[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

Kris Karas <bugs-a13 at moonlit-rail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEEDINFO                    |VERIFIED
         Resolution|---                         |PATCH_ALREADY_AVAILABLE

--- Comment #39 from Kris Karas <bugs-a13 at moonlit-rail.com> ---
Kernel 4.1.0-rc8 shows the same behavior as kernels 3.19.x and above.
Screen (re)initializes visually, but kernel logs continue to be peppered with:
    [drm:intel_dp_start_link_train] *ERROR* failed to enable link training

Although there may be a forthcoming fix in the new codebase that will work for
kernel 4.1.x and above, this does not change the fact that this is a regression
introduced in kernel 3.13.6.  A patch to fix that regression has been available
for more than one year, and still remains unapplied!

Kernels 3.14 and 3.18 are both affected by this bug.  And they are in long-term
maintenance, requiring a patch.  Kernel 3.14's i915 code is sufficiently
different from 4.1 that a backport looks unlikely, necessitating a different
patch - which is, again, available and well-tested.

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