Commit 7f58aabc36901 causes boot hang

[George Spelvin]

Sorry for the late test; my laptop didn't need rebooting.

But when I installed a recent kernel (-rc7, actually; I just missed the
.39 release), it hung hard (no caps-lock or Alt-SysRq) partway through
boot after printing:

Linux agpgart interface v0.103
agpgart-intel 0000:00:00.0: Intel 945GM Chipset
agpgart-intel 0000:00:00.0: detected gtt size: 262144K total, 262144K mappable
agpgart-intel 0000:00:00.0: detected 8192K stolen memory
agpgart-intel 0000:00:00.0: AGP aperture is 256M @ 0xd0000000
[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
[drm] Supports vblank timestamp caching Rev 1 (10.10.2010).
[drm] Driver supports precise vblank timestamp query.
composite sync not supported
vgaarb: device changed decodes: PCI:0000:00:02.0,olddecodes=io+mem,decodes=io+mem:owns=io+mem
[drm] initialized overlay support
composite sync not supported
fbcon: inteldrmfb (fb0) is primary device
Console: switching to colour frame buffer device 180x56
fb0: inteldrmfb frame buffer device
drm: registered panic notifier
[drm] Initialized i915 1.6.0 20080730 for 0000:00:02.0 on minor 0
loop: module loaded
[drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus disabled]
[drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus disabled]
[drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus disabled]
[drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus disabled]
[drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus disabled]
[drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus disabled]
[drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus disabled]
[drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus disabled]
[drm] GMBUS timed out, falling back to bit banging on pin 4 [i915 gmbus dpc]

After some bisecting, I found that reverting 7f58aabc36901 (drm/i915:
Reset GMBUS controller after NAK) resulted in a successful boot, which
replaced the above hang with:

[drm] Initialized i915 1.6.0 20080730 for 0000:00:02.0 on minor 0
loop: module loaded
[drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus disabled]
[drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus disabled]
[drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus disabled]
[drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus disabled]
[drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus disabled]
[drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus disabled]
[drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus disabled]
[drm] GMBUS timed out, falling back to bit banging on pin 0 [i915 gmbus disabled]
ata_piix 0000:00:1f.2: version 2.13
ata_piix 0000:00:1f.2: PCI INT B -> GSI 17 (level, low) -> IRQ 17
ata_piix 0000:00:1f.2: MAP [ P0 P2 IDE IDE ]
ata_piix 0000:00:1f.2: setting latency timer to 64
scsi0 : ata_piix
scsi1 : ata_piix
ata1: SATA max UDMA/133 cmd 0x1f0 ctl 0x3f6 bmdma 0xbfa0 irq 14
ata2: PATA max UDMA/100 cmd 0x170 ctl 0x376 bmdma 0xbfa8 irq 15
b44 0000:02:00.0: PCI INT A -> GSI 17 (level, low) -> IRQ 17
[etc...]

The PCI devices on this laptop (Dell Inspirion E1405) are:

00:00.0 Host bridge [0600]: Intel Corporation Mobile 945GM/PM/GMS, 943/940GML and 945GT Express Memory Controller Hub [8086:27a0] (rev 03)
00:02.0 VGA compatible controller [0300]: Intel Corporation Mobile 945GM/GMS, 943/940GML Express Integrated Graphics Controller [8086:27a2] (rev 03)
00:02.1 Display controller [0380]: Intel Corporation Mobile 945GM/GMS/GME, 943/940GML Express Integrated Graphics Controller [8086:27a6] (rev 03)
00:1b.0 Audio device [0403]: Intel Corporation N10/ICH 7 Family High Definition Audio Controller [8086:27d8] (rev 01)
00:1c.0 PCI bridge [0604]: Intel Corporation N10/ICH 7 Family PCI Express Port 1 [8086:27d0] (rev 01)
00:1c.1 PCI bridge [0604]: Intel Corporation N10/ICH 7 Family PCI Express Port 2 [8086:27d2] (rev 01)
00:1c.3 PCI bridge [0604]: Intel Corporation N10/ICH 7 Family PCI Express Port 4 [8086:27d6] (rev 01)
00:1d.0 USB Controller [0c03]: Intel Corporation N10/ICH 7 Family USB UHCI Controller #1 [8086:27c8] (rev 01)
00:1d.1 USB Controller [0c03]: Intel Corporation N10/ICH 7 Family USB UHCI Controller #2 [8086:27c9] (rev 01)
00:1d.2 USB Controller [0c03]: Intel Corporation N10/ICH 7 Family USB UHCI Controller #3 [8086:27ca] (rev 01)
00:1d.3 USB Controller [0c03]: Intel Corporation N10/ICH 7 Family USB UHCI Controller #4 [8086:27cb] (rev 01)
00:1d.7 USB Controller [0c03]: Intel Corporation N10/ICH 7 Family USB2 EHCI Controller [8086:27cc] (rev 01)
00:1e.0 PCI bridge [0604]: Intel Corporation 82801 Mobile PCI Bridge [8086:2448] (rev e1)
00:1f.0 ISA bridge [0601]: Intel Corporation 82801GBM (ICH7-M) LPC Interface Bridge [8086:27b9] (rev 01)
00:1f.2 IDE interface [0101]: Intel Corporation 82801GBM/GHM (ICH7 Family) SATA IDE Controller [8086:27c4] (rev 01)
00:1f.3 SMBus [0c05]: Intel Corporation N10/ICH 7 Family SMBus Controller [8086:27da] (rev 01)
02:00.0 Ethernet controller [0200]: Broadcom Corporation BCM4401-B0 100Base-TX [14e4:170c] (rev 02)
02:01.0 FireWire (IEEE 1394) [0c00]: Ricoh Co Ltd R5C832 IEEE 1394 Controller [1180:0832]
02:01.1 SD Host controller [0805]: Ricoh Co Ltd R5C822 SD/SDIO/MMC/MS/MSPro Host Adapter [1180:0822] (rev 19)
02:01.2 System peripheral [0880]: Ricoh Co Ltd R5C843 MMC Host Controller [1180:0843] (rev 01)
02:01.3 System peripheral [0880]: Ricoh Co Ltd R5C592 Memory Stick Bus Host Adapter [1180:0592] (rev 0a)
02:01.4 System peripheral [0880]: Ricoh Co Ltd xD-Picture Card Controller [1180:0852] (rev 05)
0c:00.0 Network controller [0280]: Broadcom Corporation BCM4321 802.11a/b/g/n [14e4:4328] (rev 01)

The kernel is dual-processor 32-bit.

Sorry for the bad news.