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:

quoted

On Thu, Dec 31, 2015 at 04:50:54PM +0900, Masahiro Yamada wrote:

quoted

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.

-- 
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