is 4k desktop possible on freebsd-12?

Hi,

I'm trying to get xorg to display 4k. The context is:

FreeBSD 12.0-ALPHA8 r339084 amd64
ports r481640
AMD RX580 GPU
Asus X99 Extreme3 mobo
cpu: intel e5-2699v4
48GB RAM
Samsung UE48JU6410U monitor connected via HDMI

drm-next-kmod-4.11.g20180822
libdrm-2.4.93,1
xf86-video-amdgpu-18.1.0
xf86-video-ati-18.1.0,1
xf86-video-openchrome-0.6.0_3
xf86-video-scfb-0.0.4_7
xf86-video-vesa-2.4.0_2
linux_base-c7-7.4.1708_6 and all its xorg/mesa libs

/var/log/Xorg.0.log has this:

[  3470.966] (II) AMDGPU(0): Printing probed modes for output HDMI-A-0
[  3470.966] (II) AMDGPU(0): Modeline "1920x1080"x60.0  148.50  1920 
2008 2052 2200  1080 1084 1089 1125 +hsync +vsync (67.5 kHz e)
[  3470.966] (II) AMDGPU(0): Modeline "1680x1050"x59.9  119.00  1680 
1728 1760 1840  1050 1053 1059 1080 +hsync -vsync (64.7 kHz e)
[  3470.966] (II) AMDGPU(0): Modeline "1600x900"x60.0  108.00  1600 1624 
1704 1800  900 901 904 1000 +hsync +vsync (60.0 kHz e)

but further along we have this:

[  3474.097] (II) AMDGPU(0): EDID vendor "SAM", prod id 3140
[  3474.097] (II) AMDGPU(0): Using EDID range info for horizontal sync
[  3474.097] (II) AMDGPU(0): Using EDID range info for vertical refresh
[  3474.097] (II) AMDGPU(0): Printing DDC gathered Modelines:
[  3474.098] (II) AMDGPU(0): Modeline "3840x2160"x0.0  297.00  3840 4016 
4104 4400  2160 2168 2178 2250 +hsync +vsync (67.5 kHz eP)
[  3474.098] (II) AMDGPU(0): Modeline "1920x1080"x0.0  148.50  1920 2008 
2052 2200  1080 1084 1089 1125 +hsync +vsync (67.5 kHz e)
[  3474.098] (II) AMDGPU(0): Modeline "800x600"x0.0   40.00  800 840 968 
1056  600 601 605 628 +hsync +vsync (37.9 kHz e)

and

[  3474.211] (II) AMDGPU(0): Printing DDC gathered Modelines:
[  3474.211] (II) AMDGPU(0): Modeline "3840x2160"x0.0  297.00  3840 4016 
4104 4400  2160 2168 2178 2250 +hsync +vsync (67.5 kHz eP)
[  3474.211] (II) AMDGPU(0): Modeline "1920x1080"x0.0  148.50  1920 2008 
2052 2200  1080 1084 1089 1125 +hsync +vsync (67.5 kHz e)
[  3474.211] (II) AMDGPU(0): Modeline "800x600"x0.0   40.00  800 840 968 
1056  600 601 605 628 +hsync +vsync (37.9 kHz e)

so would this indicate the card is 4k capable but the HDMI port on the 
card is not? Or the port on the monitor? Or something else?

thanks,

-- 
J.