Regression in i915 on 2.6.34-rc1

[Pete Zaitcev <zaitcev@redhat.com>]

Dear Dave and others:

I seem to hit a sudden regression in 2.6.34-rc1: the modeset fails.
On this box it also means, no way to start X, which is unfortunate.

Here's a quote from bad dmesg (truncated front and back for brievity):

Linux agpgart interface v0.103
agpgart-intel 0000:00:00.0: Intel HD Graphics Chipset
agpgart-intel 0000:00:00.0: detected 131068K stolen memory
agpgart-intel 0000:00:00.0: AGP aperture is 256M @ 0xd0000000
tpm_tis 00:09: 1.2 TPM (device-id 0xB, rev-id 16)
Serial: 8250/16550 driver, 4 ports, IRQ sharing enabled
................
udev: starting version 151
[drm] Initialized drm 1.1.0 20060810
i915 0000:00:02.0: PCI INT A -> GSI 16 (level, low) -> IRQ 16
i915 0000:00:02.0: setting latency timer to 64
  alloc irq_desc for 33 on node -1
  alloc kstat_irqs on node -1
i915 0000:00:02.0: irq 33 for MSI/MSI-X
[drm] set up 127M of stolen space
[drm:i915_gem_init_ringbuffer] *ERROR* Ring head not reset to zero ctl ffffffff head ffffffff tail ffffffff start ffffffff
[drm:i915_gem_init_ringbuffer] *ERROR* Ring head forced to zero ctl ffffffff head ffffffff tail ffffffff start ffffffff
[drm:i915_gem_init_ringbuffer] *ERROR* Ring initialization failed ctl ffffffff head ffffffff tail ffffffff start ffffffff
[drm:i915_driver_load] *ERROR* failed to init modeset
i915: probe of 0000:00:02.0 failed with error -5
dracut: Starting plymouth daemon

Here's old one from 2.6.33:

Linux agpgart interface v0.103
agpgart-intel 0000:00:00.0: Intel Ironlake/D Chipset
agpgart-intel 0000:00:00.0: detected 131068K stolen memory
agpgart-intel 0000:00:00.0: AGP aperture is 256M @ 0xd0000000
[drm] Initialized drm 1.1.0 20060810
Serial: 8250/16550 driver, 4 ports, IRQ sharing enabled
..........
ACPI: Power Button [PWRF]
i915 0000:00:02.0: PCI INT A -> GSI 16 (level, low) -> IRQ 16
i915 0000:00:02.0: setting latency timer to 64
i915 0000:00:02.0: irq 31 for MSI/MSI-X
[drm] set up 127M of stolen space
Console: switching to colour frame buffer device 210x65
fb0: inteldrmfb frame buffer device
registered panic notifier
[Firmware Bug]: ACPI: ACPI brightness control misses _BQC function
acpi device:1d: registered as cooling_device5
input: Video Bus as /devices/LNXSYSTM:00/LNXSYBUS:00/PNP0A08:00/LNXVIDEO:00/input/input3
ACPI: Video Device [GFX0] (multi-head: yes  rom: no  post: no)
[drm] Initialized i915 1.6.0 20080730 for 0000:00:02.0 on minor 0
dracut: Starting plymouth daemon

So... No idea what went bad, so far, sorry. I'll try to bisect
or otherwise find out. Just letting you know.

-- Pete

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