An FAQ would be nice, an example would be nicer and a patch file would be
perfect. 

I too have the need to make a 2.6.20 / Yaffs2 setup play with an earlier
version (2.4.21/ original yaffs) I am struggling to get this to work. When I
upgrade a device to new firmware, I have to save the NAND contents, bring up
the new system (which trashes the NAND) and then restore the files. - Not
always possible though due to space constraints.

Thanks (hopefully)

Steve



On 8/8/07 4:46 PM, "ian@brightstareng.com" <ian@brightstareng.com> wrote:

> Rick,
> 
> On Wednesday 08 August 2007 15:05, Rick Bronson wrote:
>>   If yaffsVersion is never set to 2 (ie. always set to 1),
>> does that mean that a partition that was written with ancient
>> yaffs1 code on a 2.4 kernel will be able to be read/written
>> using modern yaffs2 code and a 2.6.22 kernel with a 512/16
>> part?
> 
> The yaffsVersion variable, displayed as isYaffs2 in /proc/yaffs,
> shows which yaffs methods are being used. So called Yaffs1
> methods are used when the underlying device is a small-page
> (512) NAND chip. Yaffs2 methods are used when the underlying
> device is large-page (2k).  Yaffs operates differently on these
> two types of NAND.
> 
> The "yaffs2" codebase at cvs.aleph1.co.uk:/home/aleph1/cvs
> supports both page sizes, both sets of methods.  When it runs
> with a small-page device, it runs much like the original "yaffs"
> codebase.
> 
> The format or layout of the tags and MTD's ECC is really a
> separate issue. There are various formats depending mainly on
> the MTD vintage and configuration choices.
> 
> With 2.4 MTD, and 2.6 pre 2.6.17, Yaffs may influence the layout
> using the nand_oobinfo struct in yaffs_mtdif.c.  But with newer
> kernels (post 2.6.17) MTD defines the layout using
> nand_ecclayout in nand_base.c, or the platform NAND mapping
> driver, and Yaffs just goes along with the MTD's 'autoplace'
> policy.
> 
> Compatibility: If you build the "yaffs2" codebase for a post
> 2.6.17 kernel with CONFIG_YAFFS_9BYTE_TAGS set, and you are
> using a small-page NAND chip, the layout can be made compatible
> with an older scheme, but you have to have MTD's nand_ecclayout
> defined appropriately -- use the older implementation as a
> reference to derive the tags/ECC byte ordering that is/was used,
> then define a compatible nand_ecclayout 'autoplace' policy for
> use on the post 2.6.17 platform.
> 
> [We need a Yaffs FAQ, don't we]
> 
> -imcd
> 
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