Re: RFC bus_dma_tag_parent
On Sat, Nov 13, 2004 at 01:13:05PM -0800, Matthew Dillon wrote:
....
> Perhaps this is just a naming convention problem. My take was that
> the purpose of bus_dma_tag_parent() was simply to retrieve the parent's
> dma tag so it could be used as the first argument in a call to
> bus_dma_tag_create().
>
> e.g.
>
> device {
> bus_dma_tag_t = bus_dma_tag_create(bus_dma_tag_parent(dev), align,
> boundary, lowaddr, highaddr, etc...);
> }
yup, this is problem i was trying to fix
>
> Now, there are certainly some restrictions to the current
> bus_dma_tag_create() function. It does not give the parent(s) any
> ability to modify the parameters to the device's new dma tag other
> then through inheritance.
>
> If we want to give the parent(s) more control over how the child's tag
> is created we would want to change bus_dma_tag_create() from a fixed
> function in i386 to a DEVMETHOD. I still believe we would also need
> to have a bus_dma_tag_parent() DEVMETHOD, but the separation of
> functionality seems fairly clear to me.
>
[description of parent/create split]
>
> Well, does that make any sense ?
>
> -Matt
this makes sense to me. if there aren't other objections, i'll start
the documentation and implementation.
--
Chuck Tuffli
Agilent Technologies
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