Re: [coreboot] VGA and Graphics

[Patrick Rudolph]

VBT is documented by intel-gpu-tools. There's intel_vbt_decode (former intel_bios_decode) available https://cgit.freedesktop.org/xorg/app/intel-gpu-tools/tree/tools/intel_vbt_d... that will print all tables in human readable form.
Regards Patrick

Am 4. April 2017 20:45:15 MESZ schrieb Nico Huber :
> Hi Ron,
>
> On 04.04.2017 19:46, ron minnich wrote:
> > Igor, if you are going to say things like "AFAIK there is no public
> > description of these tables' layout and contents, only Intel knows
>
> how to
> > build and parse them.", it's really a good idea to back it up with a
> > primary source, especially since you also use phrases like "I assume"
>
> and
> > "I guess". I am pretty sure you're wrong in this case. The V in VBT,
>
> as I
> > understand it, means VESA, and VESA has been a standard for about 30
>
> years.
> > Please, everyone, if you're going to move this conversation forward,
>
> you
> > need to cite primary sources at least, such as this one:
> > http://www.petesqbsite.com/sections/tutorials/tuts/vbe3.pdf.
>
> now you got confused too. I'll try to clarify.
>
> VBE means VESA (Video Electronics Standards Association) BIOS
> Extension.
> It's a Video BIOS interface extension (i.e. specifying additional BIOS
> calls). Don't know if it was public from the beginning (you often have
> to be a VESA member to get access to their "standards"), but the inter-
> face is used by many open source programs. It's vendor independent.
> Also
> it's off-topic, nobody was discussing it here.
>
> As Igor noted, VBE has absolutely nothing to do with VBT.
>
> VBT means Video BIOS Table. It's a 100% Intel specific table of confi-
> guration options for Intel's Video BIOS and Intel's graphics drivers.
> There is no public documentation, but as it's used by the Linux driver,
> at least the structure and some of the values are publicly "documented"
> [1]. Developers of the i915 Linux driver stated that they are not wil-
> ling to support systems without a VBT. Most features of the i915 driver
> work without a VBT by chance. But anything board specific, like inte-
> grated panels in laptops, will likely _not_ work. I'd also expect that
> they won't count it as a regression if something breaks but would still
> work with a VBT. (Windows won't even try to get things running without
> VBT, AFAIK.)
>
> An OEM should have access to Intel's binary configuration tool and the
> specification file for the VBT of his processor's generation. It comes
> along with the VBIOS, I suppose.
>
> Nico
>
> PS. Igor, Zoran please write text-only emails or at least make sure the
>    text version is readable and quotes are visible as quotes.
>
> [1]
> https://www.kernel.org/doc/html/latest/gpu/i915.html#video-bios-table-vbt

VGA and Graphics

[Igor Skochinsky]

Hello Patrick,

Tuesday, April 4, 2017, 8:54:09 PM, you wrote:

PR> VBT is documented by intel-gpu-tools. There's intel_vbt_decode
PR> (former intel_bios_decode) available
PR> https://cgit.freedesktop.org/xorg/app/intel-gpu-tools/tree/tools/intel_vbt_d...
PR> that will print all tables in human readable form.

Nice find! I did not realize this tool supports that many structures;
for some reason I thought it just prints some general info without details.

So now that we have a dumper the following should be possible:
1) make a "decompiler" that would convert VBT from the option ROM into a human/machine
readable text format
2) make a "compiler" that would take that text format and create a
binary VBT from it
3) put the binary VBT into the ACPI IGD OpRegion table ([1], [2]), or
wherever the graphics driver can find it.

So, basically, an approach similar to ich9gen for the flash
descriptor/gbe.

This should allow getting rid of the option ROM if real mode support is
not required.

[1] https://01.org/sites/default/files/documentation/acpi_igd_opregion_spec_0.pd...
[2] https://lwn.net/Articles/429319/

PR> Am 4. April 2017 20:45:15 MESZ schrieb Nico Huber :
PR> Hi Ron,

PR> On 04.04.2017 19:46, ron minnich wrote:
PR>  Igor, if you are going to say things like "AFAIK there is no public
PR>  description of these tables' layout and contents, only Intel knows how to
PR>  build and parse them.", it's really a good idea to back it up with a
PR>  primary source, especially since you also use phrases like "I assume" and
PR>  "I guess". I am pretty sure you're wrong in this case. The V in VBT, as I
PR>  understand it, means VESA, and VESA has been a standard for about 30 years.
PR>  
PR>  Please, everyone, if you're going to move this conversation forward, you
PR>  need to cite primary sources at least, such as this one:
PR>  http://www.petesqbsite.com/sections/tutorials/tuts/vbe3.pdf.

PR> now you got confused too. I'll try to clarify.

PR> VBE means VESA (Video Electronics Standards Association) BIOS Extension.
PR> It's a Video BIOS interface extension (i.e. specifying additional BIOS
PR> calls). Don't know if it was public from the beginning (you often have
PR> to be a VESA member to get access to their "standards"), but the inter-
PR> face is used by many open source programs. It's vendor independent. Also
PR> it's off-topic, nobody was discussing it here.

PR> As Igor noted, VBE has absolutely nothing to do with VBT.

PR> VBT means Video BIOS Table. It's a 100% Intel specific table of confi-
PR> guration options for Intel's Video BIOS and Intel's graphics drivers.
PR> There is no public documentation, but as it's used by the Linux driver,
PR> at least the structure and some of the values are publicly "documented"
PR> [1]. Developers of the i915 Linux driver stated that they are not wil-
PR> ling to support systems without a VBT. Most features of the i915 driver
PR> work without a VBT by chance. But anything board specific, like inte-
PR> grated panels in laptops, will likely _not_ work. I'd also expect that
PR> they won't count it as a regression if something breaks but would still
PR> work with a VBT. (Windows won't even try to get things running without
PR> VBT, AFAIK.)

PR> An OEM should have access to Intel's binary configuration tool and the
PR> specification file for the VBT of his processor's generation. It comes
PR> along with the VBIOS, I suppose.

PR> Nico

PR> PS. Igor, Zoran please write text-only emails or at least make sure the
PR>     text version is readable and quotes are visible as quotes.

PR> [1]
PR> https://www.kernel.org/doc/html/latest/gpu/i915.html#video-bios-table-vbt

VGA and Graphics

[Arthur Heymans]

Igor Skochinsky via coreboot  writes:
> Hello Patrick,
>
> Tuesday, April 4, 2017, 8:54:09 PM, you wrote:
>
> PR> VBT is documented by intel-gpu-tools. There's intel_vbt_decode
> PR> (former intel_bios_decode) available
> PR> https://cgit.freedesktop.org/xorg/app/intel-gpu-tools/tree/tools/intel_vbt_d...
> PR> that will print all tables in human readable form.
>
> Nice find! I did not realize this tool supports that many structures;
> for some reason I thought it just prints some general info without details.
>
> So now that we have a dumper the following should be possible:
> make a "decompiler" that would convert VBT from the option ROM into a human/machine
>
> readable text format
> 2) make a "compiler" that would take that text format and create a
> binary VBT from it
> 3) put the binary VBT into the ACPI IGD OpRegion table ([1], [2]), or
> wherever the graphics driver can find it.

I think blobtool would fit that purpose quite nicely on the assumption
VBT is already extracted and that VBT has fixed locations for its
entries.  If one writes a blobtool spec file (which describes the
bitfields) it can serve both as a "decompiler" and as a "compiler".
> So, basically, an approach similar to ich9gen for the flash
> descriptor/gbe.

Blobtool handles ICH9 IFD and GBE compilation and decompilation too. ;)
> This should allow getting rid of the option ROM if real mode support is
> not required.

Would great to have indeed, who knows if other OS drivers will mandate
VBT one day.

Kind regards.