Re: [PATCH 0/2] drivers/mtd: add a core

[Sascha Hauer <s.hauer@pengutronix.de>]

On Tue, Dec 13, 2011 at 11:51:10AM +0100, Robert Jarzmik wrote:
> Sascha Hauer <s.hauer@pengutronix.de> writes:
> 
> > I created the nand_oob device mainly for debugging purposes. It can be
> > convenient to be able to see the oob data. As this has no practical
> > use besides debugging it can be easily replaced with an interleaved
> > data/oob device. The oob device is quite inconvenient to use anyway
> > since it requires some calculating to get the oob data for a given
> > page.
> True. What we would need to make it simple :
>  - have arithmetic expressions in hush

Uhh, have you looked at the code? You can hardly even fix a bug
without introducing another one :(

>  - have a "dd" command with options skip,bs,count
>    => that is actually a requirement to flash (as cp uses blocks of 4096, while
>    flash with oob wants block of writesize+oobsize which are seldom multiples of
>    512).

I don't know much about disk-on-chip. Do you really have to write
the images completely with oob data?

However, I don't like the idea that we have to use a special command
to flash an image.

The Nand flashes we support all can have bad blocks. For this we have
the 'bb' devices. So currently what you see in /dev/ is:

crw-------     262144 dev/nand0.barebox.bb
crw-------     131072 dev/nand0.bareboxenv.bb
crw-------    2097152 dev/nand0.kernel.bb
crw-------   64552960 dev/nand0.root.bb
crw-------   64618496 dev/nand0.root
crw-------    2097152 dev/nand0.kernel
crw-------     131072 dev/nand0.bareboxenv
crw-------     262144 dev/nand0.barebox
cr--------    2097152 dev/nand_oob0
crw-------   67108864 dev/nand0

/dev/nand0 is the full raw nand device. /dev/nand0.barebox is an example
for a partition on this device (also raw, with bad blocks).
/dev/nand0.barebox.bb is this partition, but this device automatically
skips bad blocks and this also makes sure that only writesize aligned
accesses go to the underlying layers. This way we can simply do a
'cp image /dev/nand0.kernel.bb' or a 'tftp barebox
/dev/nand0.barebox.bb'

Would that be suitable for disk-on-chip aswell?

> 
> I was thinking that a "dd" command would be handy. Would you accept it in
> barebox ?

If it can do something else than the memcpy command, why not? The memcpy
command is quite flexible and not limited to memory, see here:

http://wiki.barebox.org/doku.php?id=commands:memcpy

Sascha

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