Mir graphics support¶
This document describes the requirements for running Mir.
Mir supports graphics and input “platforms” by using modules loadable at runtime. This means that applications built with Mir can run across a range of graphics stacks.
There are Mir platforms supplied with Mir and the potential to develop more. There is also one platform we know of developed by a third party.
The most widely used and tested platform is “mesa-kms” which works with the Mesa collection of open-source graphics drivers. That’s used on Intel-graphics based desktops and a variety of SBCs and other devices.
Summary list of current Mir graphics platforms¶
Platform |
Status |
Description |
|---|---|---|
gbm-kms |
Released |
Works with any driver providing KMS, |
x11 |
Released |
Provides “Mir-on-X11” primarily for development. |
eglstream-kms |
Released |
Works with proprietary Nvidia drivers. |
wayland |
Released |
Provides “Mir-on-Wayland” both for nested compositors and for development. |
android |
Released |
3rd party (UBports) works with a libhybris container for Android drivers. (Typically for phone hardware with Android-only drivers.) |
dispmanx |
Released |
Works with Broadcom proprietary DispmanX API. |
Each of these platforms depends on having the corresponding kernel and userspace drivers installed on the system. On startup Mir will “probe” the system for support of the above and select the best supported platform.
Choosing hardware and drivers¶
When configuring a system for use with Mir it is not only necessary to check the hardware and drivers for compatibility with Mir, but also with the application software.
For example, if the application software uses 3D or video acceleration, then that needs to be supported by the application (possibly through a supporting library) on the selected drivers and hardware. It is very possible that the support differs between the open-source drivers and the proprietary ones. Video decoding, in particular, varies a lot between graphics stacks.
There’s a further complication in that Mir expects applications to use Wayland and some features on some drivers don’t work with Wayland. (An example is that the intel-vaapi-driver for Ubuntu 18.04 doesn’t work with Wayland. That is fixed in more recent versions, but may need to be addressed for core18 snaps.)
Also, there are applications that do not support Wayland directly. These can be supported with Xwayland - a program that translates from X11 to Wayland for the application. But that leads to further limitations as the GL acceleration support through Xwayland depends upon the graphics drivers. It works with Intel on Mesa, but beyond that it is patchy.
Some hardware examples¶
RPi 3¶
GPU: VideoCore IV
Mesa open-source graphics stack |
Proprietary driver |
|---|---|
VC4 - open source kernel/mesa stack. |
Dispmanx - Broadcom proprietary(ish) stack. |
Mir works, and is tested on this. |
Mir works, not yet incorporated into CI lab testing |
Supports GL. |
Requires out-of-tree patches to https://github.com/raspberrypi/userland to enable 3D and video decode clients. |
Does not support OMX. |
Potentially higher performance (particularly OMX for video decode) |
As a mesa/gbm-based platform, would expect 3D to work in XWayland. |
As a non-mesa/gbm platform would likely not have 3D (or video decode) in XWayland. |
i.MX6¶
GPU: Vivante GC something (varies by model)
Mesa open-source graphics stack |
Proprietary driver |
|---|---|
Etnaviv - Full open-source stack, using standard KMS/dma-buf/gbm interfaces. Reverse-engineered. |
Vivante - proprietary driver. |
Mir would use same platform as on the desktop - gbm-kms. |
Would require writing a Mir platform (this is clearly possible; there are patches for Weston to support vivante) |
Supports 3D (mesa GL) + video decoding (CODA v4l2) |
Supports 3D + video decoding |
Performance may be an issue (for example, https://github.com/Igalia/meta-webkit/issues/13) |
Performance may be better; supported by downstream projects (again, cf: https://github.com/Igalia/meta-webkit/wiki/i.MX6) |
Notably - the open source stack should provide 3D acceleration (and potentially video acceleration) in XWayland. |
Support for 3D in XWayland is unknown; would likely require significant out-of-tree patches. |
i.MX8¶
GPU: Vivante GC7000
Mesa open-source graphics stack |
Proprietary driver |
|---|---|
Etnaviv - Full open-source stack, using standard KMS/dma-buf/gbm interfaces. Reverse-engineered. |
Vivante - proprietary driver. |
Same comments as etnaviv on i.MX6 apply, but the GPU is newer and the driver support is likewise newer; there may be more missing features/bugs than i.MX6 support. |
same comments as i.MX6. |
Looks like there might not be open-source video decode support (https://community.nxp.com/t5/i-MX-Processors/i-MX8-Linux-video-decode-support/m-p/796955/highlight/true#M123321). Unknown whether we could interface the IMX bits with the etnaviv DRM bits. |
Proprietary video decode solution. |
Driver requirements¶
Different Mir platforms require different features of the underlying driver stack. The features needed to enable a given Mir platform are:
gbm-kms¶
The gbm-kms platform requires a DRM device node with KMS support, a libgbm implementation for buffer allocation, and an EGL implementation supporting at least EGL_KHR_platform_gbm (or the equivalent EGL_MESA_platform_gbm extension) and EGL_WL_bind_wayland_display.
Optionally, the EGL implementation can support EGL_EXT_image_dma_buf_import, EGL_EXT_image_dma_buf_import_modifiers, and use the zwp_linux_dmabuf_unstable_v1 Wayland protocol for client buffer transfer. Support for this was added in Mir 2.3. Composite-bypass support depends on this implementation. Some future performance improvements, such as overlay plane usage, are likely to require this support from the driver stack.
eglstream-kms¶
The eglstream-kms platform requires a DRM device node with Atomic KMS support and an EGL implementation supporting EGL_EXT_platform_base, EGL_EXT_platform_device, EGL_EXT_device_base, EGL_EXT_device_drm, and EGL_EXT_output_base.