Re: NAND Flash device driver

[Gary Thomas <gary at mlbassoc dot com>]

Alexey Shusharin wrote:
> Ð ÐÑÑ, 18/12/2007 Ð 10:13 +0100, Andrew Lunn ÐÐÑÐÑ:
>> On Tue, Dec 18, 2007 at 10:03:11AM +0600, Alexey Shusharin wrote:
>>> ?? ??????, 10/12/2007 ?? 19:01 +0600, Alexey Shusharin ??????????:
>>>> Hi,
>>>>
>>>> This patch adds a NAND Flash device driver to flash V1 branch.
>>>>
>>>> Currently it supports 8-bit NAND flash with 256/512 page size and has
>>>> implemented software ECC and simple bad block management algorithms.
>>>>
>>>> I've tested it with SAMSUNG K9F5608U0D.
>>>>
>>>> Best regards
>>>> Alexey Shusharin
>>>>
>>> Hi guys!
>>>
>>> What's wrong with this patch? Why you didn't answer?
>> I've never worked with a NAND device, so i did not feel too happy to
>> look at this patch. I hope one of the other maintainers has the
>> necessary background.
>>
> Hi,
> Thanks for answer.
> 
>> Having said that, i took a quick look at the code. I have some general
>> questions about NAND devices and drivers.
>>
>> You have the ECC and bad block management code integrated with the
>> package. Is this specific to the Samsung device? I'm wondering if this
>> should be separated out, either into a new package, or made part of
>> io/flash with some CDL to control it. It then makes it possible for
>> other manufactures devices to use this code.
> 
> I didn't check all NAND devices, of course. But devices which i know
> have identical memory arrangements and general access methods. They
> differs only access times which is adjusted by platform code. Moreover,
> Linux NAND driver doesn't distinguish between different manufacturers.
> So i think this driver should work with different manufacturers devices.
> 
> If this statement is true the ECC and bad block management algorithms
> depend of NAND page size only. This driver support only small page (256
> or 512 bytes), but can be modified to support large page in the future
> (device with large page has other command set).
> 
> Other issue is 16-bit bus width support. It's not difficult to add this
> feature (add 3 small functions), but i cannot test it because have 8-bit
> flash only.
> 
>> You say this is not compatible with Linux. How much effort is required
>> to make it compatible? A lot of people use eCos for RedBoot, booting
>> Linux. In this situation it is useful to be compatible with Linux.
> 
> Unfortunately Linux NAND driver has complex bad block management
> algorithm and the best way to make driver compatible with Linux - get
> code from it (this is that u-boot does). Therefore if i use other bbm
> algorithm, it doesn't matter to use the same ECC algorithm, more so i
> didn't find its description.
> 
> You can find more information about Linux NAND driver there:
> http://www.linux-mtd.infradead.org/doc/nand.html
> http://www.linux-mtd.infradead.org/tech/mtdnand/index.html
> 
> There are other reasons in using especial bbm algorithm.
> eCos flash API doesn't have methods to works with NAND speciality (write
> to spare area, check bad blocks and etc.) and RedBoot doesn't support
> this features too. This driver hides NAND flash particularity and makes
> it transparent for flash API and RedBoot FIS.
> 
> Maybe somebody has other opinion. You are welcome! ;-)

I've not had time to review this, but how different is it from
the existing Toshiba NAND device driver?


-- 
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Gary Thomas                 |  Consulting for the
MLB Associates              |    Embedded world
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