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

[Chris Wilson]

On Wed, Feb 22, 2017 at 10:15:12AM +0200, Jani Nikula wrote:
> 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. ;)

No worries, all I wanted was a very short step-by-step guide as to how
one would experiment with, use, or test this feature.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre