I saw this before sbus streaming cache was fixed by adding
BUS_DMA_COHERENT flags to bus_dmamap_load in hme.c.
I think iommu.c changes from BUS_DMA_COHERENT to BUS_DMA_STREAMING
broke the driver(s). The fix should be straightforward
replacing those defines in all sbus-related drivers to new define.
The patch for hme.c is below.

	Andrey

Index: hme.c
===================================================================
RCS file: /cvsroot/syssrc/sys/dev/ic/hme.c,v
retrieving revision 1.20
diff -c -r1.20 hme.c
*** hme.c       2000/12/14 06:27:25     1.20
--- hme.c       2001/03/21 00:27:56
***************
*** 232,238 ****
        /* Load the buffer */
        if ((error = bus_dmamap_load(dmatag, sc->sc_dmamap,
            sc->sc_rb.rb_membase, size, NULL,
!           BUS_DMA_NOWAIT|BUS_DMA_COHERENT)) != 0) {
                printf("%s: DMA buffer map load error %d\n",
                        sc->sc_dev.dv_xname, error);
                bus_dmamem_free(dmatag, &seg, rseg);
--- 232,238 ----
        /* Load the buffer */
        if ((error = bus_dmamap_load(dmatag, sc->sc_dmamap,
            sc->sc_rb.rb_membase, size, NULL,
!           BUS_DMA_NOWAIT|BUS_DMA_STREAMING)) != 0) {
                printf("%s: DMA buffer map load error %d\n",
                        sc->sc_dev.dv_xname, error);
                bus_dmamem_free(dmatag, &seg, rseg);