About PHYS_TO_DMAP

Hi,

I'm struggling to understand which KVA will be returned by PHYS_TO_DMAP
on arm64. For example, if I'll create a DMA tag this way:

	bus_dma_tag_create(
	    bus_get_dma_tag(dev),
	    sc->buf_align, 0,		/* alignment, boundary */
	    DMAP_MAX_PHYSADDR,		/* low restricted addr */
	    DMAP_MIN_PHYSADDR,		/* high restricted addr */
	    NULL, NULL,			/* filter, filterarg */
	    BUF_SIZE, 1,		/* maxsize, nsegments */
	    BUF_SIZE, 0,		/* maxsegsize, flags */
	    NULL, NULL,			/* lockfunc, lockarg */
	    &dmat);

in order to restrict any physical addresses but a window defined by
DMAP_MIN_PHYSADDR and DMAP_MAX_PHYSADDR. Later on when I'll be
mapping my mbuf (BUF_SIZE) with

	bus_dmamap_load_mbuf_sg(dmat, dmap,
	    m, &segs, &nsegs, BUS_DMA_NOWAIT);

I expect that

	m->m_data == PHYS_TO_DMAP(segs[0].ds_addr)

but it isn't true. Could somebody explain what exactly is returned by
PHYS_TO_DMAP in this case and whether it's possible to translate
physical address to KVA as fast as possible (O(1) ideally).

Regards,
Dmitry

--
Open source software/hardware enthusiast
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