[Bug 110217] RX580: screen turns black or flickers until forced reconfiguration

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=110217

            Bug ID: 110217
           Summary: RX580: screen turns black or flickers until forced
                    reconfiguration
           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: numzer0 at yandex.ru

Created attachment 143754
  --> https://bugs.freedesktop.org/attachment.cgi?id=143754&action=edit
dmesg output

I have a Radeon RX560 and VGA monitor (with broken EDID) connected via a cheap
HDMI-to-VGA converter (with its own broken EDID).

The system starts up normally. During boot up, it should change display
resolution as specified in the kernel command line (`video=1280x1024-32 at 75`,
monitor native). Screen turns black instead, and resolution remains unchanged.
But after I plug HDMI out and in, the monitor gets new resolution and shows
console login prompt, as expected. (X isn’t configured to start at bootup).

Then, when I `startx`, it chooses the same resolution but wrong frequency (85
Hz, too much for my monitor). That’s probably due to converter supplying the
EDID. After I run `xrandr --rate 75`, it switches to the correct mode.

I wouldn’t even mention such small nuisance, but if I specify exactly the same
mode (as reported by `xrandr --verbose`) explicitly (as a `Modeline`), it works
but flickers, despite the `TearFree` option enabled. Moreover, when the monitor
is turned off and then on, it wakes up in the same mode *but flickers.*
Changing mode back and forth (`xrandr --output HDMI-A-0 --preferred ; xrandr
--rate 75`) helps.

I usually have `compton` running. Without it, flicker is tolerable but still
present.

OS: Arch Linux
Kernel: Linux 5.0.1-arch1-1-ARCH
X driver: xf86-video-amdgpu 19.0.0-1

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