At boot, the screen goes blank.  This happens at the moment when the screen
would normally change from VGA text console to framebuffer text console.  I
can't make an ssh connection to the box after screen goes blank.

Motherboard: MSI K9AGM3
Video card: Radeon HD 6670

lspci -vvv gives: 

01:00.0 VGA compatible controller: Advanced Micro Devices [AMD] nee ATI Turks [Radeon HD 6670] (prog-if 00 [VGA controller])
        Subsystem: ASUSTeK Computer Inc. Device 03e0
        Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR+ FastB2B- DisINTx+
        Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
        Latency: 0, Cache Line Size: 64 bytes
        Interrupt: pin A routed to IRQ 43
        Region 0: Memory at d0000000 (64-bit, prefetchable) [size=256M]
        Region 2: Memory at fe9e0000 (64-bit, non-prefetchable) [size=128K]
        Region 4: I/O ports at c000 [size=256]
        Expansion ROM at fe9c0000 [disabled] [size=128K]
        Capabilities: <access denied>
        Kernel driver in use: radeon

I bisected this.  The first bad commit is:
0ecebb9e0d14e9948e0b1529883a776758117d6f drm/radeon: switch to a finer grained reset for evergreen

Reverting this commit on top of v3.8-rc4 results in a working system.