Passing multi-screen layout to KMS driver

Michael Thayer michael.thayer at
Fri Dec 16 11:33:44 UTC 2016

Adding Dave on CC here as the original creator of the suggested X and Y 

15.12.2016 15:03, Michael Thayer wrote:
> 14.12.2016 11:11, Gerd Hoffmann wrote:

[Summary of cut text: VirtualBox and Qemu use emulated graphics tablets 
to pass the host pointer through to the guest.  X.Org and GNOME 
Shell/Wayland map the tablet range to cover the whole virtual desktop, 
but GNOME Shell/Wayland does not provide any way for the host to 
discover the layout of that desktop in order to map positions in host 
windows to positions on guest screens.]

>>> So I would be interested to know whether anyone else has thought about
>>> this problem, and possibly even about an interface to let the compositor
>>> pass the information.  If not, would people be open to the idea?  I
>>> would much rather have something generally agreed on than hack
>>> something up.
> [...]  It would be
> nice though as I said if the compositor (or whoever is controlling the
> display) could just provide the layout information to the driver itself.
>  We already have "suggested X" and "suggested Y" for the other
> direction, and for now I have solved it by always providing "suggested
> X" and "suggested Y" hints in the driver.

My idea is to submit a patch which removes the DRM_MODE_PROP_IMMUTABLE 
flag from the suggested X and Y connector properties (with appropriate 
documentation), so that the compositor can use them to tell the driver 
about the layout.  It would be greatly appreciated if someone could tell 
me if that is likely to be acceptable.


Michael Thayer | VirtualBox engineer
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