Clarification on multiple mtdram devices

Clarification on multiple mtdram devices

[MikeW]

>From a (much) earlier post, I note that the mtdram driver can emulate
several /dev/mtd's by "loading the driver more than once".

Does this mean modprobing *once* but then setting up multiple
device nodes with the same major number and different minor numbers ?

I presume this also implies that each device must have the same size & erasesize.

Regards,
MikeW

Re: Clarification on multiple mtdram devices - HowTo

[MikeW]

MikeW <mw_phil <at> yahoo.co.uk> writes:

> 
>From a (much) earlier post, I note that the mtdram driver can emulate
>several /dev/mtd's by "loading the driver more than once".
> 
>Does this mean modprobing *once* but then setting up multiple
>device nodes with the same major number and different minor numbers ?
> 
>I presume this also implies that each device must have the same
size & erasesize.
> 
> Regards,
> MikeW

Found out about doing this here:
http://electrons.psychogenic.com/modules/wordpress/rants/
2005/08/28/13/linux-on-the-go-exploring-ipaq-options.html

(I would like a section doing this properly on the MTD website FAQ
written by an authoritative person - please !)
>>>>>
To start we load a few modules, creating a fake 32M flash device
 in RAM and ensure we have appropriate /dev/ entries:

# modprobe mtdcore
# modprobe mtdram total_size=32768 erase_size=256
# mkdir /dev/mtdblock ; for i in 0 1 2 3 ;
 do mknod /dev/mtdblock/$i b 31 $i; done

Then we write the contents of one of the JFFS2 images
to the MTD RAM device, and take a look:

# dd if=gpe-image-h3600-20050407124742.rootfs.jffs2 of=/dev/mtdblock/0
# mkdir -p /mnt/ipaq/
# mount -t jffs2 /dev/mtdblock/0 /mnt/ipaq
# cd /mnt/ipaq; ls;

The output will be something like:

	bin  boot  dev  etc  home  lib  media  mnt  proc  sbin
  sys  tmp  usr  var
<<<<

Re: Clarification on multiple mtdram devices - HowTo

[Josh Boyer]

On Wed, 2007-03-21 at 12:39 +0000, MikeW wrote:
> 
> Found out about doing this here:
> http://electrons.psychogenic.com/modules/wordpress/rants/
> 2005/08/28/13/linux-on-the-go-exploring-ipaq-options.html
> 
> (I would like a section doing this properly on the MTD website FAQ
> written by an authoritative person - please !)
> >>>>>
> To start we load a few modules, creating a fake 32M flash device
>  in RAM and ensure we have appropriate /dev/ entries:
> 
> # modprobe mtdcore
> # modprobe mtdram total_size=32768 erase_size=256
> # mkdir /dev/mtdblock ; for i in 0 1 2 3 ;
>  do mknod /dev/mtdblock/$i b 31 $i; done
> 
> Then we write the contents of one of the JFFS2 images
> to the MTD RAM device, and take a look:
> 
> # dd if=gpe-image-h3600-20050407124742.rootfs.jffs2 of=/dev/mtdblock/0
> # mkdir -p /mnt/ipaq/
> # mount -t jffs2 /dev/mtdblock/0 /mnt/ipaq
> # cd /mnt/ipaq; ls;

This is about creating a single MTD with mtdram and effectively using
that for loopback.  You had asked about creating multiple MTDs with
mtdram.  So does this fully answer your question, or?

/me is a bit confused.

josh

Re: Clarification on multiple mtdram devices - HowTo

[MikeW]

Josh Boyer <jwboyer <at> linux.vnet.ibm.com> writes:

> 
> 
> This is about creating a single MTD with mtdram and effectively using
> that for loopback.  You had asked about creating multiple MTDs with
> mtdram.  So does this fully answer your question, or?
> 
> /me is a bit confused.
> 
> josh

I wanted to create more than one MTD in RAM to emulate a board
with Flash memory split into several partitions, mtd0..n, mtdblock0..m

It's not immediately clear what (if any) relationship there is
between device numbers and partitions, and there's not much on the 
MTD site.

I noted the existence of mtdram, but then wanted to know how best
to use it.

I noted that mtdram only appeared to be capable of creating one device,
so was looking for a way of creating several devices (mtd0...n).
I looked in the driver code but it confirmed that only one mtd
would exist, AFAICS.

>From the quoted item it looks as if you can create several mtds
by creating one mtdram and then splitting it up using mtdblock.

It would be useful if there was a proper 'howto' on this subject
on the website, since I have only been able to piece this
together by much searching.

So can some mtd drivers (mtdblock) subdivide mtd devices provided by
other drivers, for example ?

I have been looking for some kind of overall 'concept of operation'
but without much luck ATM !

If I *do* manage to put all the pieces together I will willingly
write it up on the site !

Regards,
MikeW