CFL is trying to use eDP as display even it is not connected and then looses it. It seems to be a race condition that when eDP is lost and external display is not yet found lightdm tries to start. Therefore it fails to boot up. Delayed lightdm start works because external display is recognized when lightdm is started after 10 seconds
With only external display attached X fails to start With eDP connected it can start X without issue
Created attachment 134813 [details] verbose dmesg from LAB-CFL-S
The VBT says we have eDP, so we try it. Turns out we can't talk to it, so we don't register it after all. Doesn't even seem to take all that long to figure this out. I don't see why eDP should be an issue here.
There are two issues in this bug. One is that the VBT (BIOS CNLSFWX1.R00.X095.A04.17072407838) is unable to detect lspcon (Megachip MCDP2800) and therefore it is not getting initialized. The effect of this is that DP doesn't light up. If you force lspcon in kernel the DP lights up. The second problem is the X. On a bootup X falls back to SW rendering.
Switching to BIOS CNLSFWR1.R00.X104.B11.1710091318 has lspcon supported so the i915 driver can initialize and use Megachip MCDP2800 DP-to-HDMI converter properly. Second problem with was fixed by updating mesa.
With BIOS CNLSFWR1.R00.X104.B11.1710091318 perf team CFL now boots with drm_intel kernel from HDMI port with HW accelerated graphics.
So this can be resolved?
CFL on CI system works perfectly with upgraded BIOS. Perf team CFL does not show boot menu with HDMI connection only. It does boot to drm_intel desktop. My vote goes for resolving this bug.
With delay workaround it works and it seems to work with new HW with correct BIOS. marking as resolved.
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