Troubleshooting LVDS on GM45 (kernel 4.5.0)

[Rob Kramer]

On 04/04/2016 10:58 PM, Ville Syrjälä wrote:
>
>> Since this VBT mode is probably junk anyway, I commented out the
>> if-statement that selects it (in intel_lvds.c), so that the code will
>> pick the mode as set by BIOS. The result is much better, I actually get
>> proper looking output! X also runs well on top of that.
>>
>> There are still several errors in the log file though (probably caused
>> by my little hack), see here: http://pastebin.com/UbCjizSV.
>>
>> Is using the mode as set up by BIOS the way to go for LVDS? If so, is
>> there a module parameter that can force this, or force the bogus VBT to
>> be disregarded?
> Can you provide a dump of /sys/kernel/debug/dri/0/i915_opregion ?
>
> Maybe file a bug in bugs.freedesktop.org and attach it (and the dmesg
> logs you already have) there so we don't lose these.

Sure! I added the opregion blob to the newly opened bug here: 
https://bugs.freedesktop.org/show_bug.cgi?id=94825

> You also said you can choose the panel type in the BIOS? Does it have
> some predefined set of panels or something? I would have assumed
> changing that might patch the VBT to point at the correct timings.
Yes, there's a list of modes, and the correct one is selected. I've 
added an image to the bug entry. I don't know if the 1024x768 mode 
mentioned in the boot log is the same as the 1024x768 mode in that bios 
list, or why only that mode is found..

I assume that the 1920x1080 at 148.5M mode was added by the vendor of the 
display set to match the panel that they use.

Cheers,

      Rob