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

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Message-ID: <20140819144423.GE30401@n2100.arm.linux.org.uk>
Date:	Tue, 19 Aug 2014 15:44:23 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Vinod Koul <vinod.koul@...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 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.

Ignoring it until it can be understood and documented is an approach I
would agree with though.

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