Wayland Weston support on Jetson platforms

Support for Wayland/Weston has been adapted from the open-source libraries and patches that NVIDIA has published, rather than using the binary-only libraries packaged into the L4T BSP.

DRM/KMS support

Starting with L4T R32.2.x, DRM/KMS support in the BSP is provided through a combination of a custom libdrm.so shared library and the tegra-udrm kernel module. The library intercepts some DRM API calls; any APIs it does not handle directly are passed through to the standard implementation of libdrm.

Builds that include weston will also include a configuration file (via the tegra-udrm-probeconf recipe) that loads the tegra-udrm module with the parameter modeset=1. This enables KMS support in the L4T-specific libdrm library. If your build includes a different Wayland-based compositor, you may also need to include this configuration file.

(Earlier versions of L4T used a different custom libdrm implementation that had no KMS support and was not ABI-compatible with the standard libdrm implementation.)

Mesa build changes

The Mesa build has been changed to enable libglvnd support, which creates the necessary vendor plugins of the EGL and GLX libraries and packages them as libegl-mesa and libgl-mesa.

xserver-xorg changes

The xserver-xorg build has also been changed to disable DRI and KMS support on Tegra platforms.

libglvnd

Starting with L4T R32.1, the BSP uses libglvnd rather than including pre-built copies of the OpenGL/EGL/GLES libraries.

egl-wayland

The egl-wayland extension is built from source, with an additional patch to correct an issue with detecting Wayland displays and surfaces. The recipe also installs the needed JSON file so that the extension can be found at runtime.

weston-eglstream

NVIDIA's patches for supporting Weston using the EGLStream/EGLDevice backend are maintained in this repository. As of L4T R32.2.x, no additional Tegra-specific patches are required.

The --use-egldevice option gets added to the command line when starting Weston to activate this support.

Note that support for the EGLStream backend was dropped in Weston 10 in favor of using GBM. We supply a backend for libgbm that uses NVIDIA's libnvgbm.so manage GBM objects, and we still patch Weston support the EGLStream protocol for Wayland clients.

XWayland

XWayland appears to work, but hardware-accelerated OpenGL (through the libGLX_nvidia provider) is not available.

Testing

The following tests are performed:

1. Verify that core-image-weston builds.
2. Verify that weston starts at boot time.
3. Verify that weston sample programs, such as weston-simple-egl, display appropriate output.
4. Verify that the nveglglessink gstreamer plugin works with the winsys=wayland parameter by running a gstreamer pipeline to display an H.264 video. Note that the DISPLAY environment variable must not be set, per the NVIDIA documentation.
5. Verify that the l4t-graphics-demos applications work.

Troubleshooting

The following commands work on a Jetson TX2 and probably others:

Turn off HDMI:

echo -1 > /sys/kernel/debug/tegra_hdmi/hotplug
echo 4 > /sys/class/graphics/fb0/blank

(Source)

Turn on HDMI:

echo 1 > /sys/kernel/debug/tegra_hdmi/hotplug
echo 0 > /sys/class/graphics/fb0/blank

(Source)

Reading HDMI connection state:

/sys/devices/virtual/switch/hdmi/state is 0 when disconnected and 1 when connected. (Source)