drm MSI support

[Robert Noland]

I would like to get some initial feedback on this patch.  It enables MSI
on capable cards.  (I'm using it on my i965gm)  The guys at Intel have
done this in the Linux driver.  I have implemented it in our
infrastructure code which means that we will enable it on any hardware
that reports capable.  The Intel guys have explicitly blacklisted a
couple of 945 class devices, stating that they report capable but don't
appear to work.  While I would like to get verification that these chips
don't work, don't be surprised if it doesn't work if you have chips 2772
or 27a2.  I have not implemented the blacklist bits yet.

The Linux crew has never enabled MSI on radeon hardware, though several
devices appear to report capable.  When I inquired as to why they hadn't
done so, they just stated that they hadn't gotten around to it.  I'm
particularly interested to see how this works on radeons.

In order to use this patch, you need to be running CURRENT as I had to
make a few other changes to vgapci to get this working. You can see if
you hardware is capable by running pciconf -lvc.  You will see something
like this:

vgapci0 at pci0:0:2:0:     class=0x030000 card=0x01f91028 chip=0x2a028086
rev=0x0c hdr=0x00
    vendor     = 'Intel Corporation'
    device     = 'Mobile 965 Express Integrated Graphics Controller'
    class      = display
    subclass   = VGA
    cap 05[90] = MSI supports 1 message 
    cap 01[d0] = powerspec 3  supports D0 D3  current D0

When drm loads it will also report that it has enabled MSI.

Please send me reports of what chips do/don't work.

The patch is located at:

http://people.freebsd.org/~rnoland/drm-msi.patch

robert.
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