[Intel-gfx] [PATCH 5/5] drm/i915/opregion: let user specify override VBT via firmware load

[Jani Nikula]

On Tue, 21 Feb 2017, Chris Wilson <chris at chris-wilson.co.uk> wrote:
> On Tue, Feb 21, 2017 at 06:40:25PM +0200, Jani Nikula wrote:
>> Sometimes it would be most enlightening to debug systems by replacing
>> the VBT to be used. For example, in the referenced bug the BIOS provides
>> different VBT depending on the boot mode (UEFI vs. legacy). It would be
>> interesting to try the failing boot mode with the VBT from the working
>> boot, and see if that makes a difference.
>> 
>> Add a module parameter to load the VBT using the firmware loader, not
>> unlike the EDID firmware mechanism.
>
> What's the mechanism by which they would create a valid VBT file?
> Does
> 	cat /sys/kernel/debug/dri/0/i915_opregion > vbt.fw
> work and provide a starting point for corrections?
 
The debugfs file for just the VBT is i915_vbt.

For starters I only thought of using the VBT from the other boot mode,
and didn't really think of actually modifying the file, let alone making
it easy to modify the file using some tool for example.

There is a Windows-only BIOS Modification Program, or BMP, to modify the
VBT. It's referenced in a bunch of public documentation, but apparently
the tool itself is not publicly available. And even if it were, it's
neither free nor for Linux. I've never touched it myself.

Given the fact that we have tools/intel_vbt_decode in IGT, it should not
be hard to write such a tool. The information is all there for an
interested party. Just a SMOP. ;)

BR,
Jani.

-- 
Jani Nikula, Intel Open Source Technology Center