[Bug 54662] New: [bisected] Kernel 3.6 breaks KMS on Radeon RV530 (black screen)

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=54662

             Bug #: 54662
           Summary: [bisected] Kernel 3.6 breaks KMS on Radeon RV530
                    (black screen)
    Classification: Unclassified
           Product: DRI
           Version: unspecified
          Platform: x86 (IA32)
        OS/Version: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/Radeon
        AssignedTo: dri-devel at lists.freedesktop.org
        ReportedBy: skitching at apache.org


Created attachment 66826
  --> https://bugs.freedesktop.org/attachment.cgi?id=66826
Dmesg output from a kernel that does not show black screen problem

The following commit (merged in 3.6 rc series) makes the screen go black
immediately after Plymouth completes (ie just before greeter screen):

876dc9f32907e57e0298bcd0f1607cb7a2582f63 is the first bad commit
commit 876dc9f32907e57e0298bcd0f1607cb7a2582f63
Author: Christian König <deathsimple at vodafone.de>
Date:   Tue May 8 14:24:01 2012 +0200

    drm/radeon: remove radeon_fence_create

Note that this is a different bug than
https://bugs.freedesktop.org/show_bug.cgi?id=54129 (which I'm also getting) but
might be related.

The same kernel boots without problems using "nomodeset".

System is an x86-32 laptop (about 5 years old) with Radeon mobility X1600,
running Ubuntu 12.04.

lspci reports:
01:00.0 VGA compatible controller: Advanced Micro Devices [AMD] nee ATI M56P
[Radeon Mobility X1600]

Attached is full dmesg output from a *different* (ie earlier, working) kernel.
Some relevant bits include:
[    2.978637] [drm] Initialized drm 1.1.0 20060810
[    3.052940] [drm] radeon defaulting to kernel modesetting.
[    3.052945] [drm] radeon kernel modesetting enabled.
[    3.053261] [drm] initializing kernel modesetting (RV530 0x1002:0x71C5
0x103C:0x30A3).
..
[    3.245417] [drm] Loading R500 Microcode
[    3.247401] [drm] radeon: ring at 0x0000000010001000
[    3.247441] [drm] ring test succeeded in 9 usecs
...
[    4.064745] [drm] Initialized radeon 2.17.0 20080528 for 0000:01:00.0 on
minor 0

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