nouveau: NVIDIA GeForce 6800 works well in DVI but not in VGA

[Frédéric Fauberteau <triaxx%NetBSD.org@localhost>]

Hi,

Thanks for the work on nouveau that works fine for me now.

I have just a glitch (diagonal noise of dotted line) when the card is 
plugged through VGA cable.

I would identify the problem but I have no idea where and how to start 
investigation. Any help would be gratefully appreciated.

# pcictl /dev/pci0 list | grep NVIDIA
001:00:0: NVIDIA GeForce 6800 (VGA display, revision 0xa1)

[   1.0000000] NetBSD 8.99.29 (DEBUG) #0: Sat Dec 29 14:12:14 UTC 2018
[   1.0000000]  root@lurker:/usr/obj/sys/arch/i386/compile/DEBUG
[...]
[   1.0074185] nouveau0 at pci1 dev 0 function 0: vendor 10de product 
0041 (rev. 0xa1)
[   1.0074185] nouveau0: info: NVIDIA NV40 (440100a1)