This repository contains a number of patches for the ACPI DSDT table of the ASUS MeMO Pad 7 (ME176C/CX).
IMPORTANT NOTE: The patches in this repository are no longer necessary to run properly on recent Linux kernel versions.
Similar workarounds were integrated into the x86-android-tablets Linux kernel module that works without having to modify
the ACPI tables.
Unfortunately, ASUS decided to add workarounds to the kernel instead of fixing the ACPI tables using a BIOS update. Most of these workarounds are for the ACPI DSDT table, which contains information about the hardware of the tablet, e.g. where to find certain I/O ports. Obviously, this doesn't work well when using an upstream kernel.
Originally, I started adding similar workarounds in the kernel, but as they grew they became rather annoying to maintain. Eventually, when attempting to get Bluetooth working, I run into a problem that wasn't easy to workaround directly in kernel code without a lot of ugly hacks.
Consequently, I decided to fork the ACPI DSDT table where these mistakes have been made, and update it with the necessary fixes. The kernel loads the fixed table at runtime and overrides the original one from the BIOS. This is potentially dangerous, and can easily break things (or even hardware), but it has shown to work quite well.
Requirements: me176c-boot or at least the me176c-boot bootstrap (can be used with other bootloaders)
The modified ACPI DSDT table (dsdt.asl) is compiled using iASL (part of ACPICA).
iasl should be available as package (iasl or acpica) in most Linux distributions.
See Upgrading ACPI tables via initrd of the Linux kernel documentation for an introduction how to compile and load in in your Linux kernel.
The ACPI DSDT table appears to be equal on all ASUS MeMO Pad 7 (ME176C/CX) devices. The only difference is a memory address to the global NVS (GNVS) area, which is dynamically allocated and therefore differs from device to device. Normally, this address would need to be updated for each device before compilation. This makes sharing the compiled version impossible.
Example:
OperationRegion (GNVS, SystemMemory, 0x395FEA98, 0x0340) // Device 1
OperationRegion (GNVS, SystemMemory, 0x395F1A98, 0x0340) // Device 2I used to handle this using an out-of-tree kernel patch that remapped this address at runtime. However, I have been looking for alternative options so the ACPI DSDT override can also be used on mainline kernels.
After a lot of consideration I came up with a solution that handles this within the bootloader,
specifically within the "bootstrap" loader in me176c-boot. The DSDT table no longer contains the GNVS address.
Instead, it loads an extra OEM6/GNVS ACPI table that contains only the dynamic GNVS address.
This makes it possible to have one static compiled DSDT table, but still load the GNVS address dynamically.
Also see: https://github.com/me176c-dev/me176c-boot/commit/b50b460e92d46efab743fc1e1df47935f7755f39
dsdt.dsl is a disassembled version of the original ACPI DSDT table using iASL.
The original table and the BIOS implementation of the tablet are not open-source, so it should not be considered to be under
an open-source license.
Only my changes (see commit history) can be reproduced under the terms and conditions of the MIT License:
MIT License
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