONFIG_PINCTRL_AMD: Provides GPIO support for interrupt handling on AMD platforms

Without PINCTRL_AMD, the i2c-hid-acpi driver would hang when trying to configure device interrupts.

PNP0C50 Identifier

Both devices use PNP0C50, which is the ACPI HID (Hardware ID) for "HID over I2C" devices. This is a standard identifier for touchpads and touchscreens that communicate via I2C protocol using the HID standard.

Solution

Step 1: Enable I2C HID ACPI in Kernel Config

cd /usr/src/linux
sudo scripts/config --module I2C_HID_ACPI
# or: sudo sed -i 's/# CONFIG_I2C_HID_ACPI is not set/CONFIG_I2C_HID_ACPI=m/' .config

Step 2: Enable AMD Pinctrl Support

CRITICAL: This must be built-in (=y), not a module, because it provides GPIO interrupt support needed early in boot.

cd /usr/src/linux
sudo scripts/config --enable PINCTRL_AMD

Verification:

grep "CONFIG_I2C_HID_ACPI\|CONFIG_PINCTRL_AMD" .config
# Should output:
# CONFIG_I2C_HID_ACPI=m
# CONFIG_PINCTRL_AMD=y

Step 3: Rebuild Kernel

cd /usr/src/linux
sudo genkernel --makeopts=-j16 all

Build History:

• First rebuild: November 5, 2025 08:27 (added CONFIG_I2C_HID_ACPI)
• Second rebuild: November 5, 2025 09:44 (attempted PINCTRL_AMD)
• Final rebuild: November 5, 2025 ~10:00 (properly added CONFIG_PINCTRL_AMD=y)

Important Notes:

• Use --no-mrproper to preserve existing kernel config when doing incremental changes
• When enabling new options with dependencies, sometimes a full rebuild without --no-mrproper is needed
• --makeopts=-j16: Uses all 16 CPU threads for parallel compilation

Step 4: Verify Build

# Check i2c-hid modules
find /lib/modules/6.12.41-gentoo-x86_64/ -name "*i2c*hid*.ko*"

# Verify PINCTRL_AMD is built-in (not a module)
zcat /proc/config.gz | grep PINCTRL_AMD
# Should show: CONFIG_PINCTRL_AMD=y (after reboot with new kernel)

Expected modules:

/lib/modules/6.12.41-gentoo-x86_64/kernel/drivers/hid/i2c-hid/i2c-hid.ko
/lib/modules/6.12.41-gentoo-x86_64/kernel/drivers/hid/i2c-hid/i2c-hid-acpi.ko

Note: PINCTRL_AMD won't appear as a .ko file because it's built-in to the kernel.

Step 5: Create Kernel Backup

# Create timestamped backup of previous kernel
sudo cp /boot/vmlinuz-6.12.41-gentoo-x86_64.old /boot/vmlinuz-6.12.41-gentoo-x86_64.backup-20251105
sudo cp /boot/initramfs-6.12.41-gentoo-x86_64.img.old /boot/initramfs-6.12.41-gentoo-x86_64.img.backup-20251105
sudo cp /boot/System.map-6.12.41-gentoo-x86_64.old /boot/System.map-6.12.41-gentoo-x86_64.backup-20251105

Step 6: Reboot (Required)

The new kernel and modules are in place:

• /boot/vmlinuz-6.12.41-gentoo-x86_64 (Nov 5 ~10:00 - final build)
• /boot/initramfs-6.12.41-gentoo-x86_64.img (Nov 5 ~10:00)

No GRUB changes needed - GRUB already boots from these filenames.

Post-Reboot Verification

Check Module Loading

# Check if i2c-hid-acpi module is loaded
lsmod | grep i2c_hid

# Expected output:
# i2c_hid_acpi          16384  0
# i2c_hid               32768  1 i2c_hid_acpi

Check Input Devices

# List all input devices
cat /proc/bus/input/devices

# Should now show ELAN901C touchpad and ELAN0678 touchscreen

Check with libinput

# List all input devices recognized by libinput
libinput list-devices

# Should show both touchpad and touchscreen with capabilities

Test Functionality

Touchpad:

• Single finger: Cursor movement
• Two finger scroll: Vertical/horizontal scrolling
• Two finger tap: Right click
• Palm rejection: Should ignore accidental touches

Touchscreen:

• Single touch: Cursor movement and click
• Multi-touch: Pinch to zoom, two-finger gestures
• Touch accuracy: Should be precise across entire display

Auto-Load Configuration (If Needed)

If the module doesn't load automatically after reboot, create an auto-load config:

# Create module auto-load configuration
echo "i2c-hid-acpi" | sudo tee /etc/modules-load.d/i2c-hid.conf

# Verify
cat /etc/modules-load.d/i2c-hid.conf

Troubleshooting

Module Not Loading

# Try loading manually
sudo modprobe i2c-hid-acpi

# Check kernel messages
dmesg | grep -i "i2c.*hid\|elan"

Devices Not Recognized

# Check if devices are still on I2C bus
ls -la /sys/bus/i2c/devices/ | grep ELAN

# Check device status
cat /sys/bus/i2c/devices/i2c-ELAN901C:00/uevent
cat /sys/bus/i2c/devices/i2c-ELAN0678:00/uevent

Verify Kernel Config

# Check running kernel config
zcat /proc/config.gz | grep I2C_HID

# Should show:
# CONFIG_I2C_HID=m
# CONFIG_I2C_HID_ACPI=m

Files Modified/Created

Kernel Configuration

• /usr/src/linux/.config - Enabled CONFIG_I2C_HID_ACPI=m

Kernel Files

• /boot/vmlinuz-6.12.41-gentoo-x86_64 - New kernel (Nov 5 08:27)
• /boot/initramfs-6.12.41-gentoo-x86_64.img - New initramfs (Nov 5 08:41)
• /boot/System.map-6.12.41-gentoo-x86_64 - New symbol map

Backups

• /boot/vmlinuz-6.12.41-gentoo-x86_64.old - Automatic genkernel backup
• /boot/vmlinuz-6.12.41-gentoo-x86_64.backup-20251105 - Manual backup
• Similar for initramfs and System.map

Kernel Modules

• /lib/modules/6.12.41-gentoo-x86_64/kernel/drivers/hid/i2c-hid/i2c-hid-acpi.ko - New module

Configuration (to be created if needed)

• /etc/modules-load.d/i2c-hid.conf - Auto-load configuration (if needed)

Key Learnings

1. I2C HID ACPI is Essential: Modern laptops use I2C HID with ACPI binding for touchpads and touchscreens. Generic I2C HID support (CONFIG_I2C_HID) is not sufficient.

2. PNP0C50 = HID over I2C: The ACPI identifier PNP0C50 is the standard ID for devices using the HID over I2C protocol.

3. Module Dependencies:

   • i2c-hid-acpi depends on i2c-hid
   • Both must be enabled for ACPI-based I2C HID devices to work

4. Fast Incremental Rebuilds: Using --no-clean --no-mrproper with genkernel allows for fast incremental rebuilds when only adding a single module.

5. Device Detection vs Functionality: Devices can appear on the I2C bus (/sys/bus/i2c/devices/) but remain non-functional without the proper driver module.

References

• ACPI specification: PNP0C50 = HID over I2C Device
• Linux kernel: drivers/hid/i2c-hid/
• ELAN touchpad/touchscreen drivers: Built into i2c-hid-acpi module

Status

Current: ✅ WORKING - Both touchpad and touchscreen fully functional!

Verified:

• Touchpad cursor movement and multi-finger gestures working
• Touchscreen touch and multitouch input working
• Modules load automatically (i2c-hid-acpi)
• CONFIG_PINCTRL_AMD=y enabled and functional

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Last Updated: 2025-11-05 (Verified working after manual kernel compilation)