linux-kernel - Re: [PATCH 1/3] dmaengine: add dma_get_slave_sg

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Date:	Mon, 22 Jul 2013 16:45:51 -0500
From:	Joel Fernandes <joelf@...com>
To:	Vinod Koul <vinod.koul@...el.com>
CC:	Tony Lindgren <tony@...mide.com>, Sekhar Nori <nsekhar@...com>,
	Matt Porter <matt@...orter.com>,
	Grant Likely <grant.likely@...retlab.ca>,
	Rob Herring <rob.herring@...xeda.com>,
	Mark Brown <broonie@...aro.org>,
	Benoit Cousson <benoit.cousson@...aro.org>,
	Russell King <linux@....linux.org.uk>,
	Balaji TK <balajitk@...com>,
	Gururaja Hebbar <gururaja.hebbar@...com>,
	Chris Ball <cjb@...top.org>,
	Jason Kridner <jkridner@...gleboard.org>,
	Mark Jackson <mpfj-list@...flow.co.uk>,
	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>,
	Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH 1/3] dmaengine: add dma_get_slave_sg_limits()

On 07/18/2013 11:16 AM, Vinod Koul wrote:> On Thu, Jul 18, 2013 at
11:46:39AM -0500, Joel Fernandes wrote:
>> From: Matt Porter <mporter@...com>
>>
>> Add a dmaengine API to retrieve slave SG transfer limits.
>>
>> The API is optionally implemented by dmaengine drivers and when
>> unimplemented will return a NULL pointer. A client driver using
>> this API provides the required dma channel, address width, and
>> burst size of the transfer. dma_get_slave_sg_limits() returns an
>> SG limits structure with the maximum number and size of SG segments
>> that the given channel can handle.
> Hi Joel,
>
> I have already resurrected this and generalized the API to get the slave
> capablities.
> https://lkml.org/lkml/2013/7/15/147

Hi Vinod,

get_caps and get_sg_limits are 2 different things, looks like this was
already discussed earlier, and this patch series is a separate API that
adds support for SG limits.

Infact, you can already see here that he changed the name of the
function from caps to dma_get_slave_sg_limits:
http://linux.davincidsp.com/pipermail/davinci-linux-open-source/2013-March/026601.html

Considering this, what is the way forward? Can this patch series be
merged as it is a different API as discussed above?

Summarizing:
* get_caps API cannot be used for this same purpose, as get_caps is done
_before_ the DMA channel can be configured from what it looks like:
* get_sg_limits, on the other hand is supposed to already have the
parameters required for configuring the DMA channel before hand.

Are there any other changes to the get_sg_limits series you would like
before it can be applied? Any other suggestions?

Thanks,

-Joel

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