Troubleshooting LVDS on GM45 (kernel 4.5.0)

[Ville Syrjälä]

On Mon, Apr 04, 2016 at 11:14:45AM +0800, Rob Kramer wrote:
> I've tried again without video parameter -- same outcome. I've also 
> applied Ville's patch "drm/i915: Read timings from the correct 
> transcoder in intel_crtc_mode_get()" (with teeny backport fix). It seems 
> this code is never called in my case though, since intel_lvds_init() 
> chooses to use the VBT mode instead. Log is uploaded here: 
> http://pastebin.com/bGa2UvLu

That's a bit odd. The 3.14 kernel definitely chose to use the current
pipe timings instead of the VBT mode:
[    5.504033] [drm:intel_lvds_init], using current (BIOS) mode:
[    5.504037] [drm:drm_mode_debug_printmodeline], Modeline 0:"640x480" 0 148571 640 656 752 800 480 490 492 525 0x0 0x0

Although it looks like it did find a mode in the VBT as well:
[    5.502056] [drm:parse_lfp_panel_data], Found panel mode in BIOS VBT tables:
[    5.502060] [drm:drm_mode_debug_printmodeline], Modeline 0:"1024x768" 0 65000 1024 1048 1184 1344 768 771 777 806 0x8 0xa
so now I'm rather confused as to how it managed to not use it.

> 
> 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.

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.

> 
> Cheers!
> 
>        Rob
> 
> 
> On 04/01/2016 07:11 PM, Jani Nikula wrote:
> >
> > Apr  1 11:32:21 vides user.err kernel: [    4.896341] [drm:i9xx_crtc_compute_clock [i915]] *ERROR* Couldn't find PLL settings for mode!
> >
> > Please try without the kernel command line mode.
> >
> > BR,
> > Jani.
> >

-- 
Ville Syrjälä
Intel OTC