I have a discrete AMD card (Tonga) using amdgpu and an iGPU (Skylake/HD530)
using the intel driver.

I enabled DRI3 on both devices, but xrandr only shows the outputs/monitors of
the AMD card.

When I use "xrandr --setprovideroutputsource 1 0" everything is still fine,
xrandr shows now all outputs/monitors.

When I try to enable the monitor connected to the iGPU via "xrandr --output
HDMI3 --auto" the x-server segfaults with the following backtrace:

#0  0x00007fdffdd2334d in glamor_block_handler () from
/usr/lib64/xorg/modules/libglamoregl.so
#1  0x00007fe00d639f8b in amdgpu_glamor_flush () from
/usr/lib64/xorg/modules/drivers/amdgpu_drv.so
#2  0x00007fe00d62df23 in redisplay_dirty () from
/usr/lib64/xorg/modules/drivers/amdgpu_drv.so
#3  0x00007fe00d62f728 in AMDGPUBlockHandler_KMS () from
/usr/lib64/xorg/modules/drivers/amdgpu_drv.so
#4  0x000000000043a27f in BlockHandler ()
#5  0x0000000000587ac3 in WaitForSomething ()

Here are further details, including the Xorg.log and the used configs:
https://gist.github.com/EoD/c1c4f2b4afde2d0523e9ea8bb1567452