[Bug 90320] Lenovo ThinkPad E455 (Kaveri A10-7300): Blank built-in screen with radeon kms driver

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=90320

            Bug ID: 90320
           Summary: Lenovo ThinkPad E455 (Kaveri A10-7300): Blank built-in
                    screen with radeon kms driver
           Product: DRI
           Version: DRI git
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: blocker
          Priority: highest
         Component: DRM/Radeon
          Assignee: dri-devel at lists.freedesktop.org
          Reporter: sibradzic at gmail.com

Created attachment 115550
  --> https://bugs.freedesktop.org/attachment.cgi?id=115550&action=edit
dmesg 4.1 rc1

As soon as the radeon kms switches in from efifb, the screen goes blank for the
moment (no backlight), and then the backlight switches in, but the screen
remains black. External HDMI output works just fine. No X is involved, I can't
even see the kms console @ eDP. I can even control the backlight on the eDP
display, but all i get is the various shades of black. Fglrx works fine,
although it flickers wildly before the picture gets stable.

I've tried numerous things, like forcing EDID that was grabbed from fglrx,
disabling audio, applying all the DP training / backlight disabling patches as
in https://bugs.freedesktop.org/show_bug.cgi?id=73530, all to no avail.
Currently on linux 4.1rc1, tried 3.13, 3.16 & 3.19 as well, same issue.

Please help! I bought this laptop cause I prefer AMD, and was expecting Lenovo
to work great with Linux, but so far its broken. Ready to try some patches...

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