From mboxrd@z Thu Jan  1 00:00:00 1970
From: Marek Vasut <marek.vasut@gmail.com>
Date: Wed, 14 Sep 2011 00:41:29 +0200
Subject: [U-Boot] [PATCH 5/5] NAND: Add scrub.quiet command option
In-Reply-To: <4E6FD793.4010906@freescale.com>
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	<201109130302.16991.marek.vasut@gmail.com>
	<4E6FD793.4010906@freescale.com>
Message-ID: <201109140041.30150.marek.vasut@gmail.com>
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[...]

> > ROM when loading firmware, copies back
> > the value at metadata[0] to BI offset in page data. The following figure
> > shows how the factory bad block marker is preserved.
> 
> ...this is insane.  It seems that they want you to swap this byte even
> in good blocks, so that you put the byte of real data that should go
> somewhere in the middle of the last 512-byte ECC chunk at offset zero in
> the page.  This means that it will show up as a bad block when normal
> (but new-layout-using) software looks at it, which is why you need
> scrub.  Ew.
> 
> How many blocks are being loaded by this mechanism?  Just block zero
> (which is normally supposed to be guaranteed good anyway...)?  Or
> multiple blocks?

The first block, then the 64th block, 128th block and 192th block (in default 
layout).
> 
> Any chance you could blow the NAND_MEMBLOCK_MARKER_RESERVE fuse? :-)

No, they are one-time programable. Delivering a "damaged" chip isn't a good 
practice.

> Otherwise, I guess you do need to scrub.  Have you complained to
> Freescale sales/support?

In fact no. The BootROM is "broken" and I doubt they will be willing to do 
anything about it.

> 
> > But we want to write a block in our own format, so we need to scrub (wipe
> > the block completely).
> 
> Erase always wipes the block completely, if it erases at all.  Scrub in
> this context just means that U-Boot ignores the bad block indications
> (marker or table).  Otherwise it would avoid erasing bad blocks, so that
> they stay bad, and you won't have scrubbed the entire region requested.
> 
> >> I work for the PowerPC side of Freescale, in case you're wondering why
> >> I'm unfamiliar with this. :-)
> > 
> > Interesting ... does everyone work for the PowerPC side of Freescale or
> > is there some other reason why I never met anyone working for the ARM
> > side of Freescale ? ;-)
> 
> They exist, but don't seem to engage Open Source development communities
> to the same degree.
> 
> -Scott

Cheers