[Bug 104139] [CFL] Screen goes blank right after boot.

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=104139

--- Comment #8 from Kai-Heng Feng <kai.heng.feng at canonical.com> ---
(In reply to Rodrigo Vivi from comment #7)
> Sorry for not getting back sooner here...
> 
> So, VBT on this platform is bugged for sure. 6 is an invalid pin.
> 
> Anyways I double checked the code here and it is not possible if you have
> latest code there.
> 
> Since you are running with 
> 4.14.0-rc7+

The kernel I used is from
http://kernel.ubuntu.com/~kernel-ppa/mainline/drm-intel-nightly/.

Those kernels are built against intel-nightly tags. 
So the DRM and I915 are much newer than v4.14.0-rc7+.
I'll ask if put intel-nightly tags into version string is possible...

> 
> you probably have this patch applied:
> 75be7756bc21 ("drm/i915/cnl: Don't trust VBT's alternate pin for port D for
> now.")
> 
> but you are probably missing the proper fix:
> 9c3b2689d01f ("drm/i915/cnl: Map VBT DDC Pin to BSpec DDC Pin.")
> 
> Also probably a good idea to apply this one:
> c4fb60b9aba9 ("drm/i915/bios: add DP max link rate to VBT child device
> struct")
> 
> Could you please apply both patches and retest?

Sure. The new one is built against drm-intel-next-queued:
commit c4fb60b9aba9f939d3f8575df23fd8d5958ec6ed
(drm-intel/drm-intel-next-queued)
Author: Jani Nikula <jani.nikula at intel.com>
Date:   Thu Jan 18 17:33:10 2018 +0200

    drm/i915/bios: add DP max link rate to VBT child device struct

But the same code trace can be observed. Please see attached dmesg.

Also, this issue only happens when "Legacy ROM boot support" is enabled.

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