linux-kernel - Re: [PATCH 08/11] MTD: m25p80: Add option to limit SPI transfer size.

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Date:	Wed, 15 Jul 2015 19:15:50 +0200
From:	Marek Vasut <marex@...x.de>
To:	Brian Norris <computersforpeace@...il.com>
Cc:	hramrach@...il.com, Richard Cochran <richardcochran@...il.com>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Mark Rutland <mark.rutland@....com>,
	Krzysztof Kozlowski <k.kozlowski@...sung.com>,
	Geert Uytterhoeven <geert+renesas@...der.be>,
	MTD Maling List <linux-mtd@...ts.infradead.org>,
	Alison Chaiken <alison_chaiken@...tor.com>,
	"Bean Huo 霍斌斌 (beanhuo)" 
	<beanhuo@...ron.com>,
	"linux-samsung-soc@...r.kernel.org" 
	<linux-samsung-soc@...r.kernel.org>,
	Russell King <linux@....linux.org.uk>,
	Vinod Koul <vinod.koul@...el.com>,
	Rafał Miłecki <zajec5@...il.com>,
	Kukjin Kim <kgene@...nel.org>,
	Ben Hutchings <ben@...adent.org.uk>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Pawel Moll <pawel.moll@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Mark Brown <broonie@...nel.org>,
	Dan Williams <dan.j.williams@...el.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"grmoore@...era.com" <grmoore@...era.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-spi" <linux-spi@...r.kernel.org>,
	Huang Shijie <b32955@...escale.com>,
	Rob Herring <robh+dt@...nel.org>,
	Han Xu <han.xu@...escale.com>,
	Knut Wohlrab <knut.wohlrab@...bosch.com>,
	dmaengine <dmaengine@...r.kernel.org>,
	David Woodhouse <dwmw2@...radead.org>
Subject: Re: [PATCH 08/11] MTD: m25p80: Add option to limit SPI transfer size.

On Wednesday, July 15, 2015 at 05:59:46 PM, Brian Norris wrote:
> Hi Michal,

Hi all,

> On Wed, Jul 15, 2015 at 01:52:27PM +0200, Marek Vasut wrote:
> > The problem is, if you add a new DT binding, you'd have to support it
> > forever, no matter how bad idea that binding turned out to be.
> 
> Agreed, and a solid NAK to this patch. I could have sworn I gave such a
> response when this was originally being discussed a month ago.
> 
> AFAICT, you have one of two general approaches available to you:
> 
> 1. Fix up the SPI driver so that it knows how to break large SPI
> transfers up into smaller segments that its constituent hardware (DMA
> controllers, fast clocks, etc.) can handle.

I think this might actually be easier -- just do a transfer where you
don't toggle CS and just stops the clock at the last bit, then do another
(multiple) transfers which don't toggle CS at all, then finally do a
transfer which toggles a CS at the end. This should be pretty trivial
to do and I think for example spi-mxs.c does this.

Best regards,
Marek Vasut
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