xrandr does not correctly switch display refresh rates, but pretends it did

Submitted by Nicolas Frattaroli

Assigned to Intel GFX Bugs mailing list

Link to original bug (#107064)

Description

Created attachment 140380
xrandr fails to set the mode correctly, but claims it is in 48 Hz mode

Telling xrandr to switch to 48 Hz mode with xrandr --rate 48 makes the screen go black for a moment, and xrandr says it is now running at 48 Hz, but applications which wait for vsync still swap roughly 60 times per second.

The display is connected to eDP.

$ uname -r
4.18.0-rc2-drm-tip+
$ uname -m
x86_64

See the attachment for a log of me running xrandr to show the current state, then switching the output refresh rate, then running xrandr to show it again, and then running glxgears to show that it's still swapping at roughly 60 Hz.

Attachment 140380, "xrandr fails to set the mode correctly, but claims it is in 48 Hz mode":
log.txt