DisplayPort over USB-Type C Connector Not Recognised on Intel NUC8i5BEK (Gen 9, CoffeeLake)
Submitted by Geoffrey Allott
Assigned to Intel GFX Bugs mailing list
Link to original bug (#112072)
Description
I am running linux kernel 5.3.1 on an Intel NUC8i5BEK which has CoffeeLake graphics (Intel® Iris® Plus Graphics 655).
The device has two graphics output ports, 1 HDMI and 1 USB Type-C. The kernel reports 3 connectors; port A appears to be for embedded DisplayPort which is reported disconnected (there is a note "Haswell uses DDI functions to detect digital outputs. On SKL pre-D0 the strap isn't connected, so we assume it's there.").
I've connected an ASUS ROG PG278Q Monitor to the USB Type-C port using a Type-C to DisplayPort cable, but no video modes are reported except for the default VGA ones, meaning I'm stuck at a resolution of 1024x768. (The monitor supports 2560x1440@144). The video output does work, though.
I have noticed that the function bool intel_phy_is_tc(struct drm_i915_private *dev_priv, enum phy phy)
will always return false
for this particular GPU (which is GEN 9).
In static int intel_dp_get_modes(struct drm_connector *connector)
for DP-2 (the only connected connector) there is no EDID detected, it is not eDP and there is no fixed mode; so get_modes adds no modes.
I should note that this problem occurs both on my custom kernel and on the latest Arch Linux ISO and the latest Ubuntu ISO. The Intel UEFI-BIOS recognises the monitor's native resolution just fine.
Here's my kernel config:
https://pastebin.com/hStMFVfE
Here's a kernel log with drm logging enabled:
https://pastebin.com/VNhZGJPu