[Bug 108997] RX460: Some Resolution-Refresh Combinations Unavailable when Connected via DisplayPort

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=108997

            Bug ID: 108997
           Summary: RX460: Some Resolution-Refresh Combinations
                    Unavailable when Connected via DisplayPort
           Product: DRI
           Version: unspecified
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/AMDgpu
          Assignee: dri-devel at lists.freedesktop.org
          Reporter: jeffbai at aosc.io

- 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

--------

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

--------

While connecting my XFX Radeon RX460 Slim to a Samsung 900SL CRT monitor via a
DisplayPort to VGA converter cable, 1600x1200 at 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 at 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 at NetVista [ / ] $ xrandr --newmode "1600x1200_76.00"  207.50  1600
1720 1888 2176  1200 1203 1207 1256 -hsync +vsync

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

mingcongbai at 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.

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