linux-kernel - Re: [PATCH 4/7] Documentation: mtd: add a DT property to set the latency code of Spansion memory

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Message-ID: <55ACBE1B.6050507@atmel.com>
Date:	Mon, 20 Jul 2015 11:23:39 +0200
From:	Cyrille Pitchen <cyrille.pitchen@...el.com>
To:	Marek Vasut <marex@...x.de>
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 4/7] Documentation: mtd: add a DT property to set the
 latency code of Spansion memory

Hi Marek,

Le 16/07/2015 19:44, Marek Vasut a écrit :
> On Thursday, July 16, 2015 at 05:27:51 PM, Cyrille Pitchen wrote:
> 
> Hi!
> 
>> Both the SPI controller and the NOR flash memory need to agree on the
>> number of dummy cycles to use for Fast Read commands. For Spansion
>> memories, this number of dummy cycles is not given directly but through a
>> so called "latency code".
>> The latency code can be found into the memory datasheet and depends on the
>> SPI clock frequency, the Fast Read op code and the Single/Dual Data Rate
>> mode.
> 
> Shouldn't you be able to derive the latency code from the above information,
> which you already know then ?
Yes I agree with you; this could have been done adding static tables inside the
driver instead of creating a new DT property dedicated to Spansion memories.

When I wrote this patch, I had a close look at the s25fl512s datasheet but only
overviewed few datasheets for other Spansion QSPI flash memories. So I don't
know whether a single latency code table could be shared among all Spansion
memories or many tables should be added to support different memory models.

That's why I've chosen to add a dedicated DT property to support Spansion
memories as it avoids to add tables to guess the proper latency code to be
used. I thought it would be more flexible.

Maybe I will remove the support of Spansion QSPI memories from this series for
now. Their support can still be implemented later.

Anyway, thanks for your review :)

> 
> Best regards,
> Marek Vasut
> 

Best Regards,

Cyrille
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