The radeon man page says:
Option "AGPMode" "integer"
Set AGP data transfer rate. (used only when DRI is enabled)
1 -- x1 (default)
2 -- x2
4 -- x4
8 -- x8
others -- invalid
Setting the rate to "4" works as expected but when I set it to "8" in my xorg.conf for my radeon 9250, I get these messages in the log
agpgart: Found an AGP 3.0 compliant device at 0000:00:00.0
agpgart: X tried to set rate=x12. Setting to AGP3 x8 mode.
agpgart: Putting AGP V3 device at 0000:00:00.0 into 8x mode
agpgart: Putting AGP V3 device at 0000:02:00.0 into 8x mode
[drm] Loading R200 Microcode
This isn't a new bug - it's not something that's suddenly appeared in xorg-7.x or kernel 2.6.x - I've just not gotten around to reporting it in the last year or so since it doesn't seem to be harmful and I don't really know which component is at fault.
I saw this too, with the r300 driver, but I just ignored it.
Please file this bug at https://bugs.freedesktop.org and post the link here. Thanks!