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Date:   Wed, 2 Nov 2022 09:12:27 +0200
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Subject: Re: Barebox / Kernel Omap ECC inconsistency?
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To:     Colin Foster <colin.foster@in-advantage.com>,
        linux-kernel@vger.kernel.org, linux-mtd@lists.infradead.org
Cc:     Pratyush Yadav <p.yadav@ti.com>,
        =?UTF-8?Q?Uwe_Kleine-K=c3=b6nig?= <u.kleine-koenig@pengutronix.de>,
        Krzysztof Kozlowski <krzk@kernel.org>,
        Vignesh Raghavendra <vigneshr@ti.com>,
        Richard Weinberger <richard@nod.at>,
        Miquel Raynal <miquel.raynal@bootlin.com>
References: <Y2FvB5D0K4MBii8N@COLIN-DESKTOP1.localdomain>
From:   Roger Quadros <rogerq@kernel.org>
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Hi Colin,

On 01/11/2022 21:09, Colin Foster wrote:
> Hello,
> 
> I'm trying to revive a product that runs on a Phytec OMAP 4460 SOM. I
> submitted a .dts RFC a month or so ago, and plan to perform the
> suggestions and resubmit, but I'm up against one main hurdle that seems
> to be related to flash OOB/ECC. (get_maintainers on
> drivers/mtd/nand/raw/omap2.c is how I got this email list)
> 
> Barebox has "native" support for the Phytec SOM:
> https://git.pengutronix.de/cgit/barebox/tree/arch/arm/boards/phytec-phycore-omap4460
> 
> It seems like Barebox is writing and expecting ECC bits to start at an
> offset of 12 bytes, while the kernel (and Barebox comments suggest) the
> ECC bytes should start at 2. I'm seeing this with
> `nanddump -n -o -l 0x41000 -f mtdxnanddump /dev/mtdx`
> 
> Barebox created partition with UBI (mtd3)
> ...
> 00000800  ff ff ff ff ff ff ff ff  ff ff ff ff 56 49 fd 17
> 00000810  b2 25 60 1a 42 1d eb 56  5d ff ff ff ff ff ff ff
> ...
> 
> Kernel created partition with UBI (mtd4)
> ...
> 00000800  ff ff 07 73 04 ac 57 6b  9b 1f 92 49 ab e0 b9 ff
> 00000810  ff ff ff ff ff ff ff ff  ff ff ff ff ff ff ff ff
> ...
> 
> 
> My question: 
> 
> Am I right to assume this is an issue in Barebox? Perhaps this is just a

I'm guessing so. Both u-boot and Linux for OMAP put the ECC bytes right
after the Bad block marker which is 2 bytes.

https://elixir.bootlin.com/linux/latest/source/drivers/mtd/nand/raw/omap2.c#L1729
https://elixir.bootlin.com/linux/latest/source/drivers/mtd/nand/raw/omap2.c#L134

> bug that has been fairly dormant for 15 years. If that is the case, I
> assume there's probably no hope in getting this mainlined, and "native"
> barebox support is just a ruse.
> 
> If that isn't the case, is there a hidden "shift OOB by 10" config
> option that I'm missing? Or am I interpreting this data incorrectly?
> 
> 
> Any suggestions would be greatly appreciated.

You should fix the OMAP NAND driver/config in Barebox to match that
with Linux OMAP NAND driver if you want them to run on the same system.

cheers,
-roger