[Bug 96675] New: After commit f21a21983ef13a, the display is turned off

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=96675

            Bug ID: 96675
           Summary: After commit f21a21983ef13a, the display is turned off
           Product: DRI
           Version: unspecified
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: critical
          Priority: medium
         Component: DRM/Intel
          Assignee: intel-gfx-bugs at lists.freedesktop.org
          Reporter: larry.finger at lwfinger.net
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org

Created attachment 124717
  --> https://bugs.freedesktop.org/attachment.cgi?id=124717&action=edit
Output of dmesg with drm.debug=3 taken AFTER the faulty commit

As soon as kernel 4.7-rcX is started, the display is blanked, and it is never
turned on again. This problem was bisected to commit
f21a21983ef13a031250c4c3f6018e29a549d0f1
("drm/i915: Splitting intel_dp_detect"). The adapter in question is the
integrated graphics controller on a Toshiba Tecra A50 laptop. The output of
"lspci -nnv" for that controller is as follows: 

00:02.0 VGA compatible controller [0300]: Intel Corporation 4th Gen Core
Processor Integrated Graphics Controller [8086:0416] (rev 06) (prog-if 00 [VGA
controller])
        Subsystem: Toshiba America Info Systems Device [1179:0002]
        Flags: bus master, fast devsel, latency 0, IRQ 27
        Memory at e0000000 (64-bit, non-prefetchable) [size=4M]
        Memory at d0000000 (64-bit, prefetchable) [size=256M]
        I/O ports at 4000 [size=64]
        Expansion ROM at <unassigned> [disabled]
        Capabilities: [90] MSI: Enable+ Count=1/1 Maskable- 64bit-
        Capabilities: [d0] Power Management version 2
        Capabilities: [a4] PCI Advanced Features
        Kernel driver in use: i915
        Kernel modules: i915

Disabling i915 with a "nomodeset" on the kernel command line allows the system
to boot normally.

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