Re: Plan for adding XD support in mtd layer

["Jörn Engel" <joern@logfs.org>]

Hello Maxim

On Wed, 25 November 2009 15:20:58 +0200, Maxim Levitsky wrote:
>
> Currently jmicron support is found in aspire one.
> My acer has ricoh device I know how works.

Those are card readers built into notebooks, right?  How are they
attached?  Via PCI or USB?

> Other that work of Alex Dubov, I need to write the code, but I don't
> want to repeat his mistake and write code that isn't accepted on basis
> of lack for fitness in existing subsystems.


> > > -> I need new mtd_info member for at least for card identification, and
> > > will be nice to have zone/block/page size
> > > This will be used by FTL and mtdchar to be exported to user space
> > 
> > Block and page size already exist as mtd->erasesize and mtd->writesize
> > respectively.  I'm not sure whether the zone size should become part of
> > the mtd interface - it looks more like a property of the ftl.
> You didn't understand me.
> I can't nether write nor erase individual blocks (writing is technically
> possible, but is disallowed by recent XD spec (this is what Alex Dubov
> says)
> 
> However I can _read_ individual sectors
> sector is 512 bytes, block is usually around 32 sectors.

It has been a while since I looked at the spec, but I believe there are
two parts to it.  The flash hardware allows block erases, sector reads
and sector writes.  On top of that you have the FTL that adds further
restrictions.

If you use you xD card without the FTL, as a raw MTD device, you can do
almost anything you want.  Format it with JFFS2, for example.  But if
used _with_ the FTL, that card now has a corrupt format and may be
unusable.

Or is the FTL already implemented in the card reader hardware?

> > What userspace programs would need this information?  I can imagine some
> > sort of xd_format or mkxd in case the card has been corrupted or used
> > raw.  Anything else?
> 
> I can imagine a format application, a rescue application, and an debug
> application that will show how healthy is the card.

Format and rescue certainly make sense.  I'm not sure how a debug
application would measure the health, but maybe that's possible as well.

> There are actually two pieces of the data.
> One is an ID, a serial number that can be used for example by udev for
> permanent mapping.

Ok, makes sense.

> Other is the media type, and this has to be used to know the sizes of
> sectors, zones, pages, how many spares there are etc...

That would be available when using mtdchar or mtdblock to read the
device.  Which ought to be enough for format, rescue and debug, I
believe.

> ECC corecting will be done in the base mtd driver, but userspace
> application will be able to determine if block is good or bad.
> If it is good, it can use oob information to determine of ECC correction
> was applied or not, and report overall health of the card.

With mtdchar it is possible to do ECC correction in userspace as well.
Not that I would consider it a good idea, but the information is
certainly available and can be controlled if a compelling reason can be
found.

Jörn

-- 
Invincibility is in oneself, vulnerability is in the opponent.
-- Sun Tzu