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Clarify that you shouldn't use the bus_dma_segment_t return value from

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bus_dmamem_alloc to program DMA registers, but that the dm_segs array
of a successfully loaded DMA mapping should be used.
This commit is contained in:
fvdl 2000-05-01 23:12:20 +00:00
parent e3358cb8ef
commit 015216d717
1 changed files with 13 additions and 3 deletions
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16
share/man/man9/bus_dma.9
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@ -1,4 +1,4 @@
.\" $NetBSD: bus_dma.9,v 1.12 2000/04/19 07:57:50 soren Exp $
.\" $NetBSD: bus_dma.9,v 1.13 2000/05/01 23:12:20 fvdl Exp $
.\"
.\" Copyright (c) 1996, 1997, 1998 The NetBSD Foundation, Inc.
.\" All rights reserved.
@ -452,10 +452,20 @@ always succeeds.
.\" XXX: This does not work with all the arguments.
.It Fn bus_dmamem_alloc "tag" "size" "alignment" "boundary" "segs" "..."
Allocates memory that is "DMA safe" for the bus corresponding to the
given tag. The mapping of this memory is machine-dependent (or
given tag.
.Pp
The mapping of this memory is machine-dependent (or
"opaque"); machine-independent code is not to assume that the
addresses returned are valid in kernel virtual address space, or that
the addresses returned are system physical addresses.
the addresses returned are system physical addresses. The address value
returned as part of
.Fa segs
can thus not be used to program DMA controller address registers. Only
the values in the
.Fa dm_segs
array of a sucessfully loaded DMA map (using
.Fn bus_dmamap_load
) can be used for this purpose.
.Pp
Allocations will always be rounded to the hardware page size. Callers
may wish to take advantage of this, and cluster allocation of small