After updating to -current (aka 4.99.41) from 4.99.34, I've found that
radeontool no longer works. Some of the more questionable code in
radeontool that does mmapping of /dev/kmem fails, but even when that's
patched TDTRT, it still doesn't work.

FWIW, on my other 4.99.34 i386 box, I get this output:

pts/5 dogcow@burai: /usr/pkgsrc/net/libtorrent 2626 % sudo radeontool --debug dac on
01:00.0 VGA compatible controller: ATI Technologies Inc: Unknown device 4e50 (prog-if 00 [VGA])
        Subsystem: Hewlett-Packard Company: Unknown device 0890
        Flags: bus master, 66Mhz, medium devsel, latency 64, IRQ 10
        Memory at 98000000 (32-bit, prefetchable)
        I/O ports at 2000
        Memory at 90300000 (32-bit, non-prefetchable)
Radeon found. Base control address is 90300000.
reading RADEON_DAC_CNTL (58) is ff002102
writing RADEON_DAC_CNTL (58) -> ff002102

whereas on the -current one I get
pts/6 dogcow@shiny: /usr/obj/pkgsrc/sysutils/radeontool/work.i386/radeontool-1.5 2553 % sudo ./radeontool --debug dac on 
01:00.0 VGA compatible controller: ATI Technologies Inc: Unknown device 5460 (prog-if 00 [VGA])
        Subsystem: Dell Computer Corporation: Unknown device 2003
        Flags: bus master, fast devsel, latency 0, IRQ 11
        Memory at d0000000 (32-bit, prefetchable)
        I/O ports at de00
        Memory at dfdf0000 (32-bit, non-prefetchable)
Radeon found. Base control address is dfdf0000.
reading RADEON_DAC_CNTL (58) is ff00a102
writing RADEON_DAC_CNTL (58) -> ff002102

which both look kosher to me.

Any of you have clues as to what's happening?