Messages in this thread | | | Date | Tue, 18 Dec 2007 21:59:24 +0100 | From | Stefan Richter <> | Subject | Re: [RFC] dma: passing "attributes" to dma_map_* routines |
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akepner@sgi.com 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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