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Date: Mon, 6 Apr 2009 23:25:08 +1200
From: Andrew Turner <andrew@fubar.geek.nz>
To: Stanislav Sedov <stas@FreeBSD.org>
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Cc: freebsd-embedded@freebsd.org, freebsd-geom@freebsd.org
Subject: Re: FreeBSD NAND flash driver
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On Mon, 6 Apr 2009 12:24:10 +0400
Stanislav Sedov <stas@FreeBSD.org> wrote:
> > It is not usable yet as the write will not perform any deletes from
> > the device, either the file system or another geom will have to
> > issue a BIO_DELETE followed by BIO_WRITE's to write to the disk.
> > This is done to support NAND flash aware file systems.
> >
> 
> So, for ordinary file systems we're going to use the special geom
> layer that will sit above the nand(8) device and perform BIO_DELETE
> operations when required?
Yes, this is intentional as NAND flash is split up to blocks. The
blocks are then split into pages. You have to erase the entire block at
a time but can write pages as required. A file system that knows about
this difference will be able to talk to nand(8) directly.

>  
> > TODO:
> >  * ECC support.
> >  * Add GEOM attributes to get information about the NAND device out,
> >    eg. Block size, OOB data, etc.
> >  * Test the erase code.
> >  * Add support for real hardware.
> >  * Read the parameter page on parts that support it to get the
> > required information.
> > 
> > Andrew
> > 
> > [1]
> > http://fubar.geek.nz/files/freebsd/nand/freebsd-nand-20090405.tar.gz
> 
> What about putting this information to the wiki? Seems like a good
> start for anyone who'll be working on the real hardware.
> And thanks again for the great work!
I'm planning on doing this. I'm currently cleaning up the code before
getting the first hardware driver written.

Andrew