surface-dial-linux

A Linux userspace controller for the Microsoft Surface Dial. Requires Linux Kernel 4.19 or higher.

Bug reports and PRs are appreciated!

Overview

surface-dial-daemon receives raw events from the surface dial and translates them to more conventional input events.

The daemon uses FreeDesktop notifications to provide visual feedback when switching between actions.

It would be cool to create some sort of GUI overlay (similar to the Windows one), though that's out of scope at the moment.

Operating Modes

Holding down the button for ~750ms will open up a meta-menu (using FreeDesktop notifications) which allows you to switch between operating modes on-the-fly. The daemon persists the last selected mode on-disk, so if you only care about one mode (e.g: scrolling), you can just set it and forget it.

Modes in bold should be considered EXPERIMENTAL. They seem to work alright (some of the time), but they would really benefit from some more polish / bug fixes.

Mode	Click	Rotate	Notes
Scroll	-	Scroll	Fakes chunky mouse-wheel scrolling ¹
Scroll (Fake Multitouch)	Reset Touch Event	Scroll	Fakes smooth two-finger scrolling
Zoom	-	Zoom
Volume	Mute	Volume
Media	Play/Pause	Next/Prev Track
Media + Volume	Play/Pause	Volume	Double-click = Next Track
Paddle Controller	Space	Left/Right Arrow Key	Play arkanoid as the devs intended!

¹ At the time of writing, almost all Linux userspace programs don't take advantage of the newer high-resolution scroll wheel events, and only support the older, chunkier scroll wheel events. Check out this blog post for more details.

Custom Modes

At the moment, all modes (along with their meta-menu ordering) are hard-coded into the daemon itself.

If you don't mind hacking together a bit of [very simple] Rust code, adding new modes should be fairly straightforward - just add a new ControlMode implementation under src/controller/controls and instantiate it in main.rs.

If you ended up implementing new mode you think others would find useful, please consider upstreaming it!

Building

Building surface-dial-daemon requires the following:

Linux Kernel 4.19 or higher
A fairly recent version of the Rust compiler
libudev
libevdev
hidapi

You can install Rust through rustup.

Unless you're a cool hackerman, the easiest way to get libudev, libevdev, and hidapi is via your distro's package manager.

# e.g: on ubuntu
sudo apt install libevdev-dev libhidapi-dev libudev-dev

On certain Ubuntu distros, you may also need to install the librust-libdbus-sys-dev package:

sudo apt install librust-libdbus-sys-dev

Once those are installed, surface-dial-daemon can be built using the standard cargo build flow.

cargo build -p surface-dial-daemon --release

The resulting binary is output to target/release/surface-dial-daemon

Running

The daemon is able to handle the dial disconnecting/reconnecting, so as long as it's running in the background, things should Just Work:tm:.

Note that the daemon must run as a user process (not as root), as it needs access to the user's D-Bus to send notifications.

Having to run as a user process complicates things a bit, as the daemon must be able to access several restricted-by-default devices under /dev/. Notably, the /dev/uinput device and the Surface Dial's /dev/hidrawX device will need to have their permissions changed for things to work correctly. The proper way to do this is using the included udev rules, though if you just want to get something up and running, sudo chmod 666 <device> should work fine (though it will revert back once you reboot!).

See the Installation section below for how to set up the permissions / udev rules.

During development, the easiest way to run surface-dial-linux is using cargo:

cargo run -p surface-dial-daemon

Alternatively, you can run the daemon directly using the executable at target/release/surface-dial-daemon.

Installation

I encourage you to tweak the following setup procedure for your particular Linux configuration.

The following steps have been tested working on Ubuntu 20.04/20.10.

# Install the `surface-dial-daemon` (i.e: build it, and place it under ~/.cargo/bin/surface-dial-daemon)
# You could also just copy the executable from /target/release/surface-dial-daemon to wherever you like.
cargo install --path .

# add self to the existing /dev/input group (either `input` or `plugdev`, depending on your distro)
sudo gpasswd -a $(whoami) $(stat -c "%G" /dev/input/event0)

# install the systemd user service
mkdir -p ~/.config/systemd/user/
cp ./install/surface-dial.service ~/.config/systemd/user/surface-dial.service

# install the udev rules
sudo cp ./install/10-uinput.rules /etc/udev/rules.d/10-uinput.rules
sudo cp ./install/10-surface-dial.rules /etc/udev/rules.d/10-surface-dial.rules

# reload systemd + udev
systemctl --user daemon-reload
sudo udevadm control --reload

# enable and start the user service
systemctl --user enable surface-dial.service
systemctl --user start surface-dial.service

To see if the service is running correctly, run systemctl --user status surface-dial.service.

You may need to reboot to have the various groups / udev rules propagate. You may also need to change DisableSecurity to DisableSecurity=true in /etc/bluetooth/network.conf to successfully pair the Surface Dial.

If things aren't working, feel free to file a bug report!

Call for Contributors: It would be awesome to have a proper packaging pipeline set up as well (e.g for deb/rpm).

Implementation Notes

Core functionality is provided by the following libraries.

libudev to monitor when the dial connects/disconnects.
libevdev to read events from the surface dial through /dev/input/eventXX, and to fake input through /dev/uinput.
hidapi to configure dial sensitivity + haptics.
notify-rust to send desktop notifications over D-Bus.

The code makes heavy use of threads + channels to do non-blocking event handling. While async/await would have been a great fit for an application like this, I optimized for getting something up-and-running rather than maximum performance. Plus, the Rust wrappers around libudev, libevdev, and hidapi don't have native async/await support, so it would have been a lot more work for not too much gain.

The codebase is reasonably well organized, aside from the dial_device implementation, which is admittedly a bit gnarly. There's a bit of of thread/channel spaghetti going on to ensure that the lifetime of the haptics object lines up with the lifetime of the libevdev objects (as reported by libudev). All things considered, it's not too messy, but it could certainly use some cleanup. Fortunately, if you're only interested in implementing new operating modes, you won't have to worry about any of that, as all the nitty-gritty device interaction is neatly encapsulated behind the ControlMode trait.

Feature Roadmap

This is a rough outline of features I'd like to see implemented in this daemon. There's a non-zero chance that at some point the daemon will be "good enough" for me, and some features will be left unimplemented.

Contributions are more than welcome!

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A Linux userspace controller for the Microsoft Surface Dial. Requires Linux Kernel 4.19 or higher.

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