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

[Alon Levy]

On Tue, May 08, 2012 at 10:30:17AM +0300, Yonit Halperin wrote:
> On 05/07/2012 09:28 AM, Alon Levy 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.
> Small comment: we already have one glz dictionary and one image cache, and
> they are shared among the different display channels.
> 
My mistake, thanks for the correction.

> 
> >   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(+)
> >
>