Update (14 May 2022)

For amdgpu please use upstream DisplayLink repository (https://github.com/DisplayLink/evdi). This branch will be retired.

Extensible Virtual Display Interface

For Gnome/Wayland please use upstream EVDI: https://github.com/DisplayLink/evdi

The hack-fix for slow screen update on AMD/DisplayLink screens

The EVDI driver uses CPU to copy framebuffer. In order to make that copy fast the CPU requires cached access to the buffer. This is the case for integrated Intel GPU's. In case of AMD APU's (e.g. Ryzen 4750U) and most discrete GPU's the access to the framebuffer is uncached. Hence the copy is very slow. This branch is a hack-fix. It ignores AMDGPU driver and provides direct cached CPU access to the framebuffer. This is NOT A CORRECT way to implement it as the AMDGPU driver should be responsible for managing its memory. Although it seems to work with the latest kernels, users mileage may vary (crashes have been reported). It should only be tried on AMD APU's (not discrete GPU's).

Gnome/Wayland circumvents the problem described above by commanding the GPU to perform additional copy of the framebuffer which is then fed into EVDI. That buffer is cached and can be copied without hassle by EVDI. There are however two framebuffer copies instead of one which can affect performance. X11 does not implement such a work-around.

How to use it.

(make sure you know how to revert it in case it does not work)

With DKMS version >= 2.8.2

(Note: a distribution's dkms binary can be upgraded: https://github.com/dell/dkms/)

This will allow the EVDI module to be automatically built, signed (if using Secure Boot), and installed during kernel upgrades.

1. Install latest DisplayLink driver, get your DisplayLink screen to work (although with slow update rate)
2. Clone this repo and checkout this branch: amd_vmap_texture
3. copy files from module dir into /usr/src/evdi* (highest version) dir
4. Run: sudo dkms uninstall evdi/version
   sudo dkms unbuild evdi/version
   sudo dkms build evdi/version
   sudo dkms install evdi/version
5. append "vmap_texture=1" to /etc/modprobe.d/evdi.conf (the content of the file should look like this "options evdi initial_device_count=4 vmap_texture=1")
6. reboot.

A shell script to automate this process was contributed by dkebler and can be found as evdi-install.sh.

With DKMS version < 2.8.2

(Note: The EVDI module will need to be replaced after each kernel upgrade. If secure boot is enabled, the .ko file will need to be signed.)

1. Install latest DisplayLink driver, get your DisplayLink screen to work (although with slow update rate)
2. Clone this repo and checkout this branch: amd_vmap_texture
3. Build the kernel module (cd evdi/module, then make) If secure boot is enabled, sign evdi.ko now.
4. sudo modinfo evdi (to get the location of the running kernel module)
5. sudo cp ./evdi.ko (location from #4)
6. append "vmap_texture=1" to /etc/modprobe/evdi.conf (the content of the file should look like this "options evdi initial_device_count=4 vmap_texture=1")
7. reboot.

The Extensible Virtual Display Interface (EVDI) is a Linux® kernel module that enables management of multiple screens, allowing user-space programs to take control over what happens with the image. It is essentially a virtual display you can add, remove and receive screen updates for, in an application that uses the libevdi library.

The project is part of the DisplayLink Ubuntu development which enables support for DisplayLink USB 3.0 devices on Ubuntu. Please note that this is NOT a complete driver for DisplayLink devices. For more information and the full driver package, see DisplayLink Ubuntu driver.

This open-source project includes source code for both the evdi kernel module and a wrapper libevdi library that can be used by applications like DisplayLink's user mode driver to send and receive information from and to the kernel module.

How to use

See libevdi API documentation for details.

EVDI is a driver compatible with a standard Linux DRM subsystem. Due to this, displays can be controlled by standard tools, eg. xrandr or display settings applets in graphical environments eg. Unity, Gnome or KDE.

Minimum supported kernel version required is 4.15. DisplayLink have checked the module compiles and works with Ubuntu variants of kernels up to 5.5. Although other vanilla Linux kernel sources are used for Travis CI job, newer kernels, or kernel variants used by other distributions may require extra development. Please see below to see how you can help.

Future Development

This is a first release. DisplayLink are open to suggestions and feedback on improving the proposed architecture and will gladly review patches or proposals from the developer community. Please find a current list of areas we identify as requiring attention below.

• Compatibility with distributions other than Ubuntu 18.04/20.04 LTS is not verified. Please let us know if you make it work on other distros - pull requests are welcome!
• The communication between the EVDI kernel module and the wrapper libevdi library is not access-controlled or authenticated. This could be improved in future releases, making it harder to compromise the data EVDI is sending and receiving.
• EVDI kernel module driver is currently a platform_driver, for multiple reasons; most importantly because virtual displays are not discoverable, i.e. cannot be enumerated at the hardware level. EVDI is also a generic device, not tied to any particular kind of device, transport layer or a bus.

Licensing

Please refer to the LICENSE information in module and library subfolders of this project.

More information

For more information, see our support page. Visit displaylink.com to learn more about DisplayLink technology.

© Copyright 2015-2020 DisplayLink (UK) Ltd.

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