Display port over USB-C not working - PBP

I've tried connecting an external display with two different usb-c to dp cables. The dmesg output is the same for both.

When plugging in:

cdn-dp fec00000.dp: [drm:cdn_dp_pd_event_work [rockchipdrm]] Not connected. Disabling cdn
cdn-dp fec00000.dp: [drm:cdn_dp_pd_event_work [rockchipdrm]] Connected, not enabled. Enabling cdn
cdn-dp fec00000.dp: [drm:cdn_dp_check_sink_connection [rockchipdrm]] *ERROR* Get sink capability timed out
cdn-dp fec00000.dp: [drm:cdn_dp_pd_event_work [rockchipdrm]] *ERROR* Enable dp failed -19

When unplugging:

cdn-dp fec00000.dp: [drm:cdn_dp_pd_event_work [rockchipdrm]] Not connected. Disabling cdn
cdn-dp fec00000.dp: [drm:cdn_dp_pd_event_work [rockchipdrm]] Not connected. Disabling cdn

Using the minimal edition from manjaro-arm-installer.

$ uname -a
Linux kraken-arm 5.7.4-1-MANJARO-ARM #1 SMP Thu Jun 18 17:08:35 CEST 2020 aarch64 GNU/Linux

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