Re: [RFC/PATCH 2/3] NAND multiple plane feature

["Jörn Engel" <joern@logfs.org>]

On Wed, 28 May 2008 14:08:01 +0100, Alexey Korolev wrote:
> 
> As NAND multiple plane architecture assumes simultaneous write/erase of
> several pages/blocks at the same time, we have to modify page/eraseblock
> sizes and report modified size to upper layers. In other words physical
> erase block size/ page size != reported erase block size/ page size.
> For example if we have dual plane device we have to extend erase block
> size and page size in 2 times. 

Before actually reading the datasheets (just now) I had hoped that
manufacturers would provide us several independent read/write/erase
units per chip and allow software to deal with each plane as if it was a
seperate chip.  _That_ would have been really useful.  And for NOR
flashes, Intel has already shown how to do it.

But hoping for manufacturers to get it right rarely works - it certainly
didn't work in this case.  As it seems, we can either program two planes
in a weird lock-step process or ignore the feature.  And the lock-step
variant isn't useful for much more than doubling/quadrupling the
erasesize and writesize.  With all the disadvantages that brings. :(

Speaking about the disadvantages, if the dual plane feature is
enabled/disabled across reboots and erase size or write size changes,
we're in for a lot of fun from the filesystem size.  F.e. JFFS2 will
experience data loss when erase size isn't stable.

Jörn

-- 
All models are wrong. Some models are useful.
-- George Box