-CURRENT barfing on UDMA on Via 8233

Okay, it looks like some UDMA stuff broke sometime between 5.2-R and current
as of two days ago.  I couldn't boot into the system unless in 'safe mode',
so I booted back into 5.2-R, re-sup'ed, rebuilt, and rebooted.  Same issue
as before:

    atapci0: <VIA 8233 UDMA100 controller> port 0xd400-0xd40f at device 17.1 on pci0
    ata0: at 0x1f0 irq 14 on atapci0
    ata0: [MPSAFE]
    ata1: at 0x170 irq 15 on atapci0
    ata1: [MPSAFE]
    ad0: 38166MB <ST340014A> [77545/16/63] at ata0-master UDMA100
    Mounting root from ufs:/dev/ad0s1a
    pid 86 (fsck_ufs), uid0: exited on signal 8
    pid 87 (fsck_ufs), uid0: exited on signal 8

Okay, fine and dandy.  Yes, a reboot with a dirty root resulted in the same
repeated error message about needing to fsck root before R/W mounting it, but
that's a separate problem.

So I took a closer look at the 'Safe Mode' booting, and here's what I see
instead:

    atapci0: <VIA 8233 UDMA100 controller> port 0xd400-0xd40f at device 17.1 on pci0
    ata0: at 0x1f0 irq 14 on atapci0
    ata0: [MPSAFE]
    ata1: at 0x170 irq 15 on atapci0
    ata1: [MPSAFE]
    ad0: 38166MB <ST340014A> [77545/16/63] at ata0-master PIO4
    Mounting root from ufs:/dev/ad0s1a

And then it continues to boot normally.  So I'm guessing that the UDMA (or
possibly just UDMA100) support for the 8233 controller is pooched?

FWIW, here's a snippet of a boot -v:

    ata0-master: pio=0x0c wdma=0x22 udma=0x45 cable=80pin
    ata0-master: setting PIO4 on VIA 8233 chip
    ata0-master: setting UDMA100 on VIA 8233 chip
    ad0: <ST340014A/3.06> ATA-6 disk at ata0-master
    ad0: 38166MB (78165360 sectors), 77545 C, 16 H, 63 S, 512 B
    ad0: 16secs/int, 1 depth queue, UDMA100
    GEOM: new disk ad0
    [0]: f:80 typ:165 s(CHS):0/1/1 e(CHS):1023/254/63 s:63 l:78156162
    [1]: f:00 typ:0 s(CHS):0/0/0 e(CHS):0/0/0 e:0 l:0
    [2]: f:00 typ:0 s(CHS):0/0/0 e(CHS):0/0/0 e:0 l:0
    [3]: f:00 typ:0 s(CHS):0/0/0 e(CHS):0/0/0 e:0 l:0
    GEOM: Configure ad0s1, start 32256 length 40015954944 end 40015987199
    GEOM: Configure ad0s1a, start 1073741824 length 1073741824 end 2147483647
    GEOM: Configure ad0s1b, start 0 length 1073741824 end 1073741823
    GEOM: Configure ad0s1c, start 0 length 40015954944 end 40015954943
    GEOM: Configure ad0s1d, start 2147483648 length 8589934592 end 10737418239
    GEOM: Configure ad0s1e, start 10737418240 length 29278536704 end 40015954943
    Mounting root from ufs:/dev/ad0s1a
    start_init: trying /sbin/init
    pid 86 (fsck_ufs), uid0: exited on signal 8
    pid 87 (fsck_ufs), uid0: exited on signal 8

And then we hang.  Again num/caps/scroll lock respond, so the whole machine
isn't frozen, but FBSD doesn't respond to anything.