November 19th, 2020


Acer Aspire Switch 10 E SW3-016's and SW5-012's and S1002's horrible EFI firmware

Recently I acquired an Acer Aspire Switch 10 E SW3-016, this device was the main reason for writing my blog post about the shim boot loop. The EFI firmware of this is bad in a number of ways:

  1. It considers its eMMC unbootable unless its ESP contains an EFI/Microsoft/Boot/bootmgfw.efi file.

  2. But it will actually boot EFI/Boot/bootx64.efi ! (wait what? yes really)

  3. It will only boot from an USB disk connected to its micro-USB connector, not from the USB-A connector on the keyboard-dock.

  4. You must first set a BIOS admin password before you can disable secure-boot (which is necessary to boot home-build kernels without doing your own signing)

  5. Last but not least it has one more nasty "feature", it detect if the OS being booted is Windows, Android or unknown and it updates the ACPI DSDT based in this!

Some more details on the OS detection mis feature. The ACPI "Device (SDHB) node for the MMC controller connected to the SDIO wifi module contains:

        Name (WHID, "80860F14")
        Name (AHID, "INT33BB")

Depending on what OS the BIOS thinks it is booting it renames one of these 2 to _HID. This is weird given that it will only boot if EFI/Microsoft/Boot/bootmgfw.efi exists, but it still does this. Worse it looks at the actual contents of EFI/Boot/bootx64.efi for this. It seems that that file must be signed, otherwise it goes in OS unknown mode and keeps the 2 above DSDT bits as is, so there is no _HID defined for the wifi's mmc controller and thus no wifi. I hit this issue when I replaced EFI/Boot/bootx64.efi with grubx64.efi to break the bootloop. grubx64.efi is not signed so the DSDT as Linux saw it contained the above AML code. Using the proper workaround for the bootloop from my previous blog post this bit of the DSDT morphes into:

        Name (_HID, "80860F14")
        Name (AHID, "INT33BB")

And the wifi works.

The Acer Aspire Switch 10 E SW3-016's firmware also triggers an actual bug / issue in Linux' ACPI implementation, causing the bluetooth to not work. This is discussed in much detail here. I have a patch series fixing this here.

And the older Acer Aspire Switch 10 SW5-012's and S1002's firmware has some similar issues:

  1. It considers its eMMC unbootable unless its ESP contains an EFI/Microsoft/Boot/bootmgfw.efi file

  2. These models will actually always boot the EFI/Microsoft/Boot/bootmgfw.efi file, so that is somewhat more sensible.

  3. On the SW5-012 you must first set a BIOS admin password before you can disable secure-boot.

  4. The SW5-012 is missing an ACPI device node for the PWM controller used for controlling the backlight brightness. I guess that the Windows i915 gfx driver just directly pokes the registers (which are in a whole other IP block), rather then relying on a separate PWM driver as Linux does. Unfortunately there is no way to fix this, other then using a DSDT overlay. I have a DSDT overlay for the V1.20 BIOS and only for the v1.20 BIOS available for this here.

Because of 1. and 2. you need to take the following steps to get Linux to boot on the Acer Aspire Switch 10 SW5-012 or the S1002:

  1. Rename the original bootmgfw.efi (so that you can chainload it in the multi-boot case)

  2. Replace bootmgfw.efi with shimia32.efi

  3. Copy EFI/fedora/grubia32.efi to EFI/Microsoft/Boot

This assumes that you have the files from a 32 bit Windows install in your ESP already.