linux-kernel - Re: [PATCH 5/9] ARM: dts: provide DMA config to pxamci

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Date:	Mon, 09 Dec 2013 16:09:18 +0400
From:	Sergei Ianovich <ynvich@...il.com>
To:	Daniel Mack <zonque@...il.com>
Cc:	Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	Rob Herring <rob.herring@...xeda.com>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Stephen Warren <swarren@...dotorg.org>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Rob Landley <rob@...dley.net>,
	Russell King <linux@....linux.org.uk>,
	Chris Ball <cjb@...top.org>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	Jaehoon Chung <jh80.chung@...sung.com>,
	Seungwon Jeon <tgih.jun@...sung.com>,
	"open list:OPEN FIRMWARE AND..." <devicetree@...r.kernel.org>,
	DOCUMENTATION <linux-doc@...r.kernel.org>,
	Robert Jarzmik <robert.jarzmik@...e.fr>
Subject: Re: [PATCH 5/9] ARM: dts: provide DMA config to pxamci

On Mon, 2013-12-09 at 11:21 +0100, Daniel Mack wrote:
> On 12/09/2013 10:34 AM, Sergei Ianovich wrote:
> > Nice to have Daniel in this conversation. Your patch series is a big and
> > important work. However, I am not sure I will ever land as is exactly
> > for this reason.
> 
> Well, I wouldn't be so certain about that statement. As I wrote in the
> cover letter, most of the work is actually done, and I successfully
> tested the new DMA support with a some of the drivers I ported. Others
> were ported blindly, and in case of no reaction, I'd dare to merge them
> and wait for people to report back in case of trouble.

If breaking things is an option, I am definitely wrong. I assumed the
opposite.

> > My proposal in to actually add new drivers for each platform device with
> > DMA and mark new ones EXPERIMENTAL.
> 
> That would cause tree-wide cross-dependencies between drivers, because
> the two DMA controllers can't be used at the same time, and the PXA
> specific API will be unavailable when the mmp-dma driver is selected. My
> patch series (and the DMA controller framework for that matter) aims for
> the opposite - the unification of APIs and drivers.

Not sure I got this point. My proposal is to keep the existing DMA
intact until we are ready to remove it. I understand this approach
requires considerably more work inside DMA to allow both driver to
coexist than wholesale replacement. I still think big change is risky.

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