linux-kernel - Re: [PATCH] Documentation: dmaengine: Add a documentation for the dma controller API

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Message-ID: <20140819145734.GN13288@intel.com>
Date:	Tue, 19 Aug 2014 20:27:34 +0530
From:	Vinod Koul <vinod.koul@...el.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>,
	Dan Williams <dan.j.williams@...el.com>
Cc:	Ludovic Desroches <ludovic.desroches@...el.com>,
	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	Dan Williams <dan.j.williams@...el.com>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	dmaengine@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
	Antoine Ténart <antoine@...e-electrons.com>,
	Thomas Petazzoni <thomas@...e-electrons.com>,
	Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
	Boris Brezillon <boris@...e-electrons.com>,
	Matt Porter <matt.porter@...aro.org>,
	laurent.pinchart@...asonboard.com,
	Gregory Clement <gregory.clement@...e-electrons.com>,
	Nicolas Ferre <nicolas.ferre@...el.com>
Subject: Re: [PATCH] Documentation: dmaengine: Add a documentation for the
 dma controller API

On Tue, Aug 19, 2014 at 03:44:23PM +0100, Russell King - ARM Linux wrote:
> On Tue, Aug 19, 2014 at 07:15:07PM +0530, Vinod Koul wrote:
> > On Thu, Aug 14, 2014 at 09:57:53AM +0100, Russell King - ARM Linux wrote:
> > > 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.
> 
> We shouldn't ignore it - ignoring it makes it harder to implement a DMA
> engine driver which supports both the slave and async APIs, because
> we then need to know the reason for the channel being requested.
Do you have such usage coming up near future :)
> 
> Ignoring it until it can be understood and documented is an approach I
> would agree with though.
Certainly, I am asking Dan to add more clarity on these bits to help
improve.

-- 
~Vinod
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