[PATCH V3 3/6] MTD : add the database for the NANDs

[Brian Norris]

Hi,

I see nothing has happened with this thread recently. It doesn't
deserve to die though.

On Thu, Mar 31, 2011 at 10:17 AM, Huang Shijie <shijie8 at gmail.com> wrote:
> 2011/3/31 Artem Bityutskiy <dedekind1 at gmail.com>:
>>> > If you have new chips to support in the future, you should add them in
>>> > drivers/mtd/nand/nand_ids.c and not keep this file.
>>> >
>>> The data structure  nand_flash_dev{} does not contain enough information.
>>> So I want to the nand_device_info{} to replace it in future.
>>
>> Just add this information, if it is of generic nature (like SLC/MLC
>> flag, required ECC strength, etc).

Are SLC/MLC and ECC strength necessary to track? I don't see a good
benefit to cost ratio of trying to detect ECC strength especially,
since the levels specified in data sheets vary without much pattern
and nobody provides a way for decoding this from ID; do you really
want to have to make separate chip entries for every single chip that
comes around?

>>> > I still do not understand why this would be needed, is it because the generic
>>> > code does not provide enough informations for your driver?
>>> >
>>> yes.
>>>
>>> IMHO, the generic code is somehow trapped in a wrong way. :(

I may agree, but can you be more specific on the trap?

>>> Paring the id bytes is not sufficient to get all the information you
>>> need which is faced by me.

What's an alternative to "paring the id bytes"?

>>> What's more, I think the paring code is ugly, see the nand_get_flash_type().
>>
>> You are welcome to fix this. There is _a lot_ of ugly code in MTD
>> because no one loves it. Give it some love :-)

While I agree that a lot of this is ugly, it is mostly a matter of
necessity. NAND manufacturers do not have a standard (ONFI doesn't
really count, since there's basically 1 manufacturer using it), and so
the most "generic" code is to have different code paths for different
manufacturers (often with exceptions to each rule, since even a single
manufacturer changes its standards arbitrarily). Then you find
manufacturers like Toshiba that recently don't have any (published)
pattern at all for detecting OOB size generically.

Thus, it seems to me like we will need some form of the approach
provided by Huang. As I've found, there are some things that just
can't be decoded from the ID these days, so our ID table will need to
be able to track:
* full ID string (not just the 2nd byte "Device ID")
* relevant bad block scanning options

FWIW, we already implement an exception table in our own driver that
includes the above 2 items, for chips that can't be handled with the
table/detection structure as-is. We don't particularly need SLC/MLC
but I don't object to recording it if we can determine it reliably,
and while ECC level could be useful, it is difficult to discover
generically, as I mentioned above.

>>> Why not create a new database which contains all the necessary
>>> information for a nand, and can be easy
>>> find by the id bytes as the keyword?
>>
>> You can create this database by extending/improving/cleaning up the
>> existing code base with a nice series of patches.
>>
> ok. I will try to fix the generic code before my driver is submitted.

What happened to this statement? I see that your driver was submitted,
but no efforts were made for chip detection cleanup. Were you
satisfied with the current detection?

While we're on the subject, I'll direct your attention to this NAND
data table that I've worked on. It should provide a decent summary of
most of the data sheets I have sorted through. It should also show you
that certain things are going to be very hard to detect (e.g., ECC
level). It should also show that while some chips are not supported by
standard code (e.g., weird bad block scanning features that haven't
been supported, non-standard OOB sizes with no given pattern in the
datasheets), the vast majority of the chips I've come across should be
detected properly:

http://linux-mtd.infradead.org/nand-data/nanddata.html

And of course, please contribute to
git://git.infradead.org/mtd-www.git if you have additions or edits for
the table. It's not perfect, but it can help for sorting through
different chips.

Brian