RFC bus_dma_tag_parent

[Joerg Sonnenberger]

On Wed, Nov 10, 2004 at 02:20:08PM -0800, Chuck Tuffli wrote:
>   bus_dma_tag_parent(dev)
> 
>   Returns the DMA tag of the bus dev connects to. Drivers can use the
>   DMA tag for the parent parameter in subsequent calls to
>   bus_dma_tag_create(9). All devices on a bus share this tag as their
>   parent and should not destroy it.
> 
>   Returns NULL if tag does not exist or a bus_dma_tag_t on success.

I still think having an option to specify the number of maximum number of
segments would be useful. This is not a problem here, because e.g. for
PCI it can be ignored or used as INVARIANT.

I also think we want to have the address constraints in the parent tag.

Joerg