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

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Date:	Sat, 02 Feb 2013 23:06:06 +0400
From:	Sergei Shtylyov <sshtylyov@...sta.com>
To:	Matt Porter <mporter@...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

Hello.

On 02-02-2013 22:07, 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?

    It's not a DMA controller only, it's 3 distinct devices, with the DMA 
controller being one among them and using another one, the queue manager, as 
some sort of proxy. The third device doesn't exist on OMAP-L1x SoCs -- it's 
the buffer manager.

> 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.

    Sorry, now it's TI's task. I no longer have time to work on this (my 
internal project to push OMAP-L1x support upstream has expired at Sep 2010) 
and my future in MV is very uncertain at this moment. Most probably I'll leave 
it (or be forced to leave).

> 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.

    Could have been the same with CPPI 4.1 in theory if it was added to 
mach-davinci/ back in 2009... we'd then only have to move it. EDMA code is 
much older of course, so it's probably more justified.

> -Matt

WBR, Sergei

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