[hardy] NVIDIA driver doesn't work after upgrade from 7.10: invalid EDID checksum

Binary package hint: xorg

After upgrading to Ubuntu 8.04, the NVIDIA GeForce 8400M GS present in my Dell Inspiron 1520 laptop no longer works with the proprietary driver. This seems to be related to bug 194760 - Xorg.0.log shows that the EDID has the wrong checksum, and get-edid fails to retrieve anything.

The failure itself is odd: the screen and backlight are both active, and the session continues to load, but the screen shows a horizontally-striped pattern, which fades to a solid white screen with a thick, off-centre black bar within a few seconds. The white region of the screen repeatedly turns slowly to red and then back to white. (Switching to another virtual terminal works as expected.)

The driver fails with or without Option "IgnoreEDID" in xorg.conf, and removing the resolutions and relying on autodetection doesn't help either. The nv driver, on the other hand, works fine at the native resolution, but only if it's explicitly specified.

Here's the relevant fragment of Xorg.0.log (using parse-edid on the EDID shown here gives inaccurate power saving data, but the right resolution):

[...]
(WW) NVIDIA(GPU-0): The EDID read for display device DFP-0 is invalid: the
(WW) NVIDIA(GPU-0): checksum for EDID version 1 is invalid.
(--) NVIDIA(GPU-0):
(--) NVIDIA(GPU-0): Raw EDID bytes:
(--) NVIDIA(GPU-0):
(--) NVIDIA(GPU-0): 00 ff ff ff ff ff ff 00 4c a3 58 33 00 00 00 00
(--) NVIDIA(GPU-0): 00 11 01 03 80 21 15 78 0a 87 f5 94 57 4f 8c 27
(--) NVIDIA(GPU-0): 27 50 54 00 00 00 01 01 01 01 01 01 01 01 01 01
(--) NVIDIA(GPU-0): 01 01 01 01 01 01 4c 1d 00 90 50 20 22 30 10 30
(--) NVIDIA(GPU-0): 13 00 4b cf 10 00 00 19 00 00 00 0f 00 00 00 00
(--) NVIDIA(GPU-0): 00 00 00 00 00 23 87 02 64 00 00 00 00 fe 00 58
(--) NVIDIA(GPU-0): 55 31 30 35 04 31 35 34 58 33 0a 20 00 00 00 fe
(--) NVIDIA(GPU-0): 00 26 36 40 47 6a 8f c6 ff 01 01 0a 20 20 00 84
(--) NVIDIA(GPU-0):
(II) NVIDIA(0): NVIDIA GPU GeForce 8400M GS (G86M) at PCI:1:0:0 (GPU-0)
[...]

... and the output of get-edid:

get-edid: get-edid version 1.4.1

 Performing real mode VBE call
 Interrupt 0x10 ax=0x4f00 bx=0x0 cx=0x0
 Function supported
 Call successful

 VBE version 300
 VBE string at 0x11110 "NVIDIA"

VBE/DDC service about to be called
 Report DDC capabilities

 Performing real mode VBE call
 Interrupt 0x10 ax=0x4f15 bx=0x0 cx=0x0
 Function supported
 Call successful

 Monitor and video card combination does not support DDC1 transfers
 Monitor and video card combination does not support DDC2 transfers
 0 seconds per 128 byte EDID block transfer
 Screen is not blanked during DDC transfer

Reading next EDID block

VBE/DDC service about to be called
 Read EDID

 Performing real mode VBE call
 Interrupt 0x10 ax=0x4f15 bx=0x1 cx=0x0
 Function supported
 Call failed

The EDID data should not be trusted as the VBE call failed
Error: output block unchanged

(Running "strace get-edid" suggests that the three calls to vm86old return -1 ENOSYS, so the "call successful" messages for the first two service calls are apparently displayed in error?)

Xorg.0.log, lspci -vvnn output, and xorg.conf are attached below. "lspci -nn | grep VGA" reports "01:00.0 VGA compatible controller [0300]: nVidia Corporation GeForce 8400M GS [10de:0427] (rev a1)".