From: James Bottomley <James.Bottomley@HansenPartnership.com>
To: Russell King - ARM Linux <linux@arm.linux.org.uk>,
Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
dmaengine@vger.kernel.org, Lars-Peter Clausen <lars@metafoo.de>,
Vinod Koul <vinod.koul@intel.com>,
Nicolas Ferre <nicolas.ferre@atmel.com>,
Christoph Hellwig <hch@lst.de>,
Dan Williams <dan.j.williams@intel.com>,
Sumit Semwal <sumit.semwal@linaro.org>,
linux-arm-kernel <linux-arm-kernel@lists.infradead.org>
Subject: Re: [Question about DMA] Consistent memory?
Date: Sat, 02 Jan 2016 08:17:51 -0800 [thread overview]
Message-ID: <1451751471.2323.3.camel@HansenPartnership.com> (raw)
In-Reply-To: <20160102103948.GR8644@n2100.arm.linux.org.uk>
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.
James
next prev parent reply other threads:[~2016-01-02 16:17 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-12-31 7:50 [Question about DMA] Consistent memory? Masahiro Yamada
2015-12-31 8:38 ` Mike Looijmans
2015-12-31 10:25 ` One Thousand Gnomes
2015-12-31 14:57 ` Masahiro Yamada
2015-12-31 17:12 ` Mike Looijmans
2016-01-02 10:53 ` Russell King - ARM Linux
2016-01-02 10:39 ` Russell King - ARM Linux
2016-01-02 16:17 ` James Bottomley [this message]
2016-01-02 18:07 ` Russell King - ARM Linux
2016-01-02 18:35 ` Mike Looijmans
2016-01-02 20:10 ` James Bottomley
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=1451751471.2323.3.camel@HansenPartnership.com \
--to=james.bottomley@hansenpartnership.com \
--cc=dan.j.williams@intel.com \
--cc=dmaengine@vger.kernel.org \
--cc=hch@lst.de \
--cc=lars@metafoo.de \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux@arm.linux.org.uk \
--cc=nicolas.ferre@atmel.com \
--cc=sumit.semwal@linaro.org \
--cc=vinod.koul@intel.com \
--cc=yamada.masahiro@socionext.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
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).