gpmi-nand driver and jffs2 support

[Huang Shijie]

于 2013年09月24日 20:53, Marek Vasut 写道:
> Hello Huang,
>
>> 于 2013年09月24日 17:50, Marek Vasut 写道:
>>> Hello Huang,
>>>
>>> Can you please explain what is the exact difference between the NAND
>>> layout when using JFFS2 in FSL 2.6.35 and in mainline with your patches
>>> ?
>> In FSL 2.6.35, there are some free space in the OOB;
>> while in mainline we use all the free space in the OOB.
> OK, let me understand this in more detail.
>
> How does the NAND page look when written by FSL 2.6.35 and how does the NAND
> page look when written by current mainline ? Can you please tell in detail?
>
[1] for FSL 2.6.35, see gpmi_nfc_set_geometry():
     The ecc_strength is set at a fix value, such as:
           "set ecc_strength with 8 for page size 2048";

     Why set the ecc_strength with 8? just based on the experiences, not 
based on the
     chip's datasheets.

     So we can have some spare space in the OOB, after we setting the 
BCH with the ecc_strength.

[2] for mainline, see common_nfc_set_geometry():
     Please see the diagrams in the set_geometry_by_ecc_info() and 
legacy_set_geometry().


     If we CAN use the ecc info from the chip's datasheet, just like in 
FSL_2.6.35, we may
     have some spare space in the OOB; else we use all the OOB.



>>> Is there any way to mount JFFS2 written with FSL 2.6.35 on current
>>> mainline? Thus far, neither me nor Hector were able to mount such
>>> partition with the same result.
>> The gpmi driver in FSL 2.6.35 is different from the mainline.
> I was under the impression the mainline driver is an evolution of the FSL 2.6.35
> driver. Is this assumption incorrect?
>
yes.
>> The two drivers are not compatible to each other.
> OK, like I said, if we cannot produce a drop-in replacement of old FSL 2.6.35
> kernel, this is a problem. People will come and they will be running into this
> issue. Thus, let us focus on producing a compatible JFFS2 patch.
I do not think it is a problem. The FSL 2.6.35 does not support the JFFS2.


thanks
Huang Shijie