Haswell Brightness Fix:
DSDT Patches from here:
https://github.com/RehabMan/Laptop-DSDT-Patch
Apply:
"Rename GFX0 to IGPU"
"Brightness Fix (Haswell)"
- rename patch must be done first and to all DSDT/SSDT that contain references to GFX0 that you're including in your final SSDT set
- Brightness patch must be done to the DSDT or SSDT that contains the definition for Device GFX0 (search for 'Device (GFX0)'
- Place DSDT and SSDT (if necessary) into a place where the bootloader will load them. For Clover, EFI/CLOVER/ACPI/patched (DSDT.aml, SSDT-x.aml where 'x' is a number). For Chameleon, /Extra/ssdt.aml, /Exra/ssdt-1.aml, /Extra/ssdt-2.aml, etc.
Install:
https://github.com/RehabMan/OS-X-ACPI-Backlight
Which ig-platform-id are you using? HDMI may require framebuffer edits, although I say it works flawlessly on my HD4400-based Lenovo U430 using vanilla kexts...
Check your codec dump to see if the nodes have an EAPD amp. If they do, you need CodecCommander.kext (customized for your codec nodes).
I would need to see your unpatched DSDT and the patches you used, or patched DSDT. Given the snippet above, SMDX is, in fact, at offset 4. You must make sure you place RECB in the correct place. And, of course, any writes to SMD0 must be handled via WECB. There could be additional multi-byte EC fields in the DSDT as well that you have not shown above.