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RX460: Some Resolution-Refresh Combinations Unavailable when Connected via DisplayPort

Submitted by Mingcong Bai

Assigned to Default DRI bug account

Link to original bug (#108997)

Description

  • Xorg Server version: 1.20.3
  • XRandR version: 1.5.0
  • Xf86-Video-AMDGPU version: 18.0.1
  • Kernel parameters: root=UUID=dfd3d587-145e-4c01-af04-a3e24c59e95c rw quiet rw rd.auto rd.auto=1 splash vfio-pci.ids=10de:1c03,1022:145f,1022:1457 modprobe.blacklist=nouveau iommu=pt amd_iommu=on kvm-amd.avic=1 kvm-amd.nested=1 clocksource=tsc kvm.ignore_msrs=1 pcie_acs_override=multifunction rd.driver.pre=vfio-pci video=efifb:off

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Xorg.conf:

Section "Device"
Identifier "Device 0"
Driver "amdgpu"
VendorName "Advanced Micro Devices, Inc."
BusID "PCI:34:0:0"
Option "IgnoreEDID" "true"
Option "UseEDID" "false"
EndSection

Section "Monitor"
Identifier "Monitor 0"
VendorName "SAMSUNG"
ModelName "900SL"
Option "UseEDID" "false"
Option "UseEDIDFreqs" "false"
Option "DDC" "false"
HorizSync 30.0 - 96.0
VertRefresh 50.0 - 100.0
Modeline "1600x1200_76.00" 207.50 1600 1720 1888 2176 1200 1203 1207 1256 -hsync +vsync
Option "PreferredMode" "1600x1200_76.00"
EndSection

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While connecting my XFX Radeon RX460 Slim to a Samsung 900SL CRT monitor via a DisplayPort to VGA converter cable, 1600x1200@76Hz is not available, despite the factory specs...

1600 x 1200 / 76 Hz
1600 x 1200 / 70 Hz
1600 x 1200 / 65 Hz
1280 x 1024 / 89 Hz
1024 x 768 / 119 Hz
800 x 600 / 152 Hz
640 x 480 / 160 Hz

When attempting to create a new custom mode...

mingcongbai@NetVista [ / ] $ cvt 1600 1200 76
# 1600x1200 75.92 Hz (CVT) hsync: 95.36 kHz; pclk: 207.50 MHz
Modeline "1600x1200_76.00" 207.50 1600 1720 1888 2176 1200 1203 1207 1256 -hsync +vsync

mingcongbai@NetVista [ / ] $ xrandr --newmode "1600x1200_76.00" 207.50 1600 1720 1888 2176 1200 1203 1207 1256 -hsync +vsync

mingcongbai@NetVista [ / ] $ xrandr --addmode DisplayPort-0 "1600x1200_76.00"

mingcongbai@NetVista [ / ] $ xrandr --output DisplayPort-0 --mode "1600x1200_76.00"
xrandr: Configure crtc 0 failed

I have an NVIDIA GeForce GTX1060 passed through to a Windows 10 VM, connected via a DisplayPort to VGA, and VGA to BNC 5-pin connector, in this case, 1600x1200 is available and displays a correct image.

I have also tried to connect the RX460 with the DP-VGA-BNC cable, which yielded the same result.