[Bug 94825] LVDS blank screen on GM45

[bugzilla-daemon at freedesktop.org]

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

--- Comment #22 from Rob Kramer <rob at solution-space.com> ---
(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]

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