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

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Date:	Wed, 22 Jul 2015 09:58:00 +0200
From:	Marek Vasut <marex@...x.de>
To:	Michal Suchanek <hramrach@...il.com>
Cc:	Vinod Koul <vinod.koul@...el.com>,
	Brian Norris <computersforpeace@...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>,
	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 22, 2015 at 09:45:27 AM, Michal Suchanek wrote:
> On 22 July 2015 at 09:33, Marek Vasut <marex@...x.de> wrote:
> > On Wednesday, July 22, 2015 at 09:30:54 AM, Michal Suchanek wrote:
> >> On 22 July 2015 at 06:49, Vinod Koul <vinod.koul@...el.com> wrote:
> >> > 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.
> >> 
> >> In practice on the board I have the maximum transfer length before it
> >> fails depends on SPI bus speed which is set up per slave. I did not
> >> try searching the space of possible settings thorougly and settled for
> >> a setting that gives reasonable speed and transfer length.
> > 
> > This looks more like a signal integrity issue though.
> 
> It certainly does on the surface. However, when wrong data is
> delivered over the SPI bus (such as when I use wrong phase setting)
> the SPI controller happily delivers wrong data over PIO.
> 
> The failure I am seeing is that the pl330 DMA program which repeatedly
> waits for data from the SPI controller never finishes the read loop
> and does not signal the interrupt. It seems it also leaves some data
> in a FIFO somewhere so next command on the flash returns garbage and
> fails.

I observed something similar on MXS (mx28) SPI block. Do you use mixed
PIO/DMA mode perhaps ? Do you have the option to connect a bus analyzer?
I can probably offer you some tools, I'm in Prague ...

Best regards,
Marek Vasut
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