linux-kernel - Re: [PATCH 4/4] ARM: dt: mvebu: ix4-300d: Add ECC properties to NAND flash

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Date:	Mon, 30 Nov 2015 09:30:05 +0100
From:	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
To:	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
Cc:	Mark Rutland <mark.rutland@....com>, Andrew Lunn <andrew@...n.ch>,
	Russell King <linux@....linux.org.uk>,
	Jason Cooper <jason@...edaemon.net>,
	Pawel Moll <pawel.moll@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
	Rob Herring <robh+dt@...nel.org>,
	Kumar Gala <galak@...eaurora.org>,
	Gregory Clement <gregory.clement@...e-electrons.com>,
	Benoit Masson <yahoo@...enite.com>,
	linux-arm-kernel@...ts.infradead.org,
	Ezequiel Garcia <ezequiel.garcia@...e-electrons.com>
Subject: Re: [PATCH 4/4] ARM: dt: mvebu: ix4-300d: Add ECC properties to NAND
 flash

On 29.11.2015 15:35, Thomas Petazzoni wrote:
> Adding Ezequiel Garcia in Cc.
>
> On Sat, 28 Nov 2015 12:14:08 +0100, Sebastian Hesselbarth wrote:
>> The NAND device found on Lenovo ix4-300d uses 4-bit BCH ECC protection.
>> Add the corresponding properties to the NAND node.
>
> If the ONFI information from the NAND flash say that it requires 4 bits
> per 512, then there should be no need to add this information to the
> Device Tree as the pxa3xx_nand driver by default uses the ONFI
> information.

Thomas,

as said in the cover letter, this is also DT cleanup with barebox
bootloader in mind. I do not accept what Linux' pxa3xx_nand driver
is doing as a reference here ;)

> Those properties are only needed when for some reason the vendor has
> chosen to use a ECC strength that doesn't match with the one advertised
> by the flash in its ONFI information (either stronger or weaker). But
> in this case, your commit log is confusing, because it says that the
> "NAND device ... uses 4-bit BCH ECC protection". If it really does,
> then the patch is not needed :-)

I agree that if ONFI is already advertising 4/512 ECC (and it is), we
do not need the properties. Anyway, IIRC barebox does not yet properly
parse ONFI or at least it does not derive minimum ECC settings from it.

I'll have to have a closer look at barebox' ONFI parsing capabilites
and can live with this patch not applied even though it does no harm.

Sebastian

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