[Bug 94825] LVDS blank screen on GM45

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=94825

--- Comment #23 from Ville Syrjala <ville.syrjala at linux.intel.com> ---
(In reply to Rob Kramer from comment #22)
> (In reply to Ville Syrjala from comment #21)
> > I found something interesting in the opregion spec. Based on that I posted a
> > few patches that could help here:
> > https://lists.freedesktop.org/archives/intel-gfx/2016-April/091988.html
> > 
> > Please test and report back.
> 
> OK, reverted your previous _DDC patch, applied these three. The result is a
> blank screen. I added some debug statements in your opregion.c patch:
> 
> 	ret = swsci(dev, SWSCI_GBDA_PANEL_DETAILS, 0x0, &panel_details);
> 	if (ret)
> 	{
> 		DRM_DEBUG_KMS ("Rob: return %d\n", ret);
> 		return ret;
> 	}
> 
> 	DRM_DEBUG_KMS ("Rob: panel details 0x%x\n", panel_details);
> 
> And in the log:
> 
>   [drm:intel_opregion_get_panel_type] Rob: panel details 0x21000
> 
> Which would mean panel 0x10 according to the spec in your mail, which would
> be good if you'd started counting at 1 :)
> 
> Next, I tried setting the mode to 1366x768 at 73.8M in the bios, and the output
> changes to:
> 
>   [drm:intel_opregion_get_panel_type] Rob: panel details 0x20d00
> 
> That is off by one too, but is still good news since it follows the BIOS
> setting.. Trying the obvious fix works:
> 
>    return ((panel_details >> 8) & 0xff) - 1;
> 
> > "Bits [15:8] - Panel Type
> >  Bits contain the panel type user setting from CMOS
> >  00h = Not Valid, use default Panel Type & Timings from VBT
> >  01h - 0Fh = Panel Number"
> 
> That would mean only 15 possible valid modes, right? But my BIOS has 16 in
> its list already, and the correct mode happens to be the last one.
> 
> [No log attached, because nothing further of interest]

Thanks for testing. I found another version of the spec that says panel type 16
is still valid.

I posted new versions of patches 1 and 3. Please double check that they work
correctly.

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