Lenovo X1C5 : DP (or HDMI) working but can't get 4K on Sequoia 15.6.1

[jamieakers]

Had a good search, tried many things but cannot get 4K on my Lenovo X1 Carbon Gen 5 (Kaby Lake, Intel HD Graphics 620 ... NOT UHD Graphics 620).  Setup using guide here: https://github.com/anathonous/X1C5-Hackintosh-OpenCore-MacOSX/ with my only changes being to use Heliport and itlwm.kext, and upgrading to latest versions of WhateverGreen.kext and AppleALC.kext. If it makes any difference I'm using a Dell U3219Q connected over USB-C (DP alt-mode) and it's recognised and working at 1440p, USB devices connected to the monitor also work fine (the USB isn't hotplug, not fussed about this.  Audio also doesn't work but again not fussed).

 

Booting from an Ubuntu USB stick and I get 4K - ruling out any issues with the cable or hardware.  DVMT is also set at 256MB in BIOS so I don't think there's an issue there.

 

Things I have tried...

 

- enable-hdmi20 on and off in config.plist.  No effect.

- manually specifying the port as being DP in config.plist with framebuffer-con2-type (con1 is the internal panel).  Black screen trying this.

- a variety of AAPL,ig-platform-id taken from the WEG guide.  No effect.

- igfxmpc in boot-args.  No effect.

- igfxtypec (just in case) in boot-args.  No effect.

 

I've also validated the EDID reported to macOS is correct (checked using IORegistryExplorer) in terms of the supported resolutions.

 

All help gratefully received, thank you!  I'd prefer to get it working over USB-C but if it has to be HDMI so be it.

config.plist.zip

[Hervé]

You're highly unlikely to obtain 4K out of macOS with your current framebuffer patches:

 

Indeed, these apply the usual video memory patches required when Intel DVMT is limited to 32MB. If, as I understood, you've set DVMT to 256MB in BIOS, then you can get rid of your fbmem + stolenmem patches. These are not compatible with 4K operation which usually requires DVMT to be set at a minimum of 64MB.

 

See here: https://osxlatitude.com/forums/topic/17804-dvmtstolenmemfbmemcursormem-why-do-we-patch-these-for-broadwell-and-later

 

I therefore recommend you remove/comment out your fbmem and stolenmem patches. In the same respect, you're highly unlikely to require to set VRAM, i.e. unifiedmem, to 2GB.

[jamieakers]

Thanks for looking at this and getting back to me so quickly!  Tried booting without fbmem + stolenmem but KP and refuses to boot.  Reinstating stolenmem gets the machine to boot without issue.  As using OC 0.9.5 at the moment switched to the debug version per Dortania's instructions.  Making me wonder whether the 256MB setting in BIOS does set DVMT.  It's labelled "Total Graphics Memory" but if there's some way to check please let me know - I couldn't find an obvious way from searching.

 

Attached the produced OpenCore logs.  If any other files would be handy to investigate please do let me know.

opencore-2025-09-30-193108.txt.zip