[9front] igfx on haswell

[qwx@sciops.net]

Hello,

I recently acquired an x240 and upgraded it with some
x250 parts, and I noticed that igfx now magically works
on it.  Previous reports suggested that the only
haswell machines on which igfx worked were the two I
had worked with in the past.  Everything was configured
correctly according to both the spec and the values of
the card's registers, but screens remained blank, and
short of blind guessing games and trial and error, I
couldn't do much debugging without the hardware at hand.
Since broadwell is not very different from haswell, it's
possible that it works there as well without modification.

It would be great if anyone with haswell (*40 thinkpads)
or broadwell (*50 thinkpads) could try to test if it
works for them as well.  eDP (internal display), DP
and HDMI/DVI could/should work, as they do for me.  Note
that haswell VGA is still unimplemented.

The steps necessary are adding the PCI did (use pci(8))
to /lib/vgadb under the igfx ctrl entry, and
/sys/src/cmd/aux/vga/igfx.c:/^devtype if it's not
there already, and either booting with monitor=auto in
plan9.ini, or calling vga(8) eg.:

	; aux/vga -m auto -l $vgasize

If things worked correctly, you will see a picture,
otherwise the screen will remain blank.

Setups that require more than just automatic
configuration would be more painful.  You could either
refer to [1] or ask here, but please don't waste too
much time :)

Thanks!

Cheers,
qwx

[1] http://nopenopenope.net/posts/igfx