[maemo-users] [maemo-users] Formating RSMMC in JFFS2

From: Nils Faerber nils.faerber at kernelconcepts.de
Date: Mon Jan 16 15:32:07 EET 2006
Hash: SHA1

Frantisek Dufka schrieb:
> What are you trying to achieve? jffs works directly with flash memory by
> programming/erasing the flash, you can't do this with mmc card. MMC card
> is an ordinary block device and it should do wear leveling itself in
> some lower layer. You surely could mount such jffs image somehow but
> there is no point in doing that except when you already have jffs image
> and need data from it. And for this you need another module which could
> emulate the flash (=MTD device) over block device.

In fact JFFS2 could in theory work on an MMC as it accesses the Flash
thorugh the MTD block device layer.
It currently does not work because it asks the MTD layer for some
parameters of the MTD device, like eraseblocksize. I am pretty sure that
JFFS2 could be tweaked to use defaults if the MTD parameters are missing
like they of course do on an MMC card. Yet this has not been done yet
and the only (quite useless) way to have JFFS2 access to an ordinary
block device is the already mentioned mtd block emulation device (which
in fact does not much more than "emulating" the mtd parameters).

But using JFFS2 on an MMC card does not help for anything else than
compression - wear levelling should already be done by the card itself
and double wear levelling by card + JFFS could even be more fatal than

> Frantisek
  nils faerber

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