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

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Date:	Mon, 04 Feb 2013 21:22:42 +0300
From:	Sergei Shtylyov <sshtylyov@...sta.com>
To:	balbi@...com
CC:	Russell King - ARM Linux <linux@....linux.org.uk>,
	Matt Porter <mporter@...com>,
	Linux DaVinci Kernel List 
	<davinci-linux-open-source@...ux.davincidsp.com>,
	Chris Ball <cjb@...top.org>,
	"Cousson, Benoit" <b-cousson@...com>,
	Arnd Bergmann <arnd@...db.de>,
	Linux Documentation List <linux-doc@...r.kernel.org>,
	Tony Lindgren <tony@...mide.com>,
	Devicetree Discuss <devicetree-discuss@...ts.ozlabs.org>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Linux MMC List <linux-mmc@...r.kernel.org>,
	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>,
	Linux SPI Devel List 
	<spi-devel-general@...ts.sourceforge.net>,
	Linux OMAP List <linux-omap@...r.kernel.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 02/04/2013 08:02 PM, Felipe Balbi wrote:

>>> On Mon, Feb 04, 2013 at 08:36:38PM +0300, Sergei Shtylyov wrote:
>>>>> opted out of it. From the top of my head we have CPPI 3.x, CPPI 4.1,
>>>>> Inventra DMA, OMAP sDMA and ux500 DMA engines supported by the driver.

>>>>> Granted, CPPI 4.1 makes some assumptions about the fact that it's
>>>>> handling USB tranfers,

>>>>    What CPPI 4.1 code makes this assumptions? MUSB DMA driver? Then it's just

>>> HW makes the asumptions

>>    Not true at all. There is a separate set of registers (at offset 0) which
>> copes with USB specifics, but CPPI 4.1 itself doesn't know about USB anything.

> CPPI 4.1 was made for USB transfers.

   Utter nonsense, CPPI 4.1 is hardware abstract DMA engine. It's used for
Ethernet transfers on out-of-tree platforms like mach-avalanche/.

>> It's just the way the driver was written that it used both sets of registers but
>> this needs to be changed into more abstacted accesses to the USB-specific part,
>> to cope with it being different on different platfroms, like AM35x. The driver
>> as it was last posted, just needs rework now.

> are you saying you will do the work ?

   My efforts stopped to be funded by MV back in 2010. Hell, I'm not even
working in MV as I used to, hanging on the verge of my current contract being
terminated.

>>>>    Don't know, I was quite content with the abstraction when writing CPPI 4.1
>>>> driver for MUSB...

>>> look closer. The whole:

>>> if (is_cppi())
>>> 	foo();
>>> else if (is_inventra())
>>> 	bar();
>>> else if (is_omap_sdma())
>>> 	baz();

>>> is bogus.

>>    That part -- yes. There were attempt to get rid of this, but without changing
>> the DMA API. It was left halfway done after my only critical comment, IIRC. Will
>> we ever see the continuation of this effort?

> patches are welcome

   There was a patch, it only needed comments addressed. I think the author was
Heikki Krogerus. As for me, my time is very limited, so be thankful even for
those scarce patches I'm sending out now -- I'm doing them in my copious free time.

WBR, Sergei

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