P.S. Apologies in advance for the explicit TO list, it seemed adding people who've
touched the dma mapping code (for ARC atleast), would respond sooner ;-)
The question is does dma_map_single() imply a single region (possibly > PAGE_SIZE)
or does it imply PAGE_SIZE. Documentation/DMA-API* is not explicit about one or
the other and the code below seems to point to "a" struct page, although it could
also mean multiple pages, specially if the pages are contiguous, say as those
returned by alloc_pages(with order > 0)
static inline dma_addr_t dma_map_single_attrs(dev, size, dir, attrs)
{
addr = ops->map_page(dev,
virt_to_page(ptr), <--- this is one struct page
offset_in_page(ptr), size, dir, attrs);
}
ARC dma_map_single() currently only handles cache coherency for only one struct
page or PAGE_SIZE worth of memory, and we have a customer who seem to assume that
it handles a region.
Looking at other arches dma mapping backend, it is not clear either what the
semantics are.
Thx,
-Vineet
