Thanks. At first glance it appears that you still have kernel modesetting enabled...
... despite booting with modeset=0 (is this maybe the wrong syntax for current drivers ?)...
... and you're using the fbdev X driver rather than radeon (-ati)...
[ 15.105271] [drm] radeon kernel modesetting enabled.
[ 15.105454] radeon 0000:01:05.0: power state changed by ACPI to D0
[ 15.105461] radeon 0000:01:05.0: power state changed by ACPI to D0
[ 15.106056] ACPI: PCI Interrupt Link [LNK0] enabled at IRQ 10
[ 15.112590] [drm] initializing kernel modesetting (RS200 0x1002:0x4337 0x103C:0x0850).
[ 15.112638] [drm] register mmio base: 0xC0300000
[ 15.112641] [drm] register mmio size: 65536
[ 15.113036] agpgart-ati 0000:00:00.0: AGP 2.0 bridge
[ 15.113060] agpgart-ati 0000:00:00.0: putting AGP V2 device into 4x mode
[ 15.113110] radeon 0000:01:05.0: putting AGP V2 device into 4x mode
[ 15.113117] radeon 0000:01:05.0: GTT: 64M 0xC4000000 - 0xC7FFFFFF
[ 15.113126] radeon 0000:01:05.0: VRAM: 128M 0x0000000038000000 - 0x000000003FFFFFFF (128M used)
[ 15.113140] [drm] Supports vblank timestamp caching Rev 1 (10.10.2010).
[ 15.113144] [drm] Driver supports precise vblank timestamp query.
[ 15.113166] [drm] radeon: irq initialized.
[ 15.116172] [drm] Detected VRAM RAM=128M, BAR=256M
[ 15.116177] [drm] RAM width 64bits DDR
[ 15.118158] [TTM] Zone kernel: Available graphics memory: 445888 kiB
[ 15.118164] [TTM] Zone highmem: Available graphics memory: 449700 kiB
[ 15.118167] [TTM] Initializing pool allocator
[ 15.118228] [drm] radeon: 128M of VRAM memory ready
[ 15.118232] [drm] radeon: 64M of GTT memory ready.
[ 15.118273] [drm] radeon: ib pool ready.
[ 15.141641] radeon 0000:01:05.0: WB disabled
[ 15.141654] [drm] fence driver on ring 0 use gpu addr 0xc4000000 and cpu addr 0xf8024000
[ 15.141816] [drm] Loading R100 Microcode
[ 15.105454] radeon 0000:01:05.0: power state changed by ACPI to D0
[ 15.105461] radeon 0000:01:05.0: power state changed by ACPI to D0
[ 15.106056] ACPI: PCI Interrupt Link [LNK0] enabled at IRQ 10
[ 15.112590] [drm] initializing kernel modesetting (RS200 0x1002:0x4337 0x103C:0x0850).
[ 15.112638] [drm] register mmio base: 0xC0300000
[ 15.112641] [drm] register mmio size: 65536
[ 15.113036] agpgart-ati 0000:00:00.0: AGP 2.0 bridge
[ 15.113060] agpgart-ati 0000:00:00.0: putting AGP V2 device into 4x mode
[ 15.113110] radeon 0000:01:05.0: putting AGP V2 device into 4x mode
[ 15.113117] radeon 0000:01:05.0: GTT: 64M 0xC4000000 - 0xC7FFFFFF
[ 15.113126] radeon 0000:01:05.0: VRAM: 128M 0x0000000038000000 - 0x000000003FFFFFFF (128M used)
[ 15.113140] [drm] Supports vblank timestamp caching Rev 1 (10.10.2010).
[ 15.113144] [drm] Driver supports precise vblank timestamp query.
[ 15.113166] [drm] radeon: irq initialized.
[ 15.116172] [drm] Detected VRAM RAM=128M, BAR=256M
[ 15.116177] [drm] RAM width 64bits DDR
[ 15.118158] [TTM] Zone kernel: Available graphics memory: 445888 kiB
[ 15.118164] [TTM] Zone highmem: Available graphics memory: 449700 kiB
[ 15.118167] [TTM] Initializing pool allocator
[ 15.118228] [drm] radeon: 128M of VRAM memory ready
[ 15.118232] [drm] radeon: 64M of GTT memory ready.
[ 15.118273] [drm] radeon: ib pool ready.
[ 15.141641] radeon 0000:01:05.0: WB disabled
[ 15.141654] [drm] fence driver on ring 0 use gpu addr 0xc4000000 and cpu addr 0xf8024000
[ 15.141816] [drm] Loading R100 Microcode
[ 425.714] Current Operating System: Linux Microknoppix 3.4.9 #34 SMP PREEMPT Fri Aug 17 06:30:04 CEST 2012 i686
[ 425.714] Kernel command line: ramdisk_size=100000 lang=en apm=power-off initrd=minirt.gz nomce libata.force=noncq hpsa.hpsa_allow_any=1 loglevel=1 tz=localtime BOOT_IMAGE=linux radeon.modeset=0
[ 425.714] Kernel command line: ramdisk_size=100000 lang=en apm=power-off initrd=minirt.gz nomce libata.force=noncq hpsa.hpsa_allow_any=1 loglevel=1 tz=localtime BOOT_IMAGE=linux radeon.modeset=0
[ 425.725] (II) Loading /usr/lib/xorg/modules/drivers/fbdev_drv.so
[ 425.725] (II) Module fbdev: vendor="X.Org Foundation"
[ 425.725] compiled for 1.12.1, module version = 0.4.2
[ 425.725] ABI class: X.Org Video Driver, version 12.0
[ 425.725] (II) FBDEV: driver for framebuffer: fbdev
[ 425.725] (++) using VT number 5
[ 425.746] (II) Loading sub module "fbdevhw"
[ 425.746] (II) LoadModule: "fbdevhw"
[ 425.746] (II) Loading /usr/lib/xorg/modules/libfbdevhw.so
[ 425.747] (II) Module fbdevhw: vendor="X.Org Foundation"
[ 425.747] compiled for 1.12.3, module version = 0.0.2
[ 425.747] ABI class: X.Org Video Driver, version 12.0
[ 425.747] (**) FBDEV(0): claimed PCI slot 1@0:5:0
[ 425.747] (II) FBDEV(0): using default device
[ 425.747] (==) FBDEV(0): Depth 24, (==) framebuffer bpp 32
[ 425.747] (==) FBDEV(0): RGB weight 888
[ 425.747] (==) FBDEV(0): Default visual is TrueColor
[ 425.747] (==) FBDEV(0): Using gamma correction (1.0, 1.0, 1.0)
[ 425.747] (II) FBDEV(0): hardware: radeondrmfb (video memory: 3072kB)
[ 425.747] (II) FBDEV(0): checking modes against framebuffer device...
[ 425.747] (II) FBDEV(0): checking modes against monitor...
[ 425.747] (--) FBDEV(0): Virtual size is 1024x768 (pitch 1024)
[ 425.747] (**) FBDEV(0): Built-in mode "current"
[ 425.747] (++) FBDEV(0): DPI set to (96, 96)
[ 425.747] (II) Loading sub module "fb"
[ 425.747] (II) LoadModule: "fb"
[ 425.748] (II) Loading /usr/lib/xorg/modules/libfb.so
[ 425.748] (II) Module fb: vendor="X.Org Foundation"
[ 425.748] compiled for 1.12.3, module version = 1.0.0
[ 425.748] ABI class: X.Org ANSI C Emulation, version 0.4
[ 425.748] (**) FBDEV(0): using shadow framebuffer
[ 425.748] (II) Loading sub module "shadow"
[ 425.748] (II) LoadModule: "shadow"
[ 425.750] (II) Loading /usr/lib/xorg/modules/libshadow.so
[ 425.756] (II) Module shadow: vendor="X.Org Foundation"
[ 425.757] compiled for 1.12.3, module version = 1.1.0
[ 425.757] ABI class: X.Org ANSI C Emulation, version 0.4
[ 425.757] (==) Depth 24 pixmap format is 32 bpp
[ 425.838] (==) FBDEV(0): Backing store disabled
[ 425.839] (EE) FBDEV(0): FBIOPUTCMAP: Invalid argument
[ 425.839] (EE) FBDEV(0): FBIOPUTCMAP: Invalid argument
[ 425.839] (EE) FBDEV(0): FBIOPUTCMAP: Invalid argument
[ 425.839] (EE) FBDEV(0): FBIOPUTCMAP: Invalid argument
[ 425.839] (EE) FBDEV(0): FBIOPUTCMAP: Invalid argument
[ 425.725] (II) Module fbdev: vendor="X.Org Foundation"
[ 425.725] compiled for 1.12.1, module version = 0.4.2
[ 425.725] ABI class: X.Org Video Driver, version 12.0
[ 425.725] (II) FBDEV: driver for framebuffer: fbdev
[ 425.725] (++) using VT number 5
[ 425.746] (II) Loading sub module "fbdevhw"
[ 425.746] (II) LoadModule: "fbdevhw"
[ 425.746] (II) Loading /usr/lib/xorg/modules/libfbdevhw.so
[ 425.747] (II) Module fbdevhw: vendor="X.Org Foundation"
[ 425.747] compiled for 1.12.3, module version = 0.0.2
[ 425.747] ABI class: X.Org Video Driver, version 12.0
[ 425.747] (**) FBDEV(0): claimed PCI slot 1@0:5:0
[ 425.747] (II) FBDEV(0): using default device
[ 425.747] (==) FBDEV(0): Depth 24, (==) framebuffer bpp 32
[ 425.747] (==) FBDEV(0): RGB weight 888
[ 425.747] (==) FBDEV(0): Default visual is TrueColor
[ 425.747] (==) FBDEV(0): Using gamma correction (1.0, 1.0, 1.0)
[ 425.747] (II) FBDEV(0): hardware: radeondrmfb (video memory: 3072kB)
[ 425.747] (II) FBDEV(0): checking modes against framebuffer device...
[ 425.747] (II) FBDEV(0): checking modes against monitor...
[ 425.747] (--) FBDEV(0): Virtual size is 1024x768 (pitch 1024)
[ 425.747] (**) FBDEV(0): Built-in mode "current"
[ 425.747] (++) FBDEV(0): DPI set to (96, 96)
[ 425.747] (II) Loading sub module "fb"
[ 425.747] (II) LoadModule: "fb"
[ 425.748] (II) Loading /usr/lib/xorg/modules/libfb.so
[ 425.748] (II) Module fb: vendor="X.Org Foundation"
[ 425.748] compiled for 1.12.3, module version = 1.0.0
[ 425.748] ABI class: X.Org ANSI C Emulation, version 0.4
[ 425.748] (**) FBDEV(0): using shadow framebuffer
[ 425.748] (II) Loading sub module "shadow"
[ 425.748] (II) LoadModule: "shadow"
[ 425.750] (II) Loading /usr/lib/xorg/modules/libshadow.so
[ 425.756] (II) Module shadow: vendor="X.Org Foundation"
[ 425.757] compiled for 1.12.3, module version = 1.1.0
[ 425.757] ABI class: X.Org ANSI C Emulation, version 0.4
[ 425.757] (==) Depth 24 pixmap format is 32 bpp
[ 425.838] (==) FBDEV(0): Backing store disabled
[ 425.839] (EE) FBDEV(0): FBIOPUTCMAP: Invalid argument
[ 425.839] (EE) FBDEV(0): FBIOPUTCMAP: Invalid argument
[ 425.839] (EE) FBDEV(0): FBIOPUTCMAP: Invalid argument
[ 425.839] (EE) FBDEV(0): FBIOPUTCMAP: Invalid argument
[ 425.839] (EE) FBDEV(0): FBIOPUTCMAP: Invalid argument
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