|WESTON-DRM(7)||Miscellaneous Information Manual||WESTON-DRM(7)|
weston-drm - the DRM backend for Weston
The DRM backend is the native Weston backend for systems that support the Linux kernel DRM, kernel mode setting (KMS), and evdev input devices. It is the recommended backend for desktop PCs, and aims to provide the full Wayland experience with the "every frame is perfect" concept. It also relies on the Mesa GBM interface.
With the DRM backend, weston runs without any underlying windowing system. The backend uses the Linux KMS API to detect connected monitors. Monitor hot-plugging is supported. Input devices are found automatically by udev(7). Compositing happens mainly in GL ES 2, initialized through EGL. It is also possible to take advantage of hardware cursors and overlays, when they exist and are functional. Full-screen surfaces will be scanned out directly without compositing, when possible. Hardware accelerated clients are supported via EGL.
The backend chooses the DRM graphics device first based on seat id. If seat identifiers are not set, it looks for the graphics device that was used in boot. If that is not found, it finally chooses the first DRM device returned by udev(7). Combining multiple graphics devices is not supported yet.
The DRM backend also supports virtual outputs that are transmitted over an RTP session as a series of JPEG images (RTP payload type 26) to a remote client. Virtual outputs are configured in the remote-output section of weston.ini.
The DRM backend uses the following entries from weston.ini.
- Sets the default pixel format for DRM KMS framebuffers. Format can
be xrgb8888, xrgb2101010, rgb565 or others. Weston
recognizes the names of most pixel formats defined by the kernel DRM
subsystem in drm_fourcc.h header without the DRM_FORMAT_ prefix.
The actually supported pixel formats depend on the DRM driver and
hardware, and the renderer used. Using Pixman-renderer, DRM-backend
supports xrgb8888, xrgb2101010, rgb565 and some of
their permutations. The formats supported with GL-renderer depend on the
EGL and OpenGL ES 2 or 3 implementations. The names are case-insensitive.
This setting applies only to outputs in SDR mode, see eotf-mode in
If not specified, xrgb8888 is used. See also gbm-format in output section.
- sets Weston's pageflip timeout in milliseconds. This sets a timer to exit gracefully with a log message and an exit code of 1 in case the DRM driver is non-responsive. Setting it to 0 disables this feature.
- The KMS connector name identifying the output, for instance LVDS1.
- Specify the video mode for the output. The argument mode can be one of the words off to turn the output off, preferred to use the monitor's preferred video mode, or current to use the current video mode and avoid a mode switch. It can also be a resolution as:
- Specify a mode with a given refresh-rate measured in Hz.
- mode=widthxheight@refresh_rate ratio
- Here ratio is Picture Aspect-Ratio which can have values as 4:3,
16:9, 64:27, and 256:135. This resolution-format helps to select a CEA
mode, if such a video mode is present in the mode-list of the output.
CEA defines the timing of a video mode, which is considered as a standard for HDMI spcification and compliance testing. It defines each and every parameter of a video mode, like hactive, vactive, vfront, vback etc., including aspect-ratio information. For CEA modes, the drm layer, stores this aspect-ratio information in user-mode (drmModeModeInfo) flag bits 19-22. For the non-CEA modes a value of 0 is stored in the aspect-ratio flag bits.
Each CEA-mode is identified by a unique, Video Identification Code (VIC). For example, VIC=4 is 1280x720@60 aspect-ratio 16:9. This mode will be different than a non-CEA mode 1280x720@60 0:0. When the video mode 1280x720@60 0:0 is applied, since its timing doesn't exactly match with the CEA information for VIC=4, it would be treated as a non-CEA mode. Also, while setting the HDMI-AVI-Inforframe, VIC parameter will be given as '0'. If video mode 1280x720@60 16:9 is applied, its CEA timimgs matches with that of video mode with VIC=4, so the VIC parameter in HDMI-AVI-Infoframe will be set to 4.
Many a times, an output may have both CEA and non-CEA modes, which are similar in all resepct, differing only in the aspect-ratio. A user can select a CEA mode by giving the aspect-ratio, along with the other arguments for the mode. By omitting the aspect-ratio, user can specify the non-CEA modes. This helps when certification testing is done, in tests like 7-27, the HDMI-analyzer applies a particular CEA mode, and expects the applied mode to be with exactly same timings, including the aspect-ratio and VIC field.
The resolution can also be a detailed mode line as below.
- mode=dotclock hdisp hsyncstart hsyncend htotal vdisp vsyncstart vsyncend vtotal hflag vflag
- Use the given detailed mode line as the video mode for this output. The definition is the same as in xorg.conf(5), and cvt(1) can generate detailed mode lines.
- Transform for the output, which can be rotated in 90-degree steps and possibly flipped. Possible values are normal, rotate-90, rotate-180, rotate-270, flipped, flipped-rotate-90, flipped-rotate-180, and flipped-rotate-270.
- Set the DRM KMS framebuffer format for this specific output. If not set, the value from gbm-format option in core section is used for SDR mode outputs and xrgb2101010 for other modes. For the possible values for format see gbm-format option in core section. For SDR mode, see eotf-mode in weston.ini(7).
- If using the Pixman-renderer, use shadow framebuffers. Defaults to true.
- Make this output (connector) a clone of another. The argument name
is the name value of another output section. The referred to output
section must exist. When this key is present in an output section, all
other keys have no effect on the configuration.
NOTE: cms-colord plugin does not work correctly with this option. The plugin chooses an arbitrary monitor to load the color profile for, but the profile is applied equally to all cloned monitors regardless of their properties.
- Force the output to be enabled even if the connector is disconnected. Defaults to false. Note that mode=off will override force-on=true. When a connector is disconnected, there is no EDID information to provide a list of video modes. Therefore a forced output should also have a detailed mode line specified.
- Set "max bpc" KMS property to value N, silenty clamped to the hardware driver supported range. This artificially limits the driver chosen link bits-per-channel which may be useful for working around sink hardware (e.g. monitor) limitations. The default is 16 which is practically unlimited. If you need to work around hardware issues, try a lower value like 8. A value of 0 means that the current max bpc will be reprogrammed.
- Specify unique name for the output.
- Specify the video mode for the output. The argument mode is a resolution setting, such as:
- If refresh_rate is not specified it will default to a 60Hz.
- Specify the host name or IP Address that the remote output will be transmitted to.
- Specify the port number to transmit the remote output to. Usable port range is 1-65533.
- Specify the gstreamer pipeline. It is necessary that source is appsrc, its name is "src", and sink name is "sink" in pipeline. Ignore port and host configuration if the gst-pipeline is specified.
When the DRM backend is loaded, weston will understand the following additional command line options.
- By default, use the current video mode of all outputs, instead of switching to the monitor preferred mode.
- Use the DRM device cardN instead of the default heuristics based on seat assignments and boot VGA status. For example, use card0.
- Use graphics and input devices designated for seat seatid instead of the seat defined in the environment variable XDG_SEAT. If neither is specified, seat0 will be assumed.
- Allow Weston to start without input devices. Used for testing purposes.