On Sat, Jan 02, 2016 at 08:17:51AM -0800, James Bottomley wrote: > On Sat, 2016-01-02 at 10:39 +0000, Russell King - ARM Linux wrote: > > On Thu, Dec 31, 2015 at 04:50:54PM +0900, Masahiro Yamada wrote: > > > Hi. > > > > > > I am new to the Linux DMA APIs. > > > > > > First, I started by reading Documentation/DMA-API.txt, > > > but I am confused with the term "consistent memory". > > > > Just read "coherent memory" instead - the documentation confusingly > > uses the two terms to refer to the same thing. I think there was a > > patch a while back to replace "consistent" with "coherent" in this > > document, though I'm not sure what happened to it. > > It's an standards issue. The Document was originally based on the PCI > DMA API. All the PCI standards documentation refers to "consistent > memory" instead of "coherent memory". The original DMA API was > designed for PA-RISC and its standards documentation refers to > "coherent memory" hence the confusion. The two terms are equivalent, > but there's no real way of removing either without someone reading the > actual specs and wondering what the other term means. May it be an idea to add a footnote explaining that the two terms are interchangable and equivalent then - this is not the first time that people have asked questions about it, and I suspect that unless something is done, there will be a continuing stream of questions. -- RMK's Patch system: http://www.arm.linux.org.uk/developer/patches/ FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up according to speedtest.net. -- To unsubscribe from this list: send the line "unsubscribe dmaengine" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
