I'm trying to use coreboot for gigabyte ga-ma785gmt-ud2h 

but booting sequence hangs during pci enumeration in ramstage.

I found that reading pci configuration space of on-board VGA (RADEON HD 4200) 

is source of the problem. 

I tried to modify compile configuration in order to disable mmconf and use ported i/o (in, out instructions)

but still the coreboot fails at the same location. (pci enumeration step for the onboard VGA)

My coreboot stops during pci_conf1_read_config32 call. (at 'return inl(0xCFC);' )

I also tried to extract vga bios and embed it into coreboot using "Add a VGA BIOS image" option,

but it didn't make any changes.

How can i resolve this situation? I have no idea. Any comments or helps will be really appreciated for me.

I have attached serial port debug messages.

Followings are the result of lspci command after the normal BIOS booting.

ilios@ilios-GA-MA785GMT-UD2H:~$ lspci

00:00.0 Host bridge: Advanced Micro Devices, Inc. [AMD] RS880 Host Bridge

00:01.0 PCI bridge: Advanced Micro Devices, Inc. [AMD] RS780/RS880 PCI to PCI bridge (int gfx)

00:0a.0 PCI bridge: Advanced Micro Devices, Inc. [AMD] RS780/RS880 PCI to PCI bridge (PCIE port 5)

00:11.0 SATA controller: Advanced Micro Devices, Inc. [AMD/ATI] SB7x0/SB8x0/SB9x0 SATA Controller [IDE mode]

00:12.0 USB controller: Advanced Micro Devices, Inc. [AMD/ATI] SB7x0/SB8x0/SB9x0 USB OHCI0 Controller

00:12.1 USB controller: Advanced Micro Devices, Inc. [AMD/ATI] SB7x0 USB OHCI1 Controller

00:12.2 USB controller: Advanced Micro Devices, Inc. [AMD/ATI] SB7x0/SB8x0/SB9x0 USB EHCI Controller

00:13.0 USB controller: Advanced Micro Devices, Inc. [AMD/ATI] SB7x0/SB8x0/SB9x0 USB OHCI0 Controller

00:13.1 USB controller: Advanced Micro Devices, Inc. [AMD/ATI] SB7x0 USB OHCI1 Controller

00:13.2 USB controller: Advanced Micro Devices, Inc. [AMD/ATI] SB7x0/SB8x0/SB9x0 USB EHCI Controller

00:14.0 SMBus: Advanced Micro Devices, Inc. [AMD/ATI] SBx00 SMBus Controller (rev 3c)

00:14.1 IDE interface: Advanced Micro Devices, Inc. [AMD/ATI] SB7x0/SB8x0/SB9x0 IDE Controller

00:14.2 Audio device: Advanced Micro Devices, Inc. [AMD/ATI] SBx00 Azalia (Intel HDA)

00:14.3 ISA bridge: Advanced Micro Devices, Inc. [AMD/ATI] SB7x0/SB8x0/SB9x0 LPC host controller

00:14.4 PCI bridge: Advanced Micro Devices, Inc. [AMD/ATI] SBx00 PCI to PCI Bridge

00:14.5 USB controller: Advanced Micro Devices, Inc. [AMD/ATI] SB7x0/SB8x0/SB9x0 USB OHCI2 Controller

00:18.0 Host bridge: Advanced Micro Devices, Inc. [AMD] Family 10h Processor HyperTransport Configuration

00:18.1 Host bridge: Advanced Micro Devices, Inc. [AMD] Family 10h Processor Address Map

00:18.2 Host bridge: Advanced Micro Devices, Inc. [AMD] Family 10h Processor DRAM Controller

00:18.3 Host bridge: Advanced Micro Devices, Inc. [AMD] Family 10h Processor Miscellaneous Control

00:18.4 Host bridge: Advanced Micro Devices, Inc. [AMD] Family 10h Processor Link Control

01:05.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] RS880 [Radeon HD 4200]

01:05.1 Audio device: Advanced Micro Devices, Inc. [AMD/ATI] RS880 HDMI Audio [Radeon HD 4200 Series]

02:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller (rev 02)

03:0e.0 FireWire (IEEE 1394): Texas Instruments TSB43AB23 IEEE-1394a-2000 Controller (PHY/Link)

ilios@ilios-GA-MA785GMT-UD2H:~$