Re: RFC bus_dma_tag_parent
:while the proposal would look like
:
: parent_dmat = bus_dma_tag_parent(dev);
: bus_dma_tag_create(parent_dmat, ..., &mybuffer_dmat);
:
:What kind of situations would specifying the max number of segments be
:useful?
:
:--
:Chuck Tuffli
:Agilent Technologies
For PCI the PCI BUS itself doesn't control DMA, so the pci bus would
specify '0' there (we'd make '0' officially mean 'unlimited or
unspecified'). Other busses would depend, but for the most part the
only thing that truely matters for their tags are the address
limitations of the bus.
The device driver would also specify limitations based on knowledge of
the device chip. e.g. if a PCI chipset's dma chaining structure only
has room for e.g. 32 bit addresses, then the device driver would also
specify a 32 bit limitation for its tag.
-Matt
Matthew Dillon
<dillon@backplane.com>
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