Date: Wed, 22 Jul 2015 10:19:25 +0530
From: Vinod Koul <vinod.koul@intel.com>
To: Michal Suchanek <hramrach@gmail.com>
Cc: Brian Norris <computersforpeace@gmail.com>, Marek Vasut <marex@denx.de>,
        Richard Cochran <richardcochran@gmail.com>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Krzysztof Kozlowski <k.kozlowski@samsung.com>,
        Geert Uytterhoeven <geert+renesas@glider.be>,
        MTD Maling List <linux-mtd@lists.infradead.org>,
        Alison Chaiken <alison_chaiken@mentor.com>,
        Bean Huo =?utf-8?B?6ZyN5paM5paMIChiZWFuaHVvKQ==?= 
	<beanhuo@micron.com>,
        "linux-samsung-soc@vger.kernel.org" 
	<linux-samsung-soc@vger.kernel.org>,
        Russell King <linux@arm.linux.org.uk>,
        =?utf-8?B?UmFmYcWCIE1pxYJlY2tp?= <zajec5@gmail.com>,
        Kukjin Kim <kgene@kernel.org>, Ben Hutchings <ben@decadent.org.uk>,
        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        Pawel Moll <pawel.moll@arm.com>,
        Ian Campbell <ijc+devicetree@hellion.org.uk>,
        Kumar Gala <galak@codeaurora.org>, Mark Brown <broonie@kernel.org>,
        Dan Williams <dan.j.williams@intel.com>,
        "linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>,
        "grmoore@altera.com" <grmoore@altera.com>,
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        linux-spi <linux-spi@vger.kernel.org>,
        Huang Shijie <b32955@freescale.com>, Rob Herring <robh+dt@kernel.org>,
        Han Xu <han.xu@freescale.com>,
        Knut Wohlrab <knut.wohlrab@de.bosch.com>,
        dmaengine <dmaengine@vger.kernel.org>,
        David Woodhouse <dwmw2@infradead.org>
Subject: Re: [PATCH 08/11] MTD: m25p80: Add option to limit SPI transfer size.
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On Tue, Jul 21, 2015 at 10:14:11AM +0200, Michal Suchanek wrote:
> > Or alternatively we could publish the limitations of the channel using
> > capabilities so SPI knows I have a dmaengine channel and it can transfer max N
> > length transfers so would be able to break rather than guessing it or coding
> > in DT. Yes it may come from DT but that should be dmaengine driver rather
> > than client driver :)
> >
> > This can be done by dma_get_slave_caps(chan, &caps)
> >
> > And we add max_length as one more parameter to existing set
> >
> > Also all this could be handled in generic SPI-dmaengine layer so that
> > individual drivers don't have to code it in
> >
> > Let me know if this idea is okay, I can push the dmaengine bits...
> 
> It would be ok if there was a fixed limit. However, the limit depends
> on SPI slave settings. Presumably for other buses using the dmaengine
> the limit would depend on the bus or slave settings as well. I do not
> see a sane way of passing this all the way to the dmaengine driver.
I don't see why this should be client (SPI) dependent. The max length
supported is a dmaengine constraint, typically flowing from max
blocks/length it can transfer. Know this limit can allow clients to split
transfers.

-- 
~Vinod
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