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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <201507220933.19752.marex@denx.de>
Date:	Wed, 22 Jul 2015 09:33:19 +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 09:30:54 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.

> However, if this was not tied to the particular slave setting picked
> in the current DT a formula would be needed that translates arbitrary
> client settings to transfer size limit and there would be need to
> somehow get the client settings to the formula in the dmaengine
> driver.
> 
> Thanks
> 
> Michal

Best regards,
Marek Vasut
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/