So... how to use it?
Xorg 1.15.1 says:
[ 78.577] Initializing built-in extension DRI3
[ 78.630] (II) Loading sub module "dri3"
[ 78.630] (II) LoadModule: "dri3"
[ 78.631] (WW) Warning, couldn't open module dri3
[ 78.631] (II) UnloadModule: "dri3"
[ 78.631] (II) Unloading dri3
[ 78.631] (EE) intel: Failed to load module "dri3" (module does not exist, 0)
xf86-video-intel 2.99.911 will be compiled with:
Xorg Video ABI version: 15.0
Acceleration backends: *sna uxa
Additional debugging support? none
Support for Kernel Mode Setting? yes
Support for legacy User Mode Setting (for i810)? yes
Support for Direct Rendering Infrastructure: DRI1 DRI2 DRI3 Present
Support for Xv motion compensation (XvMC and libXvMC): yes
Build additional tools and utilities? xf86-video-intel-backlight-helper intel-virtual-output