linux-kernel - Re: [PATCH v4 00/14] DMA Engine support for AM33XX

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Message-ID: <20130111183349.GA14660@beef>
Date:	Fri, 11 Jan 2013 13:33:49 -0500
From:	Matt Porter <mporter@...com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Tony Lindgren <tony@...mide.com>, Sekhar Nori <nsekhar@...com>,
	Grant Likely <grant.likely@...retlab.ca>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Benoit Cousson <b-cousson@...com>,
	Russell King <linux@....linux.org.uk>,
	Vinod Koul <vinod.koul@...el.com>,
	Rob Landley <rob@...dley.net>, Chris Ball <cjb@...top.org>,
	Devicetree Discuss <devicetree-discuss@...ts.ozlabs.org>,
	Linux OMAP List <linux-omap@...r.kernel.org>,
	Linux ARM Kernel List <linux-arm-kernel@...ts.infradead.org>,
	Linux DaVinci Kernel List 
	<davinci-linux-open-source@...ux.davincidsp.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux Documentation List <linux-doc@...r.kernel.org>,
	Linux MMC List <linux-mmc@...r.kernel.org>,
	Linux SPI Devel List 
	<spi-devel-general@...ts.sourceforge.net>,
	Dan Williams <djbw@...com>,
	Rob Herring <rob.herring@...xeda.com>
Subject: Re: [PATCH v4 00/14] DMA Engine support for AM33XX

On Fri, Jan 11, 2013 at 11:40:41AM +0000, Arnd Bergmann wrote:
> On Friday 11 January 2013, Matt Porter wrote:
> > The approach taken is similar to how OMAP DMA is being converted to
> > DMA Engine support. With the functional EDMA private API already
> > existing in mach-davinci/dma.c, we first move that to an ARM common
> > area so it can be shared. Adding DT and runtime PM support to the
> > private EDMA API implementation allows it to run on AM33xx. AM33xx
> > only boots using DT so we leverage Jon's generic DT DMA helpers to
> > register EDMA DMAC with the of_dma framework and then add support
> > for calling the dma_request_slave_channel() API to both the mmc
> > and spi drivers.
> 
> I think this looks very good. What I wonder is whether we should
> make the non-DT parts of the dmaengine driver compile-time
> conditional on CONFIG_ATAGS though, so the slave drivers don't
> have a link-time dependency on the dmaengine driver's 
> omap_dma_filter_fn symbol when building without ATAGS support.

We have tightly coupled the link-time dependency for
omap_dma_filter_fn by going down the path of using
dma_request_slave_channel_compat() as Tony suggested to avoid extra
ifdefry.

That dependency will go away naturally if all the "legacy" OMAP platforms
were required to only boot from DT...just as a newly added SoCs are.

Are you suggesting unwinding the _compat() approach?

-Matt
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