22.12.2016 08:07, Daniel Vetter пишет:
On Wed, Dec 21, 2016 at 03:30:04PM +0100, Michael Thayer wrote:
21.12.2016 10:05, Daniel Vetter wrote:
On Tue, Dec 20, 2016 at 11:38:52AM +0100, Michael Thayer wrote:
The suggested X and Y connector properties are intended as a way for drivers
for virtual machine GPUs to provide information about the layout of the
host system windows (or whatever) corresponding to given guest connectors.
The intention is for the guest system to lay out screens in the virtual
desktop in a way which reflects the host layout. Sometimes though the guest
system chooses not to follow those hints, usually due to user requests. In
this case it is useful to be able to pass information back about the actual
layout chosen.
The immediate use case for this is host-to-guest pointer input mapping.
Qemu, VirtualBox and VMWare currently handle this by providing an emulated
graphics tablet device to the guest. libinput defaults, as did X.Org before
it used libinput, to mapping the position information reported by the device
to the smallest rectangle enclosing the screen layout. Knowing that layout
lets the hypervisor send the right position information through the input
device.
Signed-off-by: Michael Thayer <michael.thayer@xxxxxxxxxx>
---
Follow-up to thread "Passing multi-screen layout to KMS driver". In that
thread, Gerd suggested an alternative way of solving the use case, namely
emulating one input device per virtual screen, touchscreen-style. My reasons
for prefering this approach is that it is relatively uninvasive, and closer
to the way things are done now without (in my opinion) being ugly; and that
automatic touchscreen input to screen mapping is still not a solved problem.
I think that both are valid though.
Both approaches require changes to the hypervisor and virtual hardware, and
to user-space consumers which would use the interface. I have checked the
mutter source and believe that the change required to support the interface
as implemented here would be minimal and intend to submit a patch if this
change is accepted. I think that the virtual hardware changes are likely to
be less invasive with this approach than with the other. This change will
though also require small drm driver changes once the virtual hardware has
been adjusted; currently to the qxl driver and to the out-of-tree vboxvideo
driver. It would certainly be nice to have in virtio-gpu.
Makes sense I think, but for merging we need:
- some driver to implement
This is where it starts getting tricky. vboxvideo is out of tree. In
theory I could look at getting it merged, but that needs time I am rather
short of (I am the only person maintaining that driver and it is just one of
my responsibilities; and there are some bits there that are probably too
ugly to merge as is). I don't think I am really the person to be doing this
for qxl/virtio-gpu as that required adding the support to qemu too. I think
that they really should have it, but I would rather not be the one adding
it. So would our out-of-tree driver be good enough?
I don't see the point in merging core code for out-of-tree drivers. If
it's out-of-tree you can just add this locally (by adding the property).
Has ofc the risk of uapi breakage or not upstream opting for a slightly
different flavour, but that's the price for not being upstream.
Evil question: I just can't see myself getting it upstream in the near
future for lack of time. How much success am I likely to have asking
for volunteers? (I do not see a reason why other people should have
more time than I do, but you never know.) Obviously I would continue
committing to it and would probably switch to keeping our out-of-tree
driver in sync with the in-kernel one. For interest, the files are
mainly in these places, and the other referenced include files are
mainly compatibility layer things which would probably want eliminating:
https://www.virtualbox.org/browser/vbox/trunk/src/VBox/Additions/linux/drm
https://www.virtualbox.org/browser/vbox/trunk/src/VBox/Additions/common/VBoxVideo
https://www.virtualbox.org/browser/vbox/trunk/src/VBox/GuestHost/HGSMI
https://www.virtualbox.org/browser/vbox/trunk/include/VBox/VBoxVideo.h
https://www.virtualbox.org/browser/vbox/trunk/include/VBox/VBoxVideoGuest.h
https://www.virtualbox.org/browser/vbox/trunk/include/VBox/HGSMI
Otherwise, yes, I could try implementing the interface out-of-tree, and
see if the GNOME Shell people were still receptive to it (no point in
doing it if they are not). Hopefully if GNOME Shell used it other
virtualisation drivers would pick it up too.
Regards
Michael
-Daniel
--
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