Bug 97310

Summary: i915 Kernel Null pointer dereference - skylake
Product: DRI Reporter: gene <gjunk>
Component: DRM/IntelAssignee: Intel GFX Bugs mailing list <intel-gfx-bugs>
Status: CLOSED FIXED QA Contact: Intel GFX Bugs mailing list <intel-gfx-bugs>
Severity: normal    
Priority: medium CC: intel-gfx-bugs
Version: unspecified   
Hardware: x86-64 (AMD64)   
OS: Linux (All)   
Whiteboard:
i915 platform: SKL i915 features: display/Other
Attachments:
Description Flags
kernel log none

Description gene 2016-08-11 22:52:06 UTC
Created attachment 125722 [details]
kernel log

kernel:
   Happens with kernel 4.8-rc1 
   No issues with 4.7 kernel.

Hardware: intel NUC6i5SY

Once this bug is hit graphics there is no output on the display port at all. 

kernel log attached:
Comment 1 gene 2016-08-29 16:01:15 UTC
I tried with 4.8 rc4. While I still get no graphics output on the display port - switching to a virtual terminal works - the font is small (monitor is Dell 4K) but i get a prompt and can login fine.
Comment 2 gene 2016-09-26 15:18:55 UTC
Update - using 4.8.rc8 - same problem. 

I want to add however, that rebooting (hot or cold) repeatedly will eventually get graphics working - so it feels like a race of some kind. 

I do not see on this on any non skylake machines (tested 7 different machines).

g
Comment 3 gene 2016-10-09 16:13:07 UTC
Update: 
Multiple boots still needed using 4.8.1 kernel - to graphics output. Seems like a timing issue?  Enough cold reboots will eventually get graphics working and after that it seems totally fine. Its just getting it booted up with graphics.
Comment 4 Chris Wilson 2017-02-04 21:26:59 UTC
commit c45eb4fed12d278d3619f1904885bd0d7bcbf036 [4.8-rc2]
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date:   Wed Jul 13 18:34:45 2016 +0100

    drm/i915/fbdev: Check for the framebuffer before use

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