From: per.forlin@linaro.org (Per Forlin)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH] dmaengine: Add API documentation for slave dma usage
Date: Wed, 25 May 2011 09:47:31 +0200 [thread overview]
Message-ID: <BANLkTikAm=D_YNFt0Regeas6AX8116L0-A@mail.gmail.com> (raw)
In-Reply-To: <BANLkTikjxECNAK5eS5hSu2bbEKpZX341Dw@mail.gmail.com>
On 24 May 2011 23:03, Dan Williams <dan.j.williams@intel.com> wrote:
> On Tue, May 24, 2011 at 9:06 AM, Koul, Vinod <vinod.koul@intel.com> wrote:
>> On Tue, 2011-05-24 at 17:40 +0200, Per Forlin wrote:
>>> Hi Vinod,
>>>
>>> On Tue, May 24, 2011 at 2:04 PM, Koul, Vinod <vinod.koul@intel.com> wrote:
>>> > From: Vinod Koul <vinod.koul@intel.com>
>>> >
>>> > Signed-off-by: Vinod Koul <vinod.koul@intel.com>
>>> > ---
>>> > ?Documentation/dma-slave-api.txt | ? 74 +++++++++++++++++++++++++++++++++++++++
>>> > ?1 files changed, 74 insertions(+), 0 deletions(-)
>>> > ?create mode 100644 Documentation/dma-slave-api.txt
>>> I suggest putting this in subsection of dmaengine.txt instead.
>>> dmaengine.txt would be the natural place to look at.
>> Agreed, that would make it easier for people to find
>>
>>> > +4. Submit the transaction(s) and wait for callback notification when slave API
>>> > +is 3 above returns, the non NULL value would imply a "descriptor" for the
>>> > +transaction. These transaction(s) would need to be submitted which pushes them
>>> > +into queue in DMA driver. If DMA is idle then the first descriptor submit will
>>> > +be pushed to DMA and subsequent ones will be queued. On completion of the DMA
>>> > +operation the next in queue is submitted and a tasklet triggered. The tasklet
>>> > +would then call the client driver completion callback routine for notification,
>>> > +if set.
>>> > +
>>> Does submit really start the transfer as well? My interpretation of
>>> submit is that is only adds desc to a pending queue. When calling
>>> issue_pending all these descs will be schedule for DMA transfer. Calls
>>> to submit after this point will added to the pending queue again and
>>> not be issued until calling issue_pending once more.
>> For slave dma devices, submit() is used to start the transaction if the
>> channel is idle. If its already doing a transaction then it will queue
>> it up and submit once cureent excuting one is completed. It is not
>> required to call issue_pending once more.
>> I am not sure if this is true for non slave usage, Dan would that be
>> correct for you as well?
>
> No, ->submit() is just an "add this descriptor to the chain"
> operation, and ->issue_pending() is always required to make sure the
> everything submitted previously is actively executing. ?This was a
> holdover from the very first dmaengine implementation where, for
> efficiency reasons, it could save mmio writes by batching the issuing
> of requests.
Thanks Dan for clarifying.
Vinod, I propose that the submit and issue_pending works the same for
SLAVE and none SLAVE channels. The API should have the same definition
independent of DMA_CAP. Please enlighten me if there are things I have
foreseen on this matter.
Thanks,
Per
next prev parent reply other threads:[~2011-05-25 7:47 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-05-24 12:04 [PATCH] dmaengine: Add API documentation for slave dma usage Koul, Vinod
2011-05-24 15:40 ` Per Forlin
2011-05-24 16:06 ` Koul, Vinod
2011-05-24 21:03 ` Dan Williams
2011-05-25 7:47 ` Per Forlin [this message]
2011-05-25 8:26 ` Koul, Vinod
2011-05-25 9:47 ` Per Forlin
2011-05-25 9:34 ` Koul, Vinod
2011-05-25 10:51 ` Per Forlin
2011-05-25 10:55 ` Koul, Vinod
2011-05-24 17:48 ` Russell King - ARM Linux
2011-05-25 8:34 ` Koul, Vinod
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='BANLkTikAm=D_YNFt0Regeas6AX8116L0-A@mail.gmail.com' \
--to=per.forlin@linaro.org \
--cc=linux-arm-kernel@lists.infradead.org \
/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).