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Cc: John-Mark Gurney <gurney_j@resnet.uoregon.edu>, freebsd-current@freebsd.org,
	Poul-Henning Kamp <phk@phk.freebsd.dk>, freebsd-drivers@freebsd.org
Subject: Re: bus_get_dma_tag now necessary for drivers using bus_dma
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On Tuesday 05 September 2006 20:31, Scott Long wrote:
> Poul-Henning Kamp wrote:
> > In message <20060905173334.GH9421@funkthat.com>, John-Mark Gurney writes:
> >>This means that for each call to bus_dma_tag_create, instead of passing
> >>a NULL pointer, you should call bus_get_dma_tag(yourdev) and use that
> >>as the parent tag.  I committed some example code to various drivers,
> >>such as ahc, ata, em, and ohci.
> >
> > If there are never any exeptions to this requirement, why not
> > pass "yourdev" and have the magic hidden, rather than add 17
> > ritual characters to the API ?
>
> Drivers can have their own multi-level tag heirarchy.  You'd have to
> create a new bus_dma_tag_create() variant that expected a device_t
> instead of a bus_dma_tag_t.  This might be a good idea.
>

I think it is easier to share code with NetBSD if we use 
"bus_get_dma_tag(yourdev)".

For example I use the following prototype on NetBSD and FreeBSD:

void *
usbd_mem_alloc(bus_dma_tag_t parent, u_int32_t size,
               u_int8_t align_power);

--HPS