From: Gregory CLEMENT <gregory.clement@free-electrons.com>
To: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>,
        Mark Rutland <mark.rutland@arm.com>, Andrew Lunn <andrew@lunn.ch>,
        Russell King <linux@arm.linux.org.uk>,
        Jason Cooper <jason@lakedaemon.net>, Pawel Moll <pawel.moll@arm.com>,
        Ian Campbell <ijc+devicetree@hellion.org.uk>,
        linux-kernel@vger.kernel.org, devicetree@vger.kernel.org,
        Rob Herring <robh+dt@kernel.org>, Kumar Gala <galak@codeaurora.org>,
        Benoit Masson <yahoo@perenite.com>,
        linux-arm-kernel@lists.infradead.org,
        Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Subject: Re: [PATCH 4/4] ARM: dt: mvebu: ix4-300d: Add ECC properties to NAND flash
References: <1448709248-21177-1-git-send-email-sebastian.hesselbarth@gmail.com>
	<1448709248-21177-5-git-send-email-sebastian.hesselbarth@gmail.com>
	<20151129153548.304522af@free-electrons.com>
	<565C090D.4060006@gmail.com>
Date: Mon, 30 Nov 2015 15:22:02 +0100
In-Reply-To: <565C090D.4060006@gmail.com> (Sebastian Hesselbarth's message of
	"Mon, 30 Nov 2015 09:30:05 +0100")
Message-ID: <87a8pv5zzp.fsf@free-electrons.com>
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Hi Sebastian,
 
 On lun., nov. 30 2015, Sebastian Hesselbarth <sebastian.hesselbarth@gmail.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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