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

[Yonit Halperin]

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.


>    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(+)
>