linux-kernel - Re: [PATCH v7 01/10] ARM: davinci: move private EDMA API to arm/common

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Date:	Sat, 2 Feb 2013 13:07:47 -0500
From:	Matt Porter <mporter@...com>
To:	Sergei Shtylyov <sshtylyov@...sta.com>
Cc:	Tony Lindgren <tony@...mide.com>,
	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>,
	"Cousson, Benoit" <b-cousson@...com>,
	Arnd Bergmann <arnd@...db.de>,
	Linux Documentation List <linux-doc@...r.kernel.org>,
	Vinod Koul <vinod.koul@...el.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>,
	Rob Landley <rob@...dley.net>, Dan Williams <djbw@...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 v7 01/10] ARM: davinci: move private EDMA API to
 arm/common

On Sat, Feb 02, 2013 at 12:01:37AM +0000, Sergei Shtylyov wrote:
> Hello.
> 
> On 01-02-2013 22:59, Matt Porter wrote:
> 
> >>>>> Move mach-davinci/dma.c to common/edma.c so it can be used
> >>>>> by OMAP (specifically AM33xx) as well.
> 
> >>>> I think this should rather go to drivers/dma/?
> 
> >>> No, this is the private EDMA API. It's the analogous thing to
> >>> the private OMAP dma API that is in plat-omap/dma.c. The actual
> >>> dmaengine driver is in drivers/dma/edma.c as a wrapper around
> >>> this...same way OMAP DMA engine conversion is being done.
> 
> >>    Keeps me wondering why we couldn't have the same with CPPI 4.1 when I proposed
> >> that, instead of waiting indefinitely for TI to convert it to drivers/dma/
> >> directly. We could have working MUSB DMA on OMAP-L1x/Sitara all this time... Sigh.
> 
> > That is a shame. Yeah, I've pointed out that I was doing this exactly
> > the same way as was acceptable for the OMAP DMA conversion since it was
> > in RFC. The reasons are sound since in both cases, we have many drivers
> > to convert that need to continue using the private DMA APIs.
> 
>     In case of CPPI 4.1, we'd only have to convert MUSB DMA driver. Other 
> in-tree CPPI 4.1 having SoCs don't use it for anything but MUSB -- it even is 
> sub-block of their MUSB device, AFAIK (I maybe wrong about Sitaras -- I don't 
> know them well).

Well, it's pretty clear to me now that there's good reason for it not
landing in arch/arm/ so the obvious path is to do the dmaengine
conversion and put it in drivers/dma/ if it's really a generic dma engine.
I'm not sure why you express concern over the dma engine api not fitting
with CPPI 4.1? If it doesn't work, work with Vinod to fix the api. It's
expected, I'm working on dmaengine API changes right now to deal with a
limitation of EDMA that needs to be abstracted.

As pointed out, edma.c is already here in arch/arm/, so moving it doesn't
add something new. It does let us regression test all platforms that use it
(both Davinci and AM33xx) as I go through the conversion process.

-Matt
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