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= VGA initialization in coreboot v2 =
== VGA initialization in coreboot ==


== General ==
Since coreboot v4 you can configure VGA initialization in Kconfig. For older versions of coreboot check the history of this page.


You need to enable two CONFIG options in your Mainboard Option.lb
First do:


<source lang="bash">
<source lang="bash">
#VGA Console
$ make menuconfig
option CONFIG_CONSOLE_VGA=1
option CONFIG_PCI_ROM_RUN=1
</source>
</source>


'''CONFIG_PCI_ROM_RUN''' will use the embedded x86 emulator to run the BIOS image in the expansion ROM of a PCI device.
Then go
'''CONFIG_CONSOLE_VGA''' will redirect console messages to the VGA screen once VGA card is initialized.
    Chipset  --->
      [*] Setup bridges on path to VGA adapter
      [*] Run VGA option ROMs
      Option ROM execution type (Native mode)  --->


For add-on (PCI/PCIe/PCI-X/AGP) VGA cards, you don't have to do anything else besides these two CONFIG options.
Alternatively you can choose the "Secure mode" to run the VGA option rom in a contained environment.
If your mainboard has an on-board VGA chip and you insert another VGA add-on card, the add-on
VGA card will be used instead of the on-board VGA chip.


== Onboard Video ==
If you have no on-board graphics, you are done configuring coreboot at this point. You may exit configuration, and run make to get your VGA enabled coreboot image.


If you want to use the onboard VGA chip, you have to add the following options in addition to the CONFIG options described above.
=== On-board Video Devices ===


=== Mainboard Configuration ===
If you run coreboot on a system with on-board graphics, you have to embed a VGA  on the top level, enter the file name of your option rom and the PCI ID of the associated graphics device in the form <vendor_id>,<device_id>:


1. In the mainboard Config.lb (./src/mainboard/<mfg>/<board>/Config.lb) You need to specify the device number for your onboard VGA and the address that the video bios will show up at in the system.
    VGA BIOS  --->
    [*] Add a VGA BIOS image
    (oprom-0.rom) VGA BIOS path and filename
    (8086,27a2) VGA device PCI IDs


<source lang = bash>
That's it, exit configuration, and run make to get your VGA enabled coreboot image.
device pci 9.0 on  # PCI
        chip drivers/pci/onboard
                device pci 9.0 on end
                register "rom_address" = "0xfff80000" #512k image
                #register "rom_address" = "0xfff00000" #1M image
        end
end
</source>


Replace the 9.0 with the dev.fn of your vga device.  You can find this number by doing a 'lspci' from the board booted under linux.
== How to retrieve a good video bios ==
Please make sure the device number is correct. Otherwise the config code can not compute the proper ROM address.


There are various ways to get hold of the video bios blob and not all work equally good for all boards (rather the opposite).


==== How to compute the "rom_address" value ====
The best way is to extract it from the vendor firmware.
ROM (called 'flash' a lot) chips are located directly below 4Gbyte  (0xffffffff) boundary.
In the case of a traditional x86 BIOS this is rather easy and very reliable.
On UEFI systems there does not seem to be a unified way of success but sometimes the steps below work.


So you need to calculate the address by subtracting the
Another category is downloading the blobs directly.
flash chip size (and adding the offset within the image)
Some vendors offer them in graphics driver packages etc. and you might even find them on enthusiasts website dedicated to firmware modding etc.


In coreboot the offset within the image is 0, because its the first
The most delicate ways are by dumping the blob from a running system.
thing in the coreboot image.
This might sound like the most reasonable way but the image present after boot might not be the same as it is (to be) stored in flash (e.g. if it is self modifying).
However, in some cases this is the only way and then it is quite comfortable.


So you need to compute the address in the systems memory space where the start of the video bios will show up.
=== RECOMMENDED: Extracting from your vendor bios image ===


To do this you take the 4Gb of address and subtract the size of your coreboot image.
The recommended method is to take your mainboard vendor's BIOS image (if there is one) and extract the VGA BIOS using a tool called [[bios_extract]].
0x100000000 - (ROM size in Kb * 1024)


You can do this in bash by:
$ git clone http://review.coreboot.org/p/bios_extract.git


biossize=256
This is the most reliable way:
printf "0x%x\n" $(( 0x100000000 - ($biossize*1024) ))
* You are guaranteed to get an image that fits to your onboard VGA
* Even if your VGA BIOS uses self-modifying code you get a correct image


Addresses for popular chip sizes:
Decompress your rom image with:
  256K  0xfffc0000
  $ ./bios_extract hdmag217.rom
512k  0xfff80000
1024k 0xfff00000


If bios_decode fails with a message like
Using file "hdmag217.rom" (513kB)
Found Phoenix BIOS "Phoenix ServerBIOS 3 Release 6.0    "
Version "DEVEL4E0", created on 03/20/06 at 14:37:39.
Error: Invalid module signature at 0x80581


=== Target Configuration ===
then you have to cut the flash chip description off the image. In this case the BIOS image is 512KB, so you do
$ dd if=hdmag217.rom of=hdma.rom bs=512k count=1
1+0 records in
1+0 records out
524288 bytes transferred in 0.000883 secs (593688784 bytes/sec)


2. You still need to modify your target 'Config.lb' to reserve space for the additional video bios.  Reduce the size of your coreboot image by the size of the video bios. You will prepend the video bios to the coreboot image in step 3.


in the normal section
You will get an output similar to this:


<source lang="bash">
Using file "hdma.rom" (512kB)
romimage "normal"
Found Phoenix BIOS "Phoenix ServerBIOS 3 Release 6.0    "
#      48K for SCSI FW or ATI ROM
Version "DEVEL4E0", created on 03/20/06 at 14:37:39.
option ROM_SIZE = 475136
0x715FC ( 27134 bytes)  ->  romexec_0.rom
</source>
0x6E1CB ( 13338 bytes)  ->  strings_0.rom (29401 bytes)
0x6D65D (  2899 bytes)  ->  display_0.rom (4128 bytes)
0x6B62E (  8208 bytes)  ->  update_0.rom
0x6B1E3 (  1072 bytes)  ->  decompcode_0.rom [0x5000:0xB6D0]
0x6564F ( 23421 bytes)  ->  oprom_0.rom (36864 bytes)
0x65608 (    44 bytes)  ->  tcpa_H_0.rom (32 bytes)
0x65592 (    91 bytes)  ->  acpi_1.rom (116 bytes)
0x65519 (    94 bytes)  ->  acpi_2.rom (244 bytes)
0x654ED (    13 bytes)  ->  tcpa_*_0.rom
0x64D4F (  1927 bytes)  ->  bioscode_0.rom (31382 bytes) [0xF000:0x856A]
0x60020 ( 19728 bytes)  ->  romexec_1.rom
0x570D9 ( 36656 bytes)  ->  oprom_1.rom (61440 bytes)
0x4DB9D ( 38177 bytes)  ->  oprom_2.rom (63488 bytes)
0x46493 ( 30447 bytes)  ->  oprom_3.rom (65536 bytes)
0x41DAB ( 18125 bytes)  ->  logo_0.rom (310162 bytes)
0x39CA5 ( 25439 bytes)  ->  oprom_4.rom (51200 bytes)
0x36005 ( 15493 bytes)  ->  setup_0.rom (37682 bytes)
0x325D7 ( 14867 bytes)  ->  template_0.rom (37728 bytes)
0x2FA36 ( 11142 bytes)  ->  miser_0.rom (16208 bytes)
0x2E63C (  5087 bytes)  ->  tcpa_Q_0.rom (16096 bytes)
0x2D7C3 (  3678 bytes)  ->  acpi_0.rom (10464 bytes)
0x1FA2A ( 41023 bytes)  ->  bioscode_1.rom (56080 bytes) [0xE000:0x40F0]
0x14FE0 ( 43567 bytes)  ->  bioscode_2.rom (62416 bytes) [0x6000:0xCC30]
0x0EB4C ( 25721 bytes)  ->  bioscode_3.rom (36976 bytes) [0x6000:0x3BC0]
0x0D0A0 (  6801 bytes)  ->   bioscode_4.rom (31856 bytes) [0x5000:0xBF50]


or if you only have a "fallback" boot then use the "fallback" section instead.
Now you can check the option roms (oprom_?.rom) with the tool romheaders which is part of the [http://www.openfirmware.info/FCODE_suite FCode Suite] (in debian-based distros, you can get it by installing the '''fcode-utils''' package):


In the above example the bios chip is 512Kb part.  The video bios is 48Kb. So (512*1024)-(48*1024) = 475136.
$ romheaders oprom_0.rom
Image 1:
PCI Expansion ROM Header:
  Signature: 0x55aa (Ok)
  CPU unique data: 0x48 0xeb 0x7b 0x01 0x76 0x00 0x00 0x00
                    0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
  Pointer to PCI Data Structure: 0x017c
   
  PCI Data Structure:
  Signature: 0x50434952 'PCIR' (Ok)
  Vendor ID: 0x1002
  Device ID: 0x4752
  Vital Product Data: 0x0000
  PCI Data Structure Length: 0x0018 (24 bytes)
  PCI Data Structure Revision: 0x00
  Class Code: 0x030000 (VGA Display controller)
  Image Length: 0x0048 blocks (36864 bytes)
  Revision Level of Code/Data: 0x0421
  Code Type: 0x00 (Intel x86)
  Last-Image Flag: 0x80 (last image in rom)
  Reserved: 0x0000
Platform specific data for x86 compliant option rom:
  Initialization Size: 0x48 (36864 bytes)
  Entry point for INIT function: 0x80


=== Creating an Image ===
Congratulations, that's your option rom (compare PCI IDs and Class Code to find it among the option roms).


3. Finally, prepend your video bios to the coreboot.rom
=== UEFI Method ===


<source lang="bash">
UEFI's format is more structured than that of a traditional flat binary BIOS. In order to extract the VBIOS Option ROM you will need
cat <videobios.bin> coreboot.rom > final_coreboot.rom
to parse out the UEFI Volumes and sub-Volumes out the UEFI filesystem using the [https://github.com/LongSoft/UEFITool UEFITool].
</source>


where <videobios.bin> is the name of your video bios image.
* Look for the " CSMCORE " DXE Driver ? usually having the hash 'a062cf1f-8473-4aa3-8793-600bc4ffe9a8'?
You need to make sure the final_coreboot.rom size is the size of your ROM chip.  Normally 256kb, 512kb, or 1024Kb.
* Search for text "VGA Compatible BIOS" ('''uncheck unicode''')
* Search for text "PCIR" ('''uncheck unicode''')


dd is helpfull to get your <videobios.bin> when booted under the  factory BIOS.
Double clicking the matching line in the "Messages" section should select the appropriate RAW section. From the menu select "Action -> Section -> Extract Body...".


=== Downloading ===


== How to retrieve a good video bios ==
There are sites that have video BIOS ROMs on their website (with all implications of retrieving a binary from an unknown source and executing it...).


=== Extracting from your vendor bios image ===
For Intel onboard graphics you can download the vbios (vga bios) from Intel's download section. The vbios is included with some versions of the graphics driver. The summary will say something like "NOTE:These materials are intended for use by developers.Includes VBIOS". The actual vbios file is the *.dat file included with the graphics driver.


The recommended method is to take your mainboard vendor's BIOS image and extract the VGA BIOS using a tool called awardeco/amideco/phnxdeco. This is the most reliable way:
=== Retrieval via Linux kernel ===
* You are guaranteed to get an image that fits to your onboard VGA
Some Linux drivers (e.g. <tt>radeon</tt> for AMD) make option ROMs like the video blob available to user space via sysfs.
* Even if your VGA BIOS uses self-modifying code you get a correct image
To use that to get the blob you need to enable it first.
To that end you need to determine the path within <tt>/sys</tt> corresponding to your graphics chip.
It looks like this: <tt>/sys/devices/pci<domain>:<bus>/<domain>:<bus>:<slot>.<function>/rom</tt>.


=== Downloading ===
You can get the respective information with <tt>lspci</tt>, for example:
# lspci -tv
-[0000:00]-+-00.0  Advanced Micro Devices, Inc. [AMD] Family 16h Processor Root Complex
            +-01.0  Advanced Micro Devices, Inc. [AMD/ATI] Kabini [Radeon HD 8210]
...


There are sites that have video bios roms on their website. (I know of this one for nvidia cards: [http://whitebunny.demon.nl/hardware/chipset_nvidia.html])
Here the the needed bits (for the ROM of the Kabini device) are:
* PCI domain: (almost always) 0000
* PCI bus: (also very commonly) 00
* PCI slot: 01 (logical slot; different from any physical slots)
* PCI function: 0 (a PCI device might have multiple functions... shouldn't matter here)


=== Extracting from the system ===
To enable reading of the ROM you need to write 1 to the respective file, e.g.:


However you should be able to retrieve your own video bios as well with linux.
echo 1 > /sys/devices/pci0000:00/0000:00:01.0/rom
* Boot up a machine with a commercial bios (not coreboot) with the video card you wish to work under coreboot.
* From the command line enter:<br /><code>dd if=/dev/mem of=vgabios.bin skip=1536 count=128 or <br />dd if=/dev/mem of=vgabios.bin bs=1k count=64 skip=768<br />This assumes you card's bios is cached at 0xc0000, and is 64K long. You<br />can see where and how much your card's bios is using by<br />doing a cat iomem | grep "Video ROM"<br /></code>
** dd Explained (man dd to learn more):
***  if is the location to retrieve from.
***  of is the output file (your rom image)
***  skip jumps n blocks where the default n is 512 bytes
***  count is how many blocks you wish to read
***  bs is the block size
* You now have a video bios image


==== Perl script to dump out your video bios ====
The same file should then contain the video blob and it should be possible to simply copy it, e.g.:


This is a simple script that computes the size and offset then uses
cp /sys/devices/pci0000:00/0000:00:01.0/rom vgabios.bin
the command dd to dump your video bios to a file.


<source lang="perl">
<tt>romheaders</tt> should print reasonable output for this file.
#!/usr/bin/perl
($range, $info) = split /:/, `grep "Video ROM" /proc/iomem`;
($start, $end) = split /-/, $range;
if( $start eq "" ) {
        print "Couldn't find Video ROM in /proc/iomem\n";
        exit;
}
$offset = hex "0x$start";
$tmp = hex "0x$end";
$size = 1 + $tmp - $offset;
$command = "dd if=/dev/mem of=saved_vgabios.bin bs=1c count=$size skip=$offset";
print "range = $range, start = $start, size = $size\n";
print "$command\n";
system $command;
</source>


= VGA initialization in coreboot v3 =
Intel Graphics supports this method. See [https://01.org/linuxgraphics/documentation/development/how-dump-video-bios How to dump Video BIOS].


In coreboot v3 you have to set your PCI option ROM execution method under the '''Device''' menu. The default is x86emu. To get a smaller (and slightly more insecure) version, you can switch to vm86. If you don't want option rom execution, set it to Disabled.
=== Extraction from mapped memory (if everything else fails) ===


== On-board devices ==
However you might be able to retrieve your on-board video BIOS with Linux as well.
 
To add option roms for on-board video cards to your coreboot image, you can just add the image using lar:


* Boot up a machine with a commercial BIOS (not coreboot) with the video card you wish to work under coreboot.
* You can see where and how much your card's bios is using by doing a
<source lang="bash">grep 'Video ROM' /proc/iomem</source>
* From the command line enter:<br /><source lang="bash">dd if=/dev/mem of=vgabios.bin bs=1k count=64 skip=768</source> This assumes you card's BIOS is cached at 0xc0000, and is 64K long.
<br /><source lang="bash">dd if=/dev/mem of=video.bios.bin.4 bs=65536 count=1 skip=12</source>
This works for many of the VIA Epia boards.<br>
Alternatively you can automatically generate it using this nice script from Peter Stuge:<br />
<source lang="bash">
<source lang="bash">
lar -C lzma -a coreboot.rom vgabios.rom:pciXXXX,YYYY.rom
cat /proc/iomem | grep 'Video ROM' | (read m; m=${m/ :*}; s=${m/-*}; e=${m/*-}; \
dd if=/dev/mem of=vgabios.bin bs=1c skip=$[0x$s] count=$[$[0x$e]-$[0x$s]+1])
</source>
</source>
* You (might) have a video BIOS image now. Check it at least with romheaders (as described above).
== YABEL ==
* Yabel can be used to trace the VGA option rom.
* However its ability to prevent the option rom to do nasty things is limited: Often the GPU offers a way (e.g. trough an IO BAR) to access arbitrary locations in RAM, so limiting access of the GPU's PCI device to the option rom wouldn't contain it completely.
See [[Coreboot Options]] for more information about the option.


In the above example, vgabios.rom is the name of your option rom on disk. XXXX is the PCI vendor ID of your on-board video adapter and YYYY is its PCI device ID.
[[Category:Blobs]]

Latest revision as of 14:47, 12 April 2016

VGA initialization in coreboot

Since coreboot v4 you can configure VGA initialization in Kconfig. For older versions of coreboot check the history of this page.

First do:

<source lang="bash"> 

$ make menuconfig

</source>

Then go 

    Chipset  --->
     [*] Setup bridges on path to VGA adapter 
     [*] Run VGA option ROMs
     Option ROM execution type (Native mode)  --->

Alternatively you can choose the "Secure mode" to run the VGA option rom in a contained environment.

If you have no on-board graphics, you are done configuring coreboot at this point. You may exit configuration, and run make to get your VGA enabled coreboot image.

On-board Video Devices

If you run coreboot on a system with on-board graphics, you have to embed a VGA on the top level, enter the file name of your option rom and the PCI ID of the associated graphics device in the form <vendor_id>,<device_id>: 

   VGA BIOS  --->
    [*] Add a VGA BIOS image
    (oprom-0.rom) VGA BIOS path and filename
    (8086,27a2) VGA device PCI IDs

That's it, exit configuration, and run make to get your VGA enabled coreboot image.

How to retrieve a good video bios

There are various ways to get hold of the video bios blob and not all work equally good for all boards (rather the opposite).

The best way is to extract it from the vendor firmware. In the case of a traditional x86 BIOS this is rather easy and very reliable. On UEFI systems there does not seem to be a unified way of success but sometimes the steps below work.

Another category is downloading the blobs directly. Some vendors offer them in graphics driver packages etc. and you might even find them on enthusiasts website dedicated to firmware modding etc.

The most delicate ways are by dumping the blob from a running system. This might sound like the most reasonable way but the image present after boot might not be the same as it is (to be) stored in flash (e.g. if it is self modifying). However, in some cases this is the only way and then it is quite comfortable.

RECOMMENDED: Extracting from your vendor bios image

The recommended method is to take your mainboard vendor's BIOS image (if there is one) and extract the VGA BIOS using a tool called bios_extract. 

$ git clone http://review.coreboot.org/p/bios_extract.git

This is the most reliable way:

  • You are guaranteed to get an image that fits to your onboard VGA
  • Even if your VGA BIOS uses self-modifying code you get a correct image

Decompress your rom image with: 

$ ./bios_extract hdmag217.rom

If bios_decode fails with a message like 

Using file "hdmag217.rom" (513kB)
Found Phoenix BIOS "Phoenix ServerBIOS 3 Release 6.0     "
Version "DEVEL4E0", created on 03/20/06 at 14:37:39.
Error: Invalid module signature at 0x80581

then you have to cut the flash chip description off the image. In this case the BIOS image is 512KB, so you do 

$ dd if=hdmag217.rom of=hdma.rom bs=512k count=1
1+0 records in
1+0 records out
524288 bytes transferred in 0.000883 secs (593688784 bytes/sec)


You will get an output similar to this: 

Using file "hdma.rom" (512kB)
Found Phoenix BIOS "Phoenix ServerBIOS 3 Release 6.0     "
Version "DEVEL4E0", created on 03/20/06 at 14:37:39.
0x715FC ( 27134 bytes)   ->   romexec_0.rom
0x6E1CB ( 13338 bytes)   ->   strings_0.rom	(29401 bytes)
0x6D65D (  2899 bytes)   ->   display_0.rom	(4128 bytes)
0x6B62E (  8208 bytes)   ->   update_0.rom
0x6B1E3 (  1072 bytes)   ->   decompcode_0.rom			 [0x5000:0xB6D0]
0x6564F ( 23421 bytes)   ->   oprom_0.rom	(36864 bytes)
0x65608 (    44 bytes)   ->   tcpa_H_0.rom	(32 bytes)
0x65592 (    91 bytes)   ->   acpi_1.rom	(116 bytes)
0x65519 (    94 bytes)   ->   acpi_2.rom	(244 bytes)
0x654ED (    13 bytes)   ->   tcpa_*_0.rom
0x64D4F (  1927 bytes)   ->   bioscode_0.rom	(31382 bytes)	 [0xF000:0x856A]
0x60020 ( 19728 bytes)   ->   romexec_1.rom
0x570D9 ( 36656 bytes)   ->   oprom_1.rom	(61440 bytes)
0x4DB9D ( 38177 bytes)   ->   oprom_2.rom	(63488 bytes)
0x46493 ( 30447 bytes)   ->   oprom_3.rom	(65536 bytes)
0x41DAB ( 18125 bytes)   ->   logo_0.rom	(310162 bytes)
0x39CA5 ( 25439 bytes)   ->   oprom_4.rom	(51200 bytes)
0x36005 ( 15493 bytes)   ->   setup_0.rom	(37682 bytes)
0x325D7 ( 14867 bytes)   ->   template_0.rom	(37728 bytes)
0x2FA36 ( 11142 bytes)   ->   miser_0.rom	(16208 bytes)
0x2E63C (  5087 bytes)   ->   tcpa_Q_0.rom	(16096 bytes)
0x2D7C3 (  3678 bytes)   ->   acpi_0.rom	(10464 bytes)
0x1FA2A ( 41023 bytes)   ->   bioscode_1.rom	(56080 bytes)	 [0xE000:0x40F0]
0x14FE0 ( 43567 bytes)   ->   bioscode_2.rom	(62416 bytes)	 [0x6000:0xCC30]
0x0EB4C ( 25721 bytes)   ->   bioscode_3.rom	(36976 bytes)	 [0x6000:0x3BC0]
0x0D0A0 (  6801 bytes)   ->   bioscode_4.rom	(31856 bytes)	 [0x5000:0xBF50]

Now you can check the option roms (oprom_?.rom) with the tool romheaders which is part of the FCode Suite (in debian-based distros, you can get it by installing the fcode-utils package): 

$ romheaders oprom_0.rom 

Image 1:
PCI Expansion ROM Header:
  Signature: 0x55aa (Ok)
  CPU unique data: 0x48 0xeb 0x7b 0x01 0x76 0x00 0x00 0x00
                   0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
  Pointer to PCI Data Structure: 0x017c

PCI Data Structure:
  Signature: 0x50434952 'PCIR' (Ok)
  Vendor ID: 0x1002
  Device ID: 0x4752
  Vital Product Data:  0x0000
  PCI Data Structure Length: 0x0018 (24 bytes)
  PCI Data Structure Revision: 0x00
  Class Code: 0x030000 (VGA Display controller)
  Image Length: 0x0048 blocks (36864 bytes)
  Revision Level of Code/Data: 0x0421
  Code Type: 0x00 (Intel x86)
  Last-Image Flag: 0x80 (last image in rom)
  Reserved: 0x0000

Platform specific data for x86 compliant option rom:
  Initialization Size: 0x48 (36864 bytes)
  Entry point for INIT function: 0x80

Congratulations, that's your option rom (compare PCI IDs and Class Code to find it among the option roms).

UEFI Method

UEFI's format is more structured than that of a traditional flat binary BIOS. In order to extract the VBIOS Option ROM you will need to parse out the UEFI Volumes and sub-Volumes out the UEFI filesystem using the UEFITool.

  • Look for the " CSMCORE " DXE Driver ? usually having the hash 'a062cf1f-8473-4aa3-8793-600bc4ffe9a8'?
  • Search for text "VGA Compatible BIOS" (uncheck unicode)
  • Search for text "PCIR" (uncheck unicode)

Double clicking the matching line in the "Messages" section should select the appropriate RAW section. From the menu select "Action -> Section -> Extract Body...".

Downloading

There are sites that have video BIOS ROMs on their website (with all implications of retrieving a binary from an unknown source and executing it...).

For Intel onboard graphics you can download the vbios (vga bios) from Intel's download section. The vbios is included with some versions of the graphics driver. The summary will say something like "NOTE:These materials are intended for use by developers.Includes VBIOS". The actual vbios file is the *.dat file included with the graphics driver.

Retrieval via Linux kernel

Some Linux drivers (e.g. radeon for AMD) make option ROMs like the video blob available to user space via sysfs. To use that to get the blob you need to enable it first. To that end you need to determine the path within /sys corresponding to your graphics chip. It looks like this: /sys/devices/pci<domain>:<bus>/<domain>:<bus>:<slot>.<function>/rom.

You can get the respective information with lspci, for example: 

# lspci -tv
-[0000:00]-+-00.0  Advanced Micro Devices, Inc. [AMD] Family 16h Processor Root Complex
           +-01.0  Advanced Micro Devices, Inc. [AMD/ATI] Kabini [Radeon HD 8210]
...

Here the the needed bits (for the ROM of the Kabini device) are:

  • PCI domain: (almost always) 0000
  • PCI bus: (also very commonly) 00
  • PCI slot: 01 (logical slot; different from any physical slots)
  • PCI function: 0 (a PCI device might have multiple functions... shouldn't matter here)

To enable reading of the ROM you need to write 1 to the respective file, e.g.: 

echo 1 > /sys/devices/pci0000:00/0000:00:01.0/rom

The same file should then contain the video blob and it should be possible to simply copy it, e.g.: 

cp /sys/devices/pci0000:00/0000:00:01.0/rom vgabios.bin

romheaders should print reasonable output for this file.

Intel Graphics supports this method. See How to dump Video BIOS.

Extraction from mapped memory (if everything else fails)

However you might be able to retrieve your on-board video BIOS with Linux as well.

  • Boot up a machine with a commercial BIOS (not coreboot) with the video card you wish to work under coreboot.
  • You can see where and how much your card's bios is using by doing a

<source lang="bash">grep 'Video ROM' /proc/iomem</source>

  • From the command line enter:
    <source lang="bash">dd if=/dev/mem of=vgabios.bin bs=1k count=64 skip=768</source> This assumes you card's BIOS is cached at 0xc0000, and is 64K long.


<source lang="bash">dd if=/dev/mem of=video.bios.bin.4 bs=65536 count=1 skip=12</source> This works for many of the VIA Epia boards.
Alternatively you can automatically generate it using this nice script from Peter Stuge:
<source lang="bash"> cat /proc/iomem | grep 'Video ROM' | (read m; m=${m/ :*}; s=${m/-*}; e=${m/*-}; \ dd if=/dev/mem of=vgabios.bin bs=1c skip=$[0x$s] count=$[$[0x$e]-$[0x$s]+1]) </source>

  • You (might) have a video BIOS image now. Check it at least with romheaders (as described above).

YABEL

  • Yabel can be used to trace the VGA option rom.
  • However its ability to prevent the option rom to do nasty things is limited: Often the GPU offers a way (e.g. trough an IO BAR) to access arbitrary locations in RAM, so limiting access of the GPU's PCI device to the option rom wouldn't contain it completely.

See Coreboot Options for more information about the option.

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