Can't control brightness - iMac 2013

Fedora 33 Workstation works great except for controlling the brightness on my 2013 iMac (iMac14,1). This computer uses the Intel Iris Pro Graphics 5200 as its GPU.

After entering a GNOME session (both Xorg and Wayland), I can move the slider but the brightness doesn’t seem to change. I tried appending several acpi_backlight boot parameters with no luck, but then I noticed that when I suspended the machine and afterwards woke it up the slider would actually control the brightness properly.

Checking the Problem Reporting application shows that xorg-x11-drv-intel crashes after waking the computer from suspension because of “WARNING: CPU: 3 PID: 2350 at drivers/gpu/drm/i915/display/intel_display_power.c:4850 hsw_enable_pc8+0x61e/0x640 [i915] [i915]”.

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