[Spice-devel] [protocol RFC 0/2] RANDR support via QXLHead + SpiceHead

[Noel Van Hook]

How far away is a multi-head solution, do you think?
It sounds like most of the work is in the client and the X driver?
Noel

On Mon, May 7, 2012 at 12:28 AM, Alon Levy <alevy at redhat.com> wrote:
> Hi,
>
>  Currently we support multiple monitors by having:
>  single pci = single display channel = single client window
>
>  The RANDR architecture doesn't lend itself to this, but on the other hand it
>  makes it very easy to have an alternative scheme:
>  single pci = single display channel = multiple client windows
>
>  RANDR introduces a concept of a CRTC and an OUTPUT. The CRTC scansout a
>  portion of the framebuffer onto one or more OUTPUTs. I propose having a 1:1 CRTC:OUTPUT correspondence and introducing two new commands, one on PCI and one for the protocol:
>  QXLHead = (id, x, y, width, height)
>  SpiceHead = (id, x, y, width, height)
>
>  1. Guest enables a new monitor:
>  2. Guest pushes QXLHead command to command ring
>  3. Server sends SpiceHead message on the ring's display channel.
>  4. Client creates a window out of [x, y, width, height] scanning out of the primary surface (there is one associated primary with the display channel)
>
> Some other notes:
>  a. To disable a monitor, send (id, 0, 0, 0, 0) (So there remain invalid range of
>  values {(id, x, y, width, height) | max(x, y, width, height)!=0 and min(width,
>  height) = 0})
>  b. Guest keeps track of the head id.
>  c. No idea if this is easy / natural for a WDDM driver, if not we will keep having multiple display channels there, or have to extend the concept of primary to have a number of primary surfaces. Another option is to extend the QXLHead/SpiceHead to have a surface id argument. But I suggest to postpone this to when we actually work on the WDDM driver (unless someone wants to look at it now).
>  d. Improvements from this method are:
>  single vram bar for multiple heads, single ram bar - more efficient memory allocation
>  single display channel means single glz dictionary, single image cache, again more efficient.
>  limit of 4 monitors is lifted (the limit of four display channels remains)
>  implementation for guest is trivial:
>   keep track of enclosing size of primary and resize it as needed
>   issue a QXLHead for each output enabled / disabled (corresponds with crtc since we keep a 1:1 relation in the driver).
>
> I have a proof of concept driver, but needs some work yet. I want to get input on this scheme, it is also very related to application remoting, but I haven't given it thought so far.
>
> Alon Levy (2):
>  qxl_dev: dynamic head support on single display channel
>  protocol: add SPICE_DISPLAY_CAP_HEAD
>
>  spice/protocol.h |    4 ++++
>  spice/qxl_dev.h  |   12 ++++++++++++
>  2 files changed, 16 insertions(+)
>
> --
> 1.7.10.1
>
> _______________________________________________
> Spice-devel mailing list
> Spice-devel at lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/spice-devel



-- 
Noel Van Hook - Intelligraphics, Inc
522 Cooper Ave N
Red Lodge, MT 59068
Noel.Van.Hook at Intelligraphics.com  (425) 770-5561