From: vinod.koul@intel•com (Vinod Koul)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH] Documentation: dmaengine: Add a documentation for the dma controller API
Date: Tue, 19 Aug 2014 19:15:07 +0530 [thread overview]
Message-ID: <20140819134507.GJ13288@intel.com> (raw)
In-Reply-To: <20140814085753.GS30401@n2100.arm.linux.org.uk>
On Thu, Aug 14, 2014 at 09:57:53AM +0100, Russell King - ARM Linux wrote:
> On Thu, Aug 14, 2014 at 10:53:01AM +0200, Ludovic Desroches wrote:
> > On Wed, Jul 30, 2014 at 06:03:13PM +0200, Maxime Ripard wrote:
> > > The dmaengine is neither trivial nor properly documented at the moment, which
> > > means a lot of trial and error development, which is not that good for such a
> > > central piece of the system.
> > >
> > > Attempt at making such a documentation.
> >
> > Good idea, many questions are asked when writing a new dmaengine driver.
> >
> > For instance I didn't find how to use the DMA_CTRL_ACK flags.
> >
> > - How this flag has to be managed? For instance, async_tx_ack is used in
> > dmaengine driver but also in some devices.
> > - Is it mandatory to deal with this flag? It seems some dmaengine
> > drivers don't care about it.
> This is one part of the DMA engine API that even I don't understand.
>
> It's got something to do with the async engine API, and seems to be
> something to do with whether a descriptor can have other transactions
> added to it, and whether a descriptor can be re-used (async-tx engines
> typically allocate a fixed set of descriptors and recycle them.)
Yes this is my understanding too. Async API IIUC can reuse descriptors and
if engine doesnt support this is a way to tell them please do use that.
For slave dmanegine API we need to ignore it.
>
> I was never able to get to the bottom of what that flag meant or how
> it should be used with the DMA slave API (and I suspect everyone else
> just gave up trying to understand it as well.)
--
~Vinod
next prev parent reply other threads:[~2014-08-19 13:45 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-07-30 16:03 [PATCH] Documentation: dmaengine: Add a documentation for the dma controller API Maxime Ripard
2014-07-30 16:06 ` Vinod Koul
2014-07-31 7:44 ` Maxime Ripard
2014-07-31 11:56 ` Vinod Koul
2014-07-31 16:23 ` Maxime Ripard
2014-08-01 17:13 ` Vinod Koul
2014-08-02 14:49 ` Maxime Ripard
2014-08-02 15:17 ` Russell King - ARM Linux
2014-08-02 19:06 ` Maxime Ripard
2014-08-05 16:25 ` Vinod Koul
2014-07-31 12:44 ` Lars-Peter Clausen
2014-07-31 16:13 ` Maxime Ripard
2014-07-31 16:54 ` Lars-Peter Clausen
2014-07-31 17:37 ` Maxime Ripard
2014-08-01 8:00 ` Lars-Peter Clausen
2014-08-01 8:57 ` Maxime Ripard
2014-08-01 17:15 ` Vinod Koul
2014-08-01 18:09 ` Lars-Peter Clausen
2014-08-02 15:13 ` Maxime Ripard
2014-08-04 7:16 ` Lars-Peter Clausen
2014-07-31 13:22 ` Russell King - ARM Linux
2014-07-31 16:41 ` Maxime Ripard
2014-08-01 14:53 ` Russell King - ARM Linux
2014-08-02 15:11 ` Maxime Ripard
2014-08-02 15:29 ` Russell King - ARM Linux
2014-08-02 19:05 ` Maxime Ripard
2014-08-01 17:22 ` Vinod Koul
2014-08-05 8:16 ` Geert Uytterhoeven
2014-08-14 8:53 ` Ludovic Desroches
2014-08-14 8:57 ` Russell King - ARM Linux
2014-08-19 13:45 ` Vinod Koul [this message]
2014-08-19 14:44 ` Russell King - ARM Linux
2014-08-19 14:57 ` Vinod Koul
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