archive mirror
 help / color / mirror / Atom feed
* semantics of dma_map_single()
@ 2017-07-16  1:24 Vineet Gupta
  2017-07-17  6:42 ` Christoph Hellwig
  0 siblings, 1 reply; 4+ messages in thread
From: Vineet Gupta @ 2017-07-16  1:24 UTC (permalink / raw)
  To: linux-arch, linux-mm, Christoph Hellwig, bart.vanassche,
	Alexander Duyck, Krzysztof Kozlowski, Andrew Morton
  Cc: lkml, arcml

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.


To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to  For more info on Linux MM,
see: .
Don't email: <a href=mailto:""> </a>

^ permalink raw reply	[flat|nested] 4+ messages in thread

end of thread, other threads:[~2017-07-17 16:46 UTC | newest]

Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2017-07-16  1:24 semantics of dma_map_single() Vineet Gupta
2017-07-17  6:42 ` Christoph Hellwig
2017-07-17 16:06   ` Vineet Gupta
2017-07-17 16:46     ` James Bottomley

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).