Foi um erro do kernel. Para esta versão do kernel, uma linha nos drivers radeon KMS precisa ser ajustada e o kernel reconstruído. A maior parte disso é discutível, porque é corrigido em versões mais recentes do kernel.
Meu computador inicializou sob o Debian Wheezy (kernel 3.2) sem nenhum problema gráfico. Após atualizar para sid (3.10 kernel), a tela fica preta (ou seja, o display pisca um pouco e entra no modo de economia de energia) e desativa sempre que o kernel tenta configurar o framade buffer (ambos se eu inicializar sem a opção nomodeset e se eu carregar o módulo via modprobe radeon modeset=1 ). Eu então compilei o kernel (ambos 3.10 e 3.11), Mesa e o driver xorg para mim com os mesmos resultados.
lspci -s 01:05.0 -vv :
01:05.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] RS880 [Radeon HD 4250] (prog-if 00 [VGA controller])
Subsystem: ASRock Incorporation Device 9715
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 18
Region 0: Memory at d0000000 (32-bit, prefetchable) [size=256M]
Region 1: I/O ports at d000 [size=256]
Region 2: Memory at febf0000 (32-bit, non-prefetchable) [size=64K]
Region 5: Memory at fea00000 (32-bit, non-prefetchable) [size=1M]
Expansion ROM at <unassigned> [disabled]
Capabilities: [50] Power Management version 3
Flags: PMEClk- DSI- D1+ D2+ AuxCurrent=0mA PME(D0-,D1-,D2-,D3hot-,D3cold-)
Status: D0 NoSoftRst- PME-Enable- DSel=0 DScale=0 PME-
Capabilities: [a0] MSI: Enable- Count=1/1 Maskable- 64bit+
Address: 0000000000000000 Data: 0000
Kernel driver in use: radeon
dmesg | grep -i 'drm|radeon' :
[ 6.995487] [drm] Initialized drm 1.1.0 20060810
[ 7.744080] [drm] VGACON disable radeon kernel modesetting.
[ 7.744125] [drm:radeon_init] *ERROR* No UMS support in radeon module!
[ 395.010450] [drm] radeon kernel modesetting enabled.
[ 395.010779] [drm] initializing kernel modesetting (RS880 0x1002:0x9715 0x1849:0x9715).
[ 395.010828] [drm] register mmio base: 0xFEBF0000
[ 395.010859] [drm] register mmio size: 65536
[ 395.015827] radeon 0000:01:05.0: VRAM: 512M 0x00000000C0000000 - 0x00000000DFFFFFFF (512M used)
[ 395.015863] radeon 0000:01:05.0: GTT: 512M 0x00000000A0000000 - 0x00000000BFFFFFFF
[ 395.015898] [drm] Detected VRAM RAM=512M, BAR=256M
[ 395.015930] [drm] RAM width 32bits DDR
[ 395.016192] [drm] radeon: 512M of VRAM memory ready
[ 395.016223] [drm] radeon: 512M of GTT memory ready.
[ 395.016261] [drm] GART: num cpu pages 131072, num gpu pages 131072
[ 395.030829] [drm] Loading RS780 Microcode
[ 395.085860] [drm] PCIE GART of 512M enabled (table at 0x00000000C0040000).
[ 395.085978] radeon 0000:01:05.0: WB enabled
[ 395.086019] radeon 0000:01:05.0: fence driver on ring 0 use gpu addr 0x00000000a0000c00 and cpu addr 0xffff8801f7aacc00
[ 395.086065] radeon 0000:01:05.0: fence driver on ring 3 use gpu addr 0x00000000a0000c0c and cpu addr 0xffff8801f7aacc0c
[ 395.086109] [drm] Supports vblank timestamp caching Rev 1 (10.10.2010).
[ 395.086147] [drm] Driver supports precise vblank timestamp query.
[ 395.086201] [drm] radeon: irq initialized.
[ 395.086502] radeon 0000:01:05.0: setting latency timer to 64
[ 395.118357] [drm] ring test on 0 succeeded in 0 usecs
[ 395.118455] [drm] ring test on 3 succeeded in 1 usecs
[ 395.118664] [drm] ib test on ring 0 succeeded in 0 usecs
[ 395.118716] [drm] ib test on ring 3 succeeded in 0 usecs
[ 395.119245] [drm] Radeon Display Connectors
[ 395.119283] [drm] Connector 0:
[ 395.119319] [drm] VGA-1
[ 395.119357] [drm] DDC: 0x7e40 0x7e40 0x7e44 0x7e44 0x7e48 0x7e48 0x7e4c 0x7e4c
[ 395.119397] [drm] Encoders:
[ 395.119433] [drm] CRT1: INTERNAL_KLDSCP_DAC1
[ 395.119470] [drm] Connector 1:
[ 395.119505] [drm] HDMI-A-1
[ 395.119540] [drm] HPD3
[ 395.119577] [drm] DDC: 0x7e50 0x7e50 0x7e54 0x7e54 0x7e58 0x7e58 0x7e5c 0x7e5c
[ 395.119617] [drm] Encoders:
[ 395.119652] [drm] DFP3: INTERNAL_KLDSCP_LVTMA
[ 395.119715] [drm] radeon: power management initialized
[ 395.183376] [drm] fb mappable at 0xD0142000
[ 395.183417] [drm] vram apper at 0xD0000000
[ 395.184903] [drm] size 9216000
[ 395.184939] [drm] fb depth is 24
[ 395.184975] [drm] pitch is 7680
[ 395.185145] fbcon: radeondrmfb (fb0) is primary device
[ 395.380720] radeon 0000:01:05.0: fb0: radeondrmfb frame buffer device
[ 395.380813] radeon 0000:01:05.0: registered panic notifier
[ 395.381119] [drm] Initialized radeon 2.34.0 20080528 for 0000:01:05.0 on minor 0
Meu Xorg.log está aqui: link