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 15:22:02 +0100
From:	Gregory CLEMENT <gregory.clement@...e-electrons.com>
To:	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
Cc:	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	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>,
	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

Hi Sebastian,
 
 On lun., nov. 30 2015, Sebastian Hesselbarth <sebastian.hesselbarth@...il.com> wrote:

> 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.

So for now, I don't apply it.

Thanks,

Gregory

-- 
Gregory Clement, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com
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