Ilija Hadzic's Virtual CRTCs feature discuss

Derek derek0883 at
Mon Aug 25 12:02:09 PDT 2014

Hi, Daniel
Thanks for your response!
Talking about v4l's virtual gpu driver?  Could you please tell some more
informations. is this driver in
I want to take a look this driver. but I can't find it in their git
repository. Or is there any introduction post related this driver? Thanks.

Best wishes

On Mon, Aug 25, 2014 at 6:12 AM, Daniel Vetter <daniel at> wrote:

> On Mon, Aug 18, 2014 at 03:35:16PM -0700, Derek wrote:
> > Hi every one
> > I'm currently working on VirtualMonitor in my leisure time. It allows you
> > to use compute/tablet/smartphone as a second monitor for your primary
> > computer. please refer to for more
> > information. Currently I have released very basic version for
> > windows2000-windows7 to demonstrate the project is feasible. When I was
> > trying to make a further step on windows, I realized it is difficult for
> an
> > individual, as it is not open source and also without technical support
> > from Microsoft.
> >
> > Then I want to move to linux, and I found Ilija Hadzic's post about
> Virtual
> > CRTCs. his post is here:
> >
> > In his implementation, GPU driver can create arbitrary number of CRTCs
> > (configurable by user) instead of only those CRTCs that represent real
> > hardware.
> > It is very useful not only for VirtualMonitor, but also
> > VNC/Virtualization/USB display etc. based on this implementation those
> > application will be able to take full advantage of the physical graphic
> > card(3D acceleration).
> >
> > I want raise Ilijia's original question agian, if anybody in this
> community
> > think Virtual CRTCs is useful, and willing to work together to make a
> > further progress.
> > My thought is if can implement a driver independent layer between dri and
> > vendor specific GPU driver, with some general API. maybe implement this
> > based one vendor related GPU first? e.g. based on Ilijia's implementation
> > for Radeon as a daemon?
> >
> > GPU driver is not my expertise, If some expert from this community think
> > this feature is interesting, and willing to initiate a project for this
> > feature, that will be great. Then people can work and discuss together.
> >
> > Any comments regarding to Virtual CRTC or VirtualMonitor are very
> welcome.
> > Thanks.
> I think the concept is overall sound (haven't looked at the old patches in
> detail).For the actual implementation I think a separate virtual drm
> driver is now
> the better approach, since with dma-buf and soon native fence support we
> can do this now properly.
> And especially now that we have multi-gpu support in X it should integrate
> almost seamlessly into X (and other display managers with multi-gpu
> support). Instead of requering special support in all drivers.
> Another thing for which iirc no one ever proposed a decent solution is
> synchronization to consumers of the frontbuffers for virtual gpus. So I
> guess the driver-private ioctl interface to make that magic work will be
> key.
> A (configurable) virtual gpu should also be really useful for automated
> testing, e.g. of hot-plug and unplug (both drm core and userspace). The
> v4l folks have such a driver (recently massively revamped for 3.18) and it
> looks extremely useful.
> For the configuration interface I guess a few simple module options to get
> started should be enough, eventually we can switch to configfs (or
> similar) to be able to configure and create/destroy virtual gpus at
> runtime.
> Just my random thoughts, probably good to kickstart the discussion with
> some quick patches and chat with people on #dri-devel on freenode irc.
> Cheers, Daniel
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> +41 (0) 79 365 57 48 -
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