Ok, I included /sys/src/cmd/aux/vga/jgfx.c and /sys/src/9/pc/vgaigfx.c.
Many pesonal comments, though some of them might be my miss-understasnding.
If so, please forget them.
Many A<<0xFF like lines might not be neccessary, however, some of them
are definitely important.

Present patch isn't aimed to use for DP connector, because I have
no DP input monitor here.  I tried DP->HDMI connector, but failed.
I have no motivation for it, sorry.

my /cfg/pxe/XXXXXX is as follows:
#Core-i5 Dell Optiflex 790 desktop (Sandy-bridge)
bootargs=tcp
bootfile=/386/9pcf
nobootprompt=tcp
mouseport=usb
monitor=E1780SD
display=1
vgasize=1280x1024x32

Kenji

PS. this mail is written on the new sandy-bridge machine, and
posted its sysinfo to the 9front's web site.