linux-kernel - Re: [PATCH v6 03/10] ARM: edma: add AM33XX support to the private EDMA API

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Date:	Thu, 31 Jan 2013 20:58:39 +0000
From:	Arnd Bergmann <arnd@...db.de>
To:	Matt Porter <mporter@...com>
Cc:	Linux DaVinci Kernel List 
	<davinci-linux-open-source@...ux.davincidsp.com>,
	Linux OMAP List <linux-omap@...r.kernel.org>,
	Russell King <linux@....linux.org.uk>,
	Benoit Cousson <b-cousson@...com>,
	Linux Documentation List <linux-doc@...r.kernel.org>,
	Tony Lindgren <tony@...mide.com>,
	Linux MMC List <linux-mmc@...r.kernel.org>,
	Devicetree Discuss <devicetree-discuss@...ts.ozlabs.org>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Rob Herring <rob.herring@...xeda.com>,
	Grant Likely <grant.likely@...retlab.ca>,
	Vinod Koul <vinod.koul@...el.com>,
	Rob Landley <rob@...dley.net>, Dan Williams <djbw@...com>,
	Padma Venkat <padma.kvr@...il.com>,
	Linux SPI Devel List 
	<spi-devel-general@...ts.sourceforge.net>,
	Chris Ball <cjb@...top.org>,
	Linux ARM Kernel List <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v6 03/10] ARM: edma: add AM33XX support to the private EDMA API

On Thursday 31 January 2013, Matt Porter wrote:
> On Wed, Jan 30, 2013 at 09:32:58AM +0000, Arnd Bergmann wrote:
> > On Wednesday 30 January 2013, Matt Porter wrote:
> > > +               dma_cap_set(DMA_SLAVE, edma_filter_info.dma_cap);
> > > +               of_dma_controller_register(dev->of_node,
> > > +                                          of_dma_simple_xlate,
> > > +                                          &edma_filter_info);
> > > +       }
> > 
> > How do you actually deal with the problem mentioned by Padma, that
> > the filter function does not know which edma instance it is looking
> > at? If you assume that there can only be a single edma instance in
> > the system, that is probably a limitation that should be documented
> > somewhere, and ideally the probe() function should check for that.
> 
> I make an assumption of one edma instance in the system in the case of
> DT being populated. This is always true right now as the only SoC with
> two EDMA controllers in existence is Davinci DA850. Until recently,
> Davinci had no DT support. Given the steady work being done today on DT
> support for DA850, it'll probably be something needed in 3.10.
> 
> I will add a comment and check in probe() to capture this assumption
> and then plan to update separately to support DA850 booting from DT.

Ok, sounds good. Hopefully by then we will already have a nicer
way to write an xlate function that does not rely on a filter
function.

	Arnd
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