Windows on ARM devices

(Not to be confused with Windows Mobile devices)

Windows on ARM (Often abbreviated WoA) are a line of devices that were shipped with Windows as the operating system. Sometimes those devices are referred to as "Windows on Snapdragon" (WoS) as the majority is based on Qualcomm chipsets.

This page provides a general overview and common information for those devices in postmarketOS.

Installation

Installation on USB

1. Disable EFI secure boot.
2. Follow Pmbootstrap page, do a SD card installation to USB.

Installation on internal storage

WARNING: If you have a Windows recovery partition it is recommended to make a backup of it. Some vendors don't provide a recovery image. There is only one way to return to Windows on these devices: using dism utility with install.wim from recovery partition, so consider making a backup of this file.

Once you have a pmOS installation booted from USB:

Devices with UFS or NVME

1. Install pmbootstrap (apk add pmbootstrap).
2. Perform pmbootstrap install --disk /dev/sdX.

WARNING: X here represents a letter of block device, e.g. /dev/sda. Make sure to select correct, because selecting wrong one can lead to bricking your device. You can find the correct one with lsblk command. It should be the biggest one, usually the first.

Devices with EMMC

Compared to UFS devices where the OS has a dedicated LUN, or NVME devices, where the bootloader is stored on a separate chip, EMMC devices share bootloader setup similar to phones, where a set of partitions is dedicated for the UEFI and other things critical to boot.

WARNING: Altering contents or removing ANY partition apart from the EFI ESP, "Windows" ("C:") or "Windows recovery" may result in an unrecoverable brick!

One of the possible ways to install pmOS on such device would be to boot into pmOS usb install and overwrite "Windows" partition with root image, generated with pmbootstrap install --split, and overwrite the efi esp with the boot image.

Devices

Device	Codename	Chipset	CPU	GPU	Memory	Storage	Display	Supported in pmOS
Acer Aspire 1	acer-aspire1	Qualcomm Snapdragon 7c	2x Kryo 468 Gold + 6x Kryo 468 Silver	Adreno 618	4 GB	64 GB	1920x1080 IPS	Yes
Huawei MateBook E 2019	huawei-planck	Qualcomm Snapdragon 850 (SDM850)	4 × Qualcomm Kryo 3xx Gold, 4 × Qualcomm Kryo 3xx Silver	Adreno 630	8GB	256GB/512GB	2160x1440	Yes
Lenovo Flex 5G	lenovo-flex-5ga	Qualcomm Snapdragon 8cx	4x Kryo 495 Gold 2.84 GHz & 4x Kryo 495 Silver 1.8 GHz	Adreno 680	8 GB	256/512 GB	1920x1080 IPS	Yes
Lenovo ThinkPad X13s	lenovo-21bx	Qualcomm Snapdragon 8cx Gen 3 (SC8280XP)	4x 3.0GHz (Cortex-X1), 4x 2.4GHz (Cortex-A78)	Adreno 690	8GB, 16GB, 32GB	256GB, 512GB, 1TB	1920x1200 IPS	Yes
Lenovo Yoga 5G	lenovo-81xe	Qualcomm Snapdragon 8cx	4x Kryo 495 Gold 2.84 GHz & 4x Kryo 495 Silver 1.8 GHz	Adreno 680	8 GB	256/512 GB	1920x1080 IPS	Yes
Lenovo Yoga 5G	lenovo-82ak	Qualcomm Snapdragon 8cx	4x Kryo 495 Gold 2.84 GHz & 4x Kryo 495 Silver 1.8 GHz	Adreno 680	8 GB	256/512 GB	1920x1080 IPS	Yes
Lenovo Yoga 5G	lenovo-yoga-5g	Qualcomm Snapdragon 8cx	4x Kryo 495 Gold 2.84 GHz & 4x Kryo 495 Silver 1.8 GHz	Adreno 680	8 GB	256/512 GB	1920x1080 IPS	Yes
Lenovo Yoga C630	lenovo-yoga-c630	Qualcomm Snapdragon 850 (SDM850)	Octa-core (4x 2.9 GHz Kryo 385 Gold & 4x 1.7 GHz Kryo 385 Silver)	Adreno 630	8GB	128GB	1920x1080 IPS Touch + Stylus	Yes
Lenovo Yoga Slim 7x	lenovo-yoga-slim7x	Qualcomm Snapdragon 8 Elite (X1E80100)			32GB	1TB	2944x1840 OLED	Yes
Microsoft Windows Devkit 2023	volterra	Qualcomm Snapdragon 8cx Gen 3 (SC8280XP)	4x 3.0GHz (Cortex-X1), 4x 2.4GHz (Cortex-A78)	Adreno 690	32GB LPDDR4x	512GB M.2 2230 NVME SSD	Main: mDP (HBR2), Secondary and Tertiary: 2xUSB-C (HBR3)	No
Samsung Galaxy Book S	samsung-w767	Qualcomm Snapdragon 8cx	4x Kryo 495 Gold 2.84 GHz & 4x Kryo 495 Silver 1.8 GHz	Adreno 680	8 GB	256 GB	1920x1080 IPS	Yes

Common issues and quirks

• It's generally unfeasible to use original vendor ACPI code shipped with the existing Qualcomm devices to boot Linux since significant part of the hardware information is baked into the windows drivers code, instead of the ACPI. Thus, the usual way of using Linux on these devices assumes booting with the Device Tree made for the device.

Virtualization support

Due to a quirk in firmware on Windows-on-Snapdragon devices it's impossible to use virtualization by default as the system boots in EL1. Windows uses special "Secure launch" mechanism to elevate to EL2 as part of the bootloader flow and gain virtualization support for hyper-v.

slbounce is an alternative "Secure launch" implementation that can allow one to boot Linux (or other OS) in EL2 and unlock virtualization. Unfortunately linux can't yet use all of the device features when running EL2 so, for example, things that rely on remoteprocs will not work.

Prerequisites

• Make sure Windows reports virtualization as enabled;
• Get tcblaunch.exe from the windows install on your device. You can find it in C:\Windows\system32\tcblaunch.exe;
• Be able to boot into EFI Shell.

Setup

Clone and build slbounce.

$ git clone --recursive https://github.com/TravMurav/slbounce.git
$ git checkout switch-if-overlay
$ cd slbounce
$ make -j$(nproc)
$ make -j$(nproc) dtbs

Copy out/*.efi and your tcblaunch.exe to the root of your ESP (or a usb stick). Make sure tcblaunch.exe is in the root of the same disk as slbounce.efi and sltest.efi.

Check that your device is supported by slbounce: Reboot into EFI Shell and run sltest.efi:

fs0:\> sltest.efi tcblaunch.exe

Your device should show a green line on the top of the screen. Reboot it by holding the power button.

Generate a special EL2 dtb by applying overlays from slbounce to your device's dtb:

$ cd slbounce
# fdtoverlay -i /boot/sc7180-acer-aspire1.dtb -o /boot/sc7180-acer-aspire1-el2.dtb out/dtbo/sc7180-symbols.dtbo out/dtbo/sc7180-el2.dtbo

(Note that the order of overlays is meaningful)

Add a new boot option by copying existing one and changing the name and devicetree file and install slbounce to systemd-boot driver dir:

$ sudo cat /boot/loader/entries/pmos_el2.conf
title	   postmarketOS (EL2)
sort-key   yyy-postmarketOS-el2
linux	   linux.efi
initrd	   initramfs
options    efi=novamap,noruntime deferred_probe_timeout=30 console=tty0
devicetree sc7180-acer-aspire1-el2.dtb

$ sudo cat /boot/loader/loader.conf
default  pmos.conf
timeout  1

$ sudo cp out/slbounce.efi /boot/EFI/systemd/drivers/slbounceaa64.efi

Now you should see two boot options on each boot, where EL2 boot option would allow you to use virtualization (however some other features of the device may be broken).

See also

• Non-distro-specific IRC room for Linux on ARM laptops: #aarch64-laptops on OFTC. Public archive.