I have a Lenovo X1 Yoga 2nd generation, with the Intel HD 620 chipset, running Arch Linux, up-to-date with the latest kernel from the Arch repo. It has a built-in HDMI port I'd like to use.
Using the i915 driver, I can see a connected HDMI 4k tv in xrandr. However, the TV invariably reports 'no signal' regardless of the TV (I have tried three of differing models). I have tried telling xrandr to set different resolutions, and changing a few properties, but nothing ever gives me anything besides 'no signal'. There do not appear to be any directly related dmesg errors. If I enable i915.verbose_state_checks=1 then I do get a stream of messages, but I don't see anything obviously wrong, although I don't understand most of it.
In addition, I've found that if I run with nomodeset or i915.modeset=0 and set the EFI to boot using the external display, then the HDMI output will work, but then I am stuck routing everything through the very limited fb drivers.
The laptop additionally provides two USB-C connectors which show up as DP-1 and DP-2. Both of these result in 'No signal' as well, however unlike the HDMI output I get an error in dmesg about
"[ 3049.558501] [drm:intel_dp_start_link_train [i915]] *ERROR* failed to enable link training"
Linux excalibur 5.6.15-arch1-1 #1 SMP PREEMPT Wed, 27 May 2020 23:42:26 +0000 x86_64 GNU/Linux
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