[Bug 199621] iMac 2009, Mobility Radeon HD 4670: black screen on boot

[bugzilla-daemon at bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=199621

Matthew Trescott (matthewtrescott at gmail.com) changed:

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--- Comment #6 from Matthew Trescott (matthewtrescott at gmail.com) ---
Created attachment 276935
  --> https://bugzilla.kernel.org/attachment.cgi?id=276935&action=edit
strace log of xorg when I ran the command that fixes this problem

I have a 21.5-inch Mid-2010 iMac with the same Mobility Radeon HD 4670 GPU. It
also exhibits this problem (the solution in #100301 doesn't work either);
however I can temporarily fix it by running the following command (I had to
type it blindly because it won't work over SSH):

xrandr -d :0 --output eDP-1 --crtc 1

After which everything works well, including backlight control via
/sys/class/backlight/radeon_bl0/brightness. The fix does not persist across
reboots or even across log-out/log-in cycles (I guess the handoff between Xorg
and radeondrmfb triggers some sort of reset and the problem comes back).

I'm on kernel 4.17.2 (Arch Linux). I'm no Linux graphics expert, but I did
capture an strace of all the ioctl calls from Xorg during while running the
above command as well as monitoring sysfs with inotifywait. Nothing relevant
happened in sysfs, but there were a few interesting system calls from when I
ran the command that I've attached.

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