[coreboot-gerrit] Change in coreboot[master]: mb/clevo/kbl-u: Install Intel VGA INT15 handler

[Benjamin Doron (Code Review)]

Benjamin Doron has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/43852 )

Change subject: mb/clevo/kbl-u: Install Intel VGA INT15 handler
......................................................................

Patch Set 5:
> Patch Set 1:
>
> The VBIOS Option ROM does not light up the screen, and TianoCore is also not showing anything.
> PCI: 00:02.0 init
> FMAP: area COREBOOT found @ 350200 (4914688 bytes)
> CBFS: Locating 'vbt.bin'
> CBFS: Found @ offset 705c0 size 4a3
> Found a VBT of 6144 bytes after decompression
> GMA: Found VBT in CBFS
> GMA: Found valid VBT in CBFS
> FMAP: area COREBOOT found @ 350200 (4914688 bytes)
> CBFS: Locating 'pci8086,5916.rom'
> CBFS: Found @ offset 102e00 size 10000
> In CBFS, ROM address for PCI: 00:02.0 = 0xffc53048
> Copying VGA ROM Image from 0xffc53048 to 0xc0000, 0x10000 bytes
> Calling Option ROM...
> intel_vga_int15_handler: AX=5f34 BX=0190 CX=0002 DX=03da
> intel_vga_int15_handler: AX=5f51 BX=c000 CX=0000 DX=03da
> intel_vga_int15_handler: AX=5f40 BX=0000 CX=0004 DX=0008
> DISPLAY=0
> intel_vga_int15_handler: AX=5f52 BX=400a CX=000f DX=0008
> Unknown INT15 function 5f52!
> int15 call returned error.                  
> intel_vga_int15_handler: AX=5f49 BX=19ff CX=0000 DX=1dcc
> Unknown INT15 function 5f49!               
> int15 call returned error.
> intel_vga_int15_handler: AX=5f49 BX=0050 CX=0300 DX=0040
> Unknown INT15 function 5f49!
> int15 call returned error.
> intel_vga_int15_handler: AX=5f14 BX=078f CX=0002 DX=0008
> Unknown INT15 function 5f14!
> int15 call returned error.
> intel_vga_int15_handler: AX=5f35 BX=c000 CX=0002 DX=03da
> ... Option ROM returned.
> VGA Option ROM was run 
> PCI: 00:02.0 init finished in 326 msecs

According to the BSF script file for the SKL/KBL/CFL/AML VGABIOS, these are the int15 functions called that coreboot does not support:
5f52h: Hook to get Panel Color Depth from Setup (Mobile only)
5f49h: Hook to get the backlight inverter type, polarity and initial brightness
5f14h: Get Miscellaneous Status (Mobile only)

The information provided by the first two should be available in the VBT inside the VGABIOS. You could try using the Intel BMP (Binary Modification Program) to disable these hooks. The last hook is apparently required for DisplayPort Redriver suppoort.