I finally found some time to revive one of my old laptops with NetBSD after some service testing other stuff. IT is a ThinkPAD T61p with NVidia graphics. I had a live system image prepared a few months ago which I could use to compile -current from scratch and subsequently sysupdate. This was 7.99.42 from 20/11/2016 or so, which worked perfectly, including Xorg. The relevant bits from the dmesg follow:
pci1: i/o space, memory space enabled, rd/line, wr/inv ok
nouveau0 at pci1 dev 0 function 0: vendor 10de product 040c (rev. 0xa1)
drm kern info: nouveau [ DEVICE][nouveau0] BOOT0 : 0x084c00a2
drm kern info: nouveau [ DEVICE][nouveau0] Chipset: G84 (NV84)
drm kern info: nouveau [ DEVICE][nouveau0] Family : NV50
drm kern info: nouveau [ VBIOS][nouveau0] checking PRAMIN for image...
drm kern info: nouveau [ VBIOS][nouveau0] ... appears to be valid
drm kern info: nouveau [ VBIOS][nouveau0] using image from PRAMIN
drm kern info: nouveau [ VBIOS][nouveau0] BIT signature found
drm kern info: nouveau [ VBIOS][nouveau0] version 60.84.51.00.00
drm kern info: nouveau [ PFB][nouveau0] RAM type: GDDR3
drm kern info: nouveau [ PFB][nouveau0] RAM size: 256 MiB
drm kern info: nouveau [ PFB][nouveau0] ZCOMP: 1892 tags
drm kern info: nouveau [ VOLT][nouveau0] GPU voltage: 1150000uv
drm kern info: nouveau [ PTHERM][nouveau0] FAN control: none / external
drm kern info: nouveau [ PTHERM][nouveau0] fan management: automatic
drm kern info: nouveau [ PTHERM][nouveau0] internal sensor: yes
drm kern info: nouveau [ CLK][nouveau0] 20: core 169 MHz shader 338 MHz memory 100 MHz
drm kern info: nouveau [ CLK][nouveau0] 21: core 275 MHz shader 550 MHz memory 301 MHz
drm kern info: nouveau [ CLK][nouveau0] 22: core 475 MHz shader 950 MHz memory 702 MHz
drm kern info: nouveau [ CLK][nouveau0] --: core 275 MHz shader 550 MHz memory 302 MHz
Zone kernel: Available graphics memory: 2839100 kiB
Zone dma32: Available graphics memory: 2097152 kiB
drm kern info: nouveau [ DRM] VRAM: 256 MiB
drm kern info: nouveau [ DRM] GART: 1048576 MiB
drm kern info: nouveau [ DRM] TMDS table version 2.0
drm kern info: nouveau [ DRM] DCB version 4.0
drm kern info: nouveau [ DRM] DCB outp 00: 01000323 00010034
drm kern info: nouveau [ DRM] DCB outp 01: 02811300 00000028
drm kern info: nouveau [ DRM] DCB outp 02: 02822312 00010030
drm kern info: nouveau [ DRM] DCB conn 00: 0040
drm kern info: nouveau [ DRM] DCB conn 01: 0100
drm kern info: nouveau [ DRM] DCB conn 02: 1231
drm: Supports vblank timestamp caching Rev 2 (21.10.2013).
drm: Driver supports precise vblank timestamp query.
drm kern info: nouveau [ DRM] MM: using CRYPT for buffer copies
nouveaufb0 at nouveau0
nouveau0: info: registered panic notifier
nouveaufb0: framebuffer at 0xffff8000919a2000, size 1920x1200, depth 32, stride 7680
wsdisplay0 at nouveaufb0 kbdmux 1: console (default, vt100 emulation), using wskbd0
wsmux1: connecting to wsdisplay0
....
drm kern error: nouveau E[ PDISP][nouveau0] INVALID_STATE [UNK0B] chid 1 mthd 0x0080 data 0x00000000
drm kern error: nouveau E[ PDISP][nouveau0] Base 0:
drm kern error: nouveau E[ PDISP][nouveau0] 0x0084: 0x00000000
drm kern error: nouveau E[ PDISP][nouveau0] 0x0088: 0x00000000
drm kern error: nouveau E[ PDISP][nouveau0] 0x008c: 0x00000000
drm kern error: nouveau E[ PDISP][nouveau0] 0x0090: 0x00000000
drm kern error: nouveau E[ PDISP][nouveau0] 0x0094: 0x00000000 -> 0xcafe0000
drm kern error: nouveau E[ PDISP][nouveau0] 0x00a0: 0x00000000
drm kern error: nouveau E[ PDISP][nouveau0] 0x00a4: 0x00000000
drm kern error: nouveau E[ PDISP][nouveau0] 0x00c0: 0x00000000 -> 0x01000003
drm kern error: nouveau E[ PDISP][nouveau0] 0x00c4: 0x00000000
drm kern error: nouveau E[ PDISP][nouveau0] 0x00c8: 0x00000000
drm kern error: nouveau E[ PDISP][nouveau0] 0x00cc: 0x00000000
drm kern error: nouveau E[ PDISP][nouveau0] 0x00e0: 0x00000000 -> 0x40000000
drm kern error: nouveau E[ PDISP][nouveau0] 0x00e4: 0x00000000
drm kern error: nouveau E[ PDISP][nouveau0] 0x00e8: 0x00000000
drm kern error: nouveau E[ PDISP][nouveau0] 0x00ec: 0x00000000
drm kern error: nouveau E[ PDISP][nouveau0] 0x00fc: 0x00000000
drm kern error: nouveau E[ PDISP][nouveau0] 0x0100: 0xfffe0000
drm kern error: nouveau E[ PDISP][nouveau0] 0x0104: 0x00000000
drm kern error: nouveau E[ PDISP][nouveau0] 0x0110: 0x00000000
drm kern error: nouveau E[ PDISP][nouveau0] 0x0114: 0x00000000
drm kern error: nouveau E[ PDISP][nouveau0] Base 0 - Image 0:
drm kern error: nouveau E[ PDISP][nouveau0] 0x0800: 0x00000000 -> 0x00000700
drm kern error: nouveau E[ PDISP][nouveau0] 0x0804: 0x00000000
drm kern error: nouveau E[ PDISP][nouveau0] 0x0808: 0x00000000 -> 0x04b00780
drm kern error: nouveau E[ PDISP][nouveau0] 0x080c: 0x00000000 -> 0x00101e00
drm kern error: nouveau E[ PDISP][nouveau0] 0x0810: 0x0000e900 -> 0x0000cf00
drm kern error: nouveau E[ PDISP][nouveau0] Base 0 - Image 1:
drm kern error: nouveau E[ PDISP][nouveau0] 0x0c00: 0x00000000 -> 0x00000700
drm kern error: nouveau E[ PDISP][nouveau0] 0x0c04: 0x00000000
drm kern error: nouveau E[ PDISP][nouveau0] 0x0c08: 0x00000000 -> 0x04b00780
drm kern error: nouveau E[ PDISP][nouveau0] 0x0c0c: 0x00000000 -> 0x00101e00
drm kern error: nouveau E[ PDISP][nouveau0] 0x0c10: 0x0000e900 -> 0x0000cf00
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I then did a full release build on this machine ( it is only a dual core -Core 2 Duo 2.2Ghz CPU - so it took some time ) and performed sysupgrade. The resulting system works also fine, with the unfortunate exception that the screen stays dark after the framebuffer line in the dmesg is seen, when it has to switch to high resolution mode during bootstrap. The boot completes without a problem, I am able to ssh to the laptop and monitor what is going on, I can also blindly logon the laptop's console and run 'startx', which I see in the ssh window from elsewhere is running correctly.
The same behaviour is shown when I installed - again using sysupdate - 8BETA from today, the screen remains black.
If I compare the dmesg.boot files from the three versions - 7.99.42 - working - 8BETA and 8.99.1 not working - the only apparently relevant difference I can see is:
I.e. on the working system the framebuffer address is different from the address on the two not working ones - which are the same.
It would be a bit tedious to do bisecting from 20th of November until now, so I hoped someone would remember some change for this.