gluebi and flash file systems using the OOB

gluebi and flash file systems using the OOB

[Diego COSTE]

Hello,

I hope I don't ask a question already answered, but I didn't find an
easy way to search the mailing list.

The HW NAND controller we use automatically handles the ECC and uses
all of the OOB for that.

I saw that UBI and UBIFS do not use OOB, and therefore are compatible
with that HW and its SW driver.

But we also have to use alternate flash file systems (JFFS2, YAFFS2).
Unfortunately these file systems use the OOB and therefore can't
directly work with the HW we use.

Then I saw that there is gluebi that re-exports a MTD, and that it is
possible to use JFFS2 on top of it.

So here are the questions:
Does gluebi provide an OOB emulation so that we can use *any* flash file
system that uses the OOB ?
Or do we have to force the FS not to use the OOB ?

Thanks for your kind help,

Diego

Re: gluebi and flash file systems using the OOB

[Shmulik Ladkani]

Hi Diego,

On Wed, 25 Jul 2012 12:33:53 +0200 Diego COSTE <diego.coste@st.com> wrote:
> But we also have to use alternate flash file systems (JFFS2, YAFFS2).
> Unfortunately these file systems use the OOB and therefore can't
> directly work with the HW we use.

You should consider using UBIFS if possible.

> Then I saw that there is gluebi that re-exports a MTD, and that it is
> possible to use JFFS2 on top of it.

Gluebi exports a virtual MTD for each UBI volume.
This MTD's type is MTD_UBIVOLUME.
It is not a NAND MTD (MTD_NANDFLASH) - it does not have bad blocks,
pages, and oob part. It "resembles" NOR flash.

> Does gluebi provide an OOB emulation so that we can use *any* flash file
> system that uses the OOB ?

No.

Note JFFS2 works on top of NOR MTDs (and as such, doesn't use OOB).
So it *should* work on an MTD_UBIVOLUME as well.

However if jffs2 is mounted on MTD_NANDFLASH, it utilizes the OOB.

I remember reading something about inband tags for yaffs2.
Don't know the exact status of this; I think you should take a look.

Regards
Shmulik

Re: gluebi and flash file systems using the OOB

[Artem Bityutskiy]

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On Wed, 2012-07-25 at 12:33 +0200, Diego COSTE wrote:
> So here are the questions:
> Does gluebi provide an OOB emulation so that we can use *any* flash file
> system that uses the OOB ?
> Or do we have to force the FS not to use the OOB ?

No, OOB is not available on gluebi emulated MTD devices. However, since
it is emulation layer, and UBI itself does not care about what is in
OOB, I do not see why you could not add OOB support to gluebi.

-- 
Best Regards,
Artem Bityutskiy

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