[PATCH] drm: remove immutable flag from suggested X/Y connector properties

[Michael Thayer]

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 at oracle.com>
>>>> ---
>>>> 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
>

-- 
Michael Thayer | VirtualBox engineer
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