> you can dump the register contents with aux/vga and compare
> native igfx vs vesa + igfx.
> 
> this will only catch register differences that igfx knows
> about tho.

I did this, and the vga dump of aux/vga -l 1680x1050x32 for
bare igfx device is attached.
The diff of
#term diff (igfx on vesa dump) (bare igfx)
is as follows:
I don't see any serious problems...
In case bare igfx, monitor=s2231wA is defined, in the the other
not.
--------from here-----
5c5
< vga sequencer        03 21 0F 00 0E
---
> vga sequencer        03 00 03 00 02
8c8
< vga graphics         00 00 00 00 00 00 05 0F - FF
---
> vga graphics         00 00 00 00 00 10 0E 00 - FF
15c15
< igfx pipe a src      [0006001c] = 03ff02ff
---
> igfx pipe a src      [0006001c] = 027f01df
21,26c21,26
< igfx pipe a ht       [00060000] = 053f03ff
< igfx pipe a hb       [00060004] = 053f03ff
< igfx pipe a hs       [00060008] = 049f0417
< igfx pipe a vt       [0006000c] = 032502ff
< igfx pipe a vb       [00060010] = 032502ff
< igfx pipe a vs       [00060014] = 03080302
---
> igfx pipe a ht       [00060000] = 031f027f
> igfx pipe a hb       [00060004] = 03170287
> igfx pipe a hs       [00060008] = 02ef028f
> igfx pipe a vt       [0006000c] = 020c01df
> igfx pipe a vb       [00060010] = 020401e7
> igfx pipe a vs       [00060014] = 01eb01e9
28c28
< igfx dsp a cntr      [00070180] = c8000000
---
> igfx dsp a cntr      [00070180] = 48000000
30c30
< igfx dsp a stride    [00070188] = 00000400
---
> igfx dsp a stride    [00070188] = 00000280
57,58c57,58
< igfx dpll a ctrl     [00006014] = 94040c00
< igfx dpll a fp0      [00006040] = 00041505
---
> igfx dpll a ctrl     [00006014] = 84800c00
> igfx dpll a fp0      [00006040] = 00031108
60c60
< igfx dpll a ctrl p1  3
---
> igfx dpll a ctrl p1  8
62,64c62,64
< igfx dpll a fp0 m1   21
< igfx dpll a fp0 m2   5
< igfx dpll a fp0 n    4
---
> igfx dpll a fp0 m1   17
> igfx dpll a fp0 m2   8
> igfx dpll a fp0 n    3
66c66
< igfx dpll a fp0 freq 65066666
---
> igfx dpll a fp0 freq 25200000
80c80
< igfx adpa            [00061100] = 80000000
---
> igfx adpa            [00061100] = 80008000
84c84
< igfx vgacntrl        [00071400] = 8000008e
---
> igfx vgacntrl        [00071400] = 0000008e
160c160
< type=igfx, size=1680x1050x32
---
> type=s2231wA, size=1680x1050x32
167d166
< mode->attr: display=1
229c228
< igfx dpll a ctrl     [00006014] = 94010c00
---
> igfx dpll a ctrl     [00006014] = 94010c01
231c230
< igfx dpll a fp1      [00006044] = 00031108
---
> igfx dpll a fp1      [00006044] = 00061505
332c331
< type=igfx, size=1680x1050x32
---
> type=s2231wA, size=1680x1050x32
339d337
< mode->attr: display=1
402c400
< igfx dpll a ctrl     [00006014] = 94010c00
---
> igfx dpll a ctrl     [00006014] = 94010c01
404c402
< igfx dpll a fp1      [00006044] = 00031108
---
> igfx dpll a fp1      [00006044] = 00061505
diff 495: some
---- to here----

Kenji