TQMa8MPxL - YOCTO Linux BSP documentation

Since scarthgap.TQ.ARM.BSP.0003, the STKa8MPxL supports two display interfaces at a time when using the Mainline kernel.

By default HDMI and DP are activated, if a LVDS-Display is connected, additional work is required, as the 'DEFAULT' variable in the extlinux.conf needs to be changed to 'lvds'.
To do that, use nano /boot/extlinux/extlinux.conf to edit the file.

Using multiple displays, requires to identifiy the corresponding DRM (Direct Rendering Manager) cards.
To list available DRM card devices, use ls -l /sys/class/drm/.

The connector name will easily reveal the card number in question (e.g. HDMI-A-1 or LVDS-1).
DRM-devices without a connector are only rendering devices and cannot be used.

By default, Weston is configured for single display output. To enable the second display, the output devices must be explicitly configured.
The Weston service file can be edited using either systemctl edit weston.service or nano /usr/lib/systemd/system/weston.service.

The additional-devices parameter has to be added in the service file. The placeholders cardX (first display) and cardY (second display) needs to be adjusted according to the previously identified DRM cards:

[Service]
ExecStart=/usr/bin/weston --modules=systemd-notify.so --drm-device=cardX --additional-devices=cardY

Weston requires a restart after configuring using the commands systemctl daemon-reload and systemctl restart weston in sequence.
The daemon-reload is not required after editing the file with systemctl.

Both screens should now be active. To test the connection, use a mouse to switch betweeen the two monitors.