[email protected] wrote:
> Reorderings are possible on reads and
> writes. Things get synced up by either an interrupt or a write to
> a memory region with a "barrier attribute". Memory allocated with
> dma_alloc_coherent() gets the barrier attribute. The idea here is
> to allow memory allocated with plain old malloc() or whatever to
> get the same attribute.
>From its purpose it sounds like you need this only for few special
memory regions which would typically be mapped by dma_map_single() and
furthermore that drivers who need this behavior will be changed to
explicitly demand it. If so, a nonintrusive API extension could simply
be to add an
dma_addr_t dma_map_single_write_last(struct device *dev, void *ptr,
size_t size, enum dma_data_direction direction);
or however you'd like to call it. (DMA-maps a memory area for which it
is guaranteed that of all DMA writes pending at any time, a DMA
reordering interconnect --- if such an interconnect is present --- will
perform DMAs to other areas first and to this area last. On machines
which don't reorder DMAs, this function is the same as dma_map_single().)
However, your older patch series looks like you want this behavior also
in areas which are mapped by dma_map_sg(), do you?. Still, adding two
functions of the kind like above, if necessary, might still be
preferable to changing the call parameters of existing functions or to
overloading enum dma_data_direction.
So that would be option 3) of yours, though without your attrs
parameter. Do you expect the need for even more flags for other kinds
of special behavior?
--
Stefan Richter
-=====-=-=== ==-- =--=-
http://arcgraph.de/sr/
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