[Bug 71701] [ivb dp aux dp-to-vga dongle regression] i915 DisplayPort link training via DP-to-VGA dongle, blank screen

[bugzilla-daemon at bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=71701

--- Comment #36 from Kris Karas <bugs-a13 at moonlit-rail.com> ---
The patch suggest by Jani in Comment #35 is getting close.

Here's a status of what works and what doesn't by kernel version:
    Linux <= 3.13.5
        Bug-free, no warnings.
    Linux >= 3.13.6 < 3.17.x
        Better initialization on boot most of the time.
    Linux >= 3.18.x
        Initialized correctly on boot all of the time.
        Fails to re-initialize after VESA power-off about 50% of the time.
        Switching from X-server to console and back to X (c-a-F1 + c-a-F7)
        will correctly re-initialize all the time.
    Linux 3.18.7 with patch from Comment #35
        No visual bugs, display (re)initializes 100% of the time.
        About 75% of the time, re-initializing after VESA power-off shows:
        "[drm:intel_dp_start_link_train] *ERROR* failed to enable link
training"
        in the kernel log, although the screen/dongle appears to work properly.

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