qemu: add a hint on how to enable CPU render nodes when a suitable GPU is absent
This is particularly useful for llvm-accelerated GL rendering from qemu guest to
an offscreen buffer (accessible over vnc or spice) using llvmpipe on the
host, rather than using unaccelerated swrast renderer in the guest.
This is the best that can be done in the absence of a host GPU with render node
support (such as old Matrox cards common in servers, or fully virtualized cloud
environments with no GPU at all).
Note: even though NVidia blob drivers do support render nodes, they do not
support gbm (yet?), and so rendering will fall back to llvmpipe as well even when
the system has a 3000 euro NVidia GPU. Cue Linus picture.
Signed-off-by: Alexander Kanavin <alex.kanavin@gmail.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
