README: ACPI MADT Override Fix for MiTAC PH12LI (Intel i7-4770TE)

NOTICE

[Update] This issue is resolved upon applying D7340A06 BIOS update, but may affect older systems with similar architectures.

🛠️ Problem Summary

Systems based on the MiTAC PH12LI motherboard with Intel i7-4770TE CPUs exhibit a firmware bug in the ACPI MADT (APIC) table. When Hyper-Threading (HT) is enabled in BIOS:

• The BIOS only exposes 4 LAPIC entries (for physical cores) in the MADT.
• However, the SSDT/DSDT tables define 8 logical CPUs (CPU0–CPU7).
• This inconsistency causes Linux (RHEL 9) to boot with:
  • Missing logical CPUs
  • Unstable or frozen IRQs
  • Kernel hangs when using HT

This archive contains a workaround using an ACPI MADT override.

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✅ What’s Included

• apic.aml: Fixed ACPI MADT (APIC) table, exposing all 8 logical CPUs
• apic.dsl: Original editable source of the override (disassembled format)
• README.txt: This file

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🔧 Installation Instructions

1. Copy the apic.aml file

sudo mkdir -p /etc/acpi_override
sudo cp apic.aml /etc/acpi_override/apic.aml

2. Rebuild the initramfs (RHEL/CentOS)

sudo dracut -f

3. Apply required GRUB kernel parameters

sudo grubby --update-kernel=ALL --args="acpi_apic_instance=1 acpi_override"

4. Reboot the system

sudo reboot

5. Confirm the override was applied

dmesg | grep -i 'apic\|override'
lscpu

Look for:

• ACPI: Overriding APIC table via initrd
• 8 logical CPUs (lscpu shows CPU(s): 8)

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🧪 Verification

After reboot, run:

lscpu
cat /proc/interrupts
dmesg | grep -i acpi

You should see 8 CPUs and no interrupt or LAPIC errors.

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🛑 Reverting the Change

To undo:

sudo rm /etc/acpi_override/apic.aml
sudo dracut -f
sudo grubby --update-kernel=ALL --remove-args="acpi_apic_instance=1 acpi_override"

Then reboot normally.

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📝 Submission

This fix has been submitted to:

• https://bugzilla.redhat.com (Product: RHEL 9, Component: kernel)
• MiTAC support for firmware patch consideration
• Public Inbox

Bug Summary:

MiTAC PH12LI firmware exposes incomplete MADT APIC table with HT enabled; fixed via custom ACPI override.

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⚠️ Disclaimer

• CPU burst may cause system instability depending on voltage controls. To avert this issue, ensure that CPU frequency is reduced by 10% - for this particular system, this can be accomlished via:

echo 3210000 | sudo tee /sys/devices/system/cpu/cpu*/cpufreq/scaling_max_freq
sudo vim /etc/systemd/system/cpu-freq-max.service
sudo chmod 644 /etc/systemd/system/cpu-freq-max.service
sudo ln -s /etc/systemd/system/cpu-freq-max.service /etc/systemd/system/multi-user.target.wants/

Contents of cpu-freq-max.service:

[Unit]
Description=Set CPU Maximum Frequency
After=multi-user.target

[Service]
Type=oneshot
ExecStart=find /sys/devices/system/cpu -name "cpu*" -path "*/cpufreq/scaling_max_freq" -exec sh -c 'echo 3210000 > {}' \;
RemainAfterExit=yes

[Install]
WantedBy=multi-user.target

It is also recommended to set governor powercontrols to ondemand:

sudo vim /etc/systemd/system/cpu-governor.service
sudo chmod 644 /etc/systemd/system/cpu-governor.service
sudo ln -s /etc/systemd/system/cpu-governor.service /etc/systemd/system/multi-user.target.wants/

cpu-governor.service contents:

[Unit]
Description=Set CPU Governor to ondemand
After=multi-user.target

[Service]
Type=oneshot
ExecStart=/bin/bash -c 'echo ondemand > /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor'
RemainAfterExit=yes

[Install]
WantedBy=multi-user.target

Use at your own risk. This override patches a BIOS-level defect from userspace. It's intended for debugging and restoring expected CPU layout on Linux systems. Always keep a backup initramfs and test in a controlled environment.

Contributor Notes

Completion of this project could not be done without help from the ChatGPT Platform