As far as the kernel mode setting, I haven't gotten that working on an SGI. Actually, the only really working support (as in testable with a released distro) right now is Intel's integrated graphics. If Intel actually releases Larabee, that should work too. Open source radeon support is going to be included in kernel 2.6.27 or .28 (I know the devs. that are working on the ATI side - and have told them about my plans to put a card in an O2) but the current stable linux release is 2.6.25 so we're a few months off. When I get it working, I'll let everyone here know.
You're a little overconfident, to say the least. There are no definitive plans for Radeon kernel modesetting. It'll happen, yes. But currently, there is no timeline. Jerome Glisse is the person to talk to about kernel modesetting for radeon. I suggest you talk with him, as what you say about .27 and .28 is simply not the case as far as I can see. His modesetting code is available in his personal git repository (
http://gitweb.freedesktop.org/?p=users/ ... ;a=summary
) but it hasn't been touched since December 2007.
Also, kernel modesetting is useless if the card cannot be initialized (POST'd) first. It's not as easy as finding a PCI Radeon and throwing it in a MIPS box, or an HPPA box, or SPARC, or PPC. They all have different ROMs with the code for the appropriate architecture's initialization. This is why ATI produces FireGL cards for HP's PA-RISC workstations and Radeons for PPC Macs. They contain code specific to the platform for which they're intended. The HP C8000 can be equipped with FireGL cards. Unfortunately though, there is still no DRI support for them under Linux/HPPA. I'm not sure X11 works on the C8000 under Linux in any case, actually.
Now, assuming you could get an X1550 (or even a Radeon 9100) with the appropriate MIPS initialization ROM, which, mind you, wouldn't be possible since there were never any Radeons made for MIPS boxes, Linux isn't guaranteed to work. For instance, I've got an Alphaserver DS20L. The good engineers at Digital were kind enough to implement an x86 BIOS emulator into SRM so that x86 add-on cards could easily work in Alpha systems even without the appropriate ROMs. The card works with xf86-video-radeonhd and crashes with xf86-video-ati. It's quite possible that whatever causes xf86-video-ati to crash has been fixed in more recent versions. Unfortunately, more recent versions of X11 require libpciaccess which in turn requires the kernel to allow access to PCI resources through sysfs. This feature has never been needed on Alpha, and is therefore not implemented. (
Kernel Bug Report
All in all, it's not as easy to get a graphics card to work with strange hardware as it is to plug on into the strange hardware. I'm also not sure you've got any of your facts straight.
The only way I can see to use an x86 graphics card in a MIPS box is to find one that doesn't have an initialization routine. Matrox and Voodoo 3s come to mind.