Christopher, you were right.
After upgrading to the PPA xorg-edgers packages, the problem seems to be solved : I can boot successfully without changing any boot parameter.
So, it looks like the problem has already been solved in nouveau.
For further reference, the PPA version number of libdrm is 2.4.20+git20100404.c7650003-0ubuntu0sarvatt3 (instead of 2.4.18-1ubuntu3)
xserver-xorg-video-nouveau version is 1:0.0.15+git20100416.40636169-0ubuntu0sarvatt instead of 1:0.0.15+git20100219+9b4118d-0ubuntu5
The fix must be between these 2 versions.
Sorry for the inconvenience, and thank you to all who had a look in this issue.
Christopher, you were right.
After upgrading to the PPA xorg-edgers packages, the problem seems to be solved : I can boot successfully without changing any boot parameter.
So, it looks like the problem has already been solved in nouveau. git20100404. c7650003- 0ubuntu0sarvatt 3 (instead of 2.4.18-1ubuntu3) xorg-video- nouveau version is 1:0.0.15+ git20100416. 40636169- 0ubuntu0sarvatt instead of 1:0.0.15+ git20100219+ 9b4118d- 0ubuntu5
For further reference, the PPA version number of libdrm is 2.4.20+
xserver-
The fix must be between these 2 versions.
Sorry for the inconvenience, and thank you to all who had a look in this issue.