Arch Linux

joonatoona

Member

Registered: 2018-08-28

Posts: 1

Website

DisplayPort chaining on Kernel 4.18

Chained DisplayPort monitors no longer work after upgrading the kernel to 4.18.
Display works until modesetting occurs, then switches to "no signal".
Display still shows up correctly in `xrandr`, unplugging and replugging has no effect.

Everything works perfectly on 4.17.14

Also tested on an RX550 with the same results.

$ glxinfo | grep 'renderer string'

OpenGL renderer string: AMD Radeon (TM) RX 480 Graphics (POLARIS10, DRM 3.26.0, 4.18.5-arch1-1-ARCH, LLVM 6.0.1)

$ uname -a

Linux joonabox 4.18.5-arch1-1-ARCH #1 SMP PREEMPT Fri Aug 24 12:48:58 UTC 2018 x86_64 GNU/Linux

$ dmesg | grep amdgpu

[    0.000000] Command line: BOOT_IMAGE=/vmlinuz-linux root=/dev/mapper/joonabox-root rw quiet cryptdevice=UUID=7d263eca-dfd6-40f5-9078-b34c83783355:cryptlvm root=/dev/mapper/joonabox-root amdgpu.dc=1
[    0.000000] Kernel command line: BOOT_IMAGE=/vmlinuz-linux root=/dev/mapper/joonabox-root rw quiet cryptdevice=UUID=7d263eca-dfd6-40f5-9078-b34c83783355:cryptlvm root=/dev/mapper/joonabox-root amdgpu.dc=1
[   10.024129] [drm] amdgpu kernel modesetting enabled.
[   10.035563] fb: switching to amdgpudrmfb from EFI VGA
[   10.036023] amdgpu 0000:1c:00.0: Invalid PCI ROM header signature: expecting 0xaa55, got 0xffff
[   10.036703] amdgpu 0000:1c:00.0: VRAM: 8192M 0x000000F400000000 - 0x000000F5FFFFFFFF (8192M used)
[   10.036705] amdgpu 0000:1c:00.0: GTT: 256M 0x0000000000000000 - 0x000000000FFFFFFF
[   10.036805] [drm] amdgpu: 8192M of VRAM memory ready
[   10.036806] [drm] amdgpu: 8192M of GTT memory ready.
[   10.295447] [drm] Initialized amdgpu 3.26.0 20150101 for 0000:1c:00.0 on minor 0
[   10.820822] fbcon: amdgpudrmfb (fb0) is primary device
[   11.703813] amdgpu 0000:1c:00.0: fb0: amdgpudrmfb frame buffer device

$ xrandr

Screen 0: minimum 320 x 200, current 6000 x 1440, maximum 16384 x 16384
DisplayPort-2 connected primary 3440x1440+2560+0 (normal left inverted right x axis y axis) 800mm x 335mm
   3440x1440     74.92*+  59.94  
DisplayPort-3 connected 2560x1440+0+0 (normal left inverted right x axis y axis) 597mm x 336mm
   2560x1440     59.95*+