Based upon initial work posted by Stefan Grundmann <sg2342@googlemail.com> to
freebsd-hackers and later posted here for review on https://reviews.freebsd.org/D34221,
this is one of three patches adding support for non-native panel orientation to
the vt(4) console
The other two patches add similar support to /boot/loader and to the drm module.
Each of these patches may be applied separately or not, but consistent
rotation through all phases of bootstrapping and running the system console
will require all three.
The screen orientation is set by adding
screen.rotate="angle"
to /boot/loader.conf. The drm-kms driver has independent support for
discovering the correct orientation through BIOS flags (which are, however,
not yet in much use by manufacturers) and through (unimplemented on FreeBSD)
quirk tables. Once KMS is loaded, if it discovers the correct panel orientation,
the screen orientation will be set without the loader.conf setting.