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

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Date:	Thu, 4 Jun 2015 01:03:09 +0200
From:	Marek Vasut <marex@...x.de>
To:	Michal Suchanek <hramrach@...il.com>
Cc:	Rob Herring <robh+dt@...nel.org>, Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Russell King <linux@....linux.org.uk>,
	Kukjin Kim <kgene@...nel.org>,
	Krzysztof Kozlowski <k.kozlowski@...sung.com>,
	Vinod Koul <vinod.koul@...el.com>,
	Dan Williams <dan.j.williams@...el.com>,
	David Woodhouse <dwmw2@...radead.org>,
	Brian Norris <computersforpeace@...il.com>,
	Han Xu <han.xu@...escale.com>, Mark Brown <broonie@...nel.org>,
	Geert Uytterhoeven <geert+renesas@...der.be>,
	" Rafał Miłecki" 
	<zajec5@...il.com>, Alison Chaiken <alison_chaiken@...tor.com>,
	Huang Shijie <b32955@...escale.com>,
	Ben Hutchings <ben@...adent.org.uk>,
	Knut Wohlrab <knut.wohlrab@...bosch.com>,
	"Bean Huo 霍斌斌 \(beanhuo\)" 
	<beanhuo@...ron.com>, "grmoore@...era.com" <grmoore@...era.com>,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-samsung-soc@...r.kernel.org, dmaengine@...r.kernel.org,
	linux-mtd@...ts.infradead.org, linux-spi@...r.kernel.org
Subject: Re: [PATCH 08/11] MTD: m25p80: Add option to limit SPI transfer size.

On Wednesday, June 03, 2015 at 11:26:41 PM, Michal Suchanek wrote:
> On sunxi the SPI controller currently does not have DMA support and fails
> any transfer larger than 63 bytes.
> 
> On Exynos the pl330 DMA controller fails any transfer larger than 64kb
> when using slower speed like 40MHz and any transfer larger than 128bytes
> when running at 133MHz.

This smells more like some corruption of the data on the bus or something
even more obscure.

> The best thing is that in both cases the controller can just lock up and
> never finish potentially leaving the hardware in unusable state.
> 
> So it is required that the m25p80 driver actively prevents doing
> transfers that are too large for the current driver state on a
> particular piece of hardware.
> 
> Signed-off-by: Michal Suchanek <hramrach@...il.com>
> 
> --
> 
> Update commit message and documentation text.
> ---
>  .../devicetree/bindings/mtd/jedec,spi-nor.txt      |  6 ++++++
>  drivers/mtd/devices/m25p80.c                       | 24
> ++++++++++++++++++++-- 2 files changed, 28 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/devicetree/bindings/mtd/jedec,spi-nor.txt
> b/Documentation/devicetree/bindings/mtd/jedec,spi-nor.txt index
> 2bee681..4e63ae8 100644
> --- a/Documentation/devicetree/bindings/mtd/jedec,spi-nor.txt
> +++ b/Documentation/devicetree/bindings/mtd/jedec,spi-nor.txt
> @@ -19,6 +19,12 @@ Optional properties:
>                     all chips and support for it can not be detected at
> runtime. Refer to your chips' datasheet to check if this is supported by
> your chip.
> +- linux,max_tx_len : With some SPI controller drivers possible transfer
> size is +                     limited. This may be hardware or driver bug.
> +                     Transfer data in chunks no larger than this value. +
>                     Using this option may severely degrade performance and
> +                     possibly flash memory life when max_tx_len is
> smaller than +                     flash page size (typically 256 bytes)

Will we need similar patch for all other SPI slave drivers, like SPI NAND ?

Best regards,
Marek Vasut
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