sna: Allow user specification of number of VirtualHeads

Previously, we instantiated a fake output in case we had a machine with
no output. (For certain server-class products.) The Bumblee project were
also doing something very similar in order to fake an extended desktop
on the Intel igfx and copy portions onto a discrete GPU. (The preferred
method for doing this upstream is through the use of PRIME). As the code
is very similar, we can support both use-cases simultaneously.

This adds the option:

Section "Device"
  Driver "intel"
  Option "VirtualHeads" "<count>"
EndSection

to allow the user to specify an additional set of fake outputs, which
can then be controlled using xrandr.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

1 files changed, 12 insertions, 0 deletions

diff --git a/man/intel.man b/man/intel.man
index 9e19687b..0a265114 100644
--- a/man/intel.man
+++ b/man/intel.man
@@ -261,6 +261,18 @@ applications when monitors are connected or disconnected.
 .IP
 Default: enabled.
 .TP
+.BI "Option \*qVirtualheads\*q \*q" integer \*q
+This option controls specifies the number of fake outputs to create in
+addition to the normal outputs detected on your hardware. These outputs
+cannot be assigned to the regular displays attached to the GPU, but do
+otherwise act as any other xrandr output and share a portion of the
+regular framebuffer. One use case for these extra heads is for extending
+your desktop onto a discrete GPU using the Bumblebee project. However,
+the recommendation here is to use PRIME instead to create a single
+Xserver that can addresses and coordinate between multiple GPUs.
+.IP
+Default: 0
+.TP
 .BI "Option \*qZaphodHeads\*q \*q" string \*q
 .IP
 Specify the randr output(s) to use with zaphod mode for a particular driver