Gemini Lake - can't change refresh rate with default EDID and loading of custom EDID fails with eDP

Submitted by aufkrawall @aufkrawall

Assigned to Intel GFX Bugs mailing list

Link to original bug (#111410)

Description

Device is a Trekstor Surfbook A13B notebook with Celeron N4000 (Graphics 600) SoC. It features a 1080p eDP display (without panel self refresh feature).

The display's default EDID offers 59.9xHz and 48Hz for 1080p.
But: When switching to the 48Hz resolution via xrandr, the display continues running with 59.9xHz. Though some applications expect 48Hz then (e.g. mpv), causing bad stutter.
On Windows, changing refresh rate to 48Hz works without issues.

Also, loading a custom EDID or using custom Xorg modelines doesn't help, the display always runs with 59.9xHz and the resolutions/refresh rates of the custom EDID aren't even parsed correctly (only 59.9xHz are offered). Furthermore, the display then only runs with limited brightness level range, causing a washed out look.
On Windows, installing the very same EDID as custom monitor driver works correctly: The resolutions/refresh rates are parsed correctly, it correctly uses full range brightness levels and the display actually switches to the target refresh rates.

Not being able to use different refresh rates is quite annoying, as watching movies etc. is not optimal with 59.9xHz.