[PATCH v3 00/10] About the SLC/MLC

[Gupta, Pekon]

> From:  Huang Shijie
> On Mon, Aug 26, 2013 at 02:41:53PM +0200, Thomas Petazzoni wrote:
> > Dear Huang Shijie,
> >
> > On Mon, 26 Aug 2013 17:36:38 +0800, Huang Shijie wrote:
> > > In current mtd code, the MTD_NANDFLASH is used to represent both the
> > > SLC nand MLC(including the TLC). But we already have the
> MTD_MLCNANDFLASH
> > > to stand for the MLC. What is worse is that the JFFS2 may run on the MLC
> > > nand with current code. For the reason of READ/WRITE disturbance, the
> JFFS2
> > > should runs on the SLC only,
> >
> > Pardon the probably very silly question, but would you mind giving more
> > details about why JFFS2 is not appropriate on MLC flashes? Is there
> > anything that UBI/UBIFS does that JFFS2 isn't doing to take into
> > account read/write disturbance?
> I try to explain it.
> 
> For the UBIFS, it will writes the page(including the oob) only one time;
> but for jffs2, it may writes the page(including the oob) twice, one for the
> marker, one for the real data.
> 
> For the MLC, the write disturbance will cause some bitflips in this
> page. Since you write a page twice, so in the jffs2, you will meet
> uncorrectable
> ECC error.
> 
But, doesn't JFFS2 checks for the blank page before second-write of data ?
UBI does it here..
File: $KERNEL/drivers/mtd/ubi/io.c
@@ubi_io_write (... )
[...]
	err = ubi_self_check_all_ff(ubi, pnum, offset, len);

So, isn't it better to add this check in JFFS2 code so that its more
bit-flips tolerant ?
This way bit-flips caused by first write to OOB (cleanmarker) would be
caught before using that page for data write. And so MLC should also be
good for JFFS2..

with regards, pekon