linux-kernel - Re: [PATCH linux-next v5 3/5] mtd: spi-nor: allow to tune the number of dummy cycles

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Message-Id: <201508261639.02377.marex@denx.de>
Date:	Wed, 26 Aug 2015 16:39:02 +0200
From:	Marek Vasut <marex@...x.de>
To:	Cyrille Pitchen <cyrille.pitchen@...el.com>
Cc:	nicolas.ferre@...el.com, broonie@...nel.org,
	linux-spi@...r.kernel.org, dwmw2@...radead.org,
	computersforpeace@...il.com, zajec5@...il.com, beanhuo@...ron.com,
	juhosg@...nwrt.org, shijie.huang@...el.com, ben@...adent.org.uk,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	devicetree@...r.kernel.org, robh+dt@...nel.org, pawel.moll@....com,
	mark.rutland@....com, ijc+devicetree@...lion.org.uk,
	galak@...eaurora.org, linux-mtd@...ts.infradead.org
Subject: Re: [PATCH linux-next v5 3/5] mtd: spi-nor: allow to tune the number of dummy cycles

On Wednesday, August 26, 2015 at 02:30:25 PM, Cyrille Pitchen wrote:
> The number of dummy cycles used during Fast Read commands can be reduced
> to improve transfer performances. Each manufacturer has a dedicated set of
> registers to provide the memory with the exact number of dummy cycles it
> should expect. Both the memory and the (Q)SPI controller must agree on
> this number of dummy cycles.
> 
> The number of dummy cycles can be found into the memory datasheet and
> mostly depends on the SPI clock frequency, the Fast Read op code and the
> Single/Dual Data Rate mode.
> 
> Probing JEDEC Serial Flash Discoverable Parameters (SFDP) tables would
> only provide the driver with a high enough number of dummy cycles for each
> Fast Read command to be used for all clock frequencies: this solution
> would not be optimized.
> 
> Signed-off-by: Cyrille Pitchen <cyrille.pitchen@...el.com>

Acked-by: Marek Vasut <marex@...x.de>

Best regards,
Marek Vasut
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