AM623: about gpmc nand flash driver

Hi Bin

  I know the  BBT management method,   but we don’t want to create  a flash based BBT, only want to create a memory BBT. 

 but from the TI GPMC nand driver code omap2.c.  if not set  NAND_BBT_USE_FLASH flag, will set NAND_SKIP_BBTSCAN .  so  If not  to create a flash based BBT,  also not to create a memory BBT.      please help check the reason.  

Hi Bert,

Now I understood your question. Let me know look into it and get back to you.

HI Bin

  do you think it have any issues  If I  delete the NAND_SKIP_BBTSCAN  flag ?

Hi Bert,

I don't know, the omap2 nand driver never used BBT logic, it is not validated.

Hi Bin 

It seems ok when delete NAND_SKIP_BBTSCAN flag. the system can boot ok and application can work normally.  

 Do you know what test cases I can do to ensure reliability base on your experience ？

Hi Bert,

It has not been validated, so I won't be able to tell its reliability.

Why do you want to remove this flag to use in-memory BBT management?

hi Bin

   The root cause is TI uboot and TI linux  default  flash based BBT   is not same .

As said before,  in linux drivers/mtd/nand/raw/omap2.c,  if set NAND_BBT_USE_FLASH, will also set NAND_BBT_NO_OOB . but in uboot code  drivers/mtd/nand/raw/omap_gpmc.c not set it .  so in order to keep the same BBT between uboot and linux, We should change code in linux or uboot.  

please check

Hi Bert,

Bert said:

As said before,  in linux drivers/mtd/nand/raw/omap2.c,  if set NAND_BBT_USE_FLASH, will also set NAND_BBT_NO_OOB .

NAND_BBT_USE_FLASH in kernel is never set in omap2.c,

  2244         if (info->flash_bbt)                                                    
     1                 nand_chip->bbt_options |= NAND_BBT_USE_FLASH;

since info->flash_bbt flag is never set.

So the behavior in kernel driver is the same as that in U-Boot. Did I miss anything?

Hi Bin

omap_nand_attach_chip--->

    {     if (chip->bbt_options & NAND_BBT_USE_FLASH)
              chip->bbt_options |= NAND_BBT_NO_OOB;
         else
          chip->options |= NAND_SKIP_BBTSCAN;

}

above code in linux drivers/mtd/nand/raw/omap2.c done what I said ： if set NAND_BBT_USE_FLASH, will also set NAND_BBT_NO_OOB .

uboot and linux both set NAND_BBT_USE_FLASH flag through device tree  nand-on-flash-bbt property

if (of_property_read_bool(dn, "nand-on-flash-bbt"))
chip->bbt_options |= NAND_BBT_USE_FLASH;

Hi Bert,

Now I understand your concerns. I am checking on this internally and will get back to you once I have update.

Hi Bert,

Since "nand-on-flash-bbt" DT properly has never been enabled in the SDK, it is not validated, I don't get a certain answer from internal discussion about its impact.

But by reviewing the code, since U-Boot and kernel uses the NAND_BBT_NO_OOB flag differently, there is a potential problem that the OOB could be corrupted if "nand-on-flash-bbt" was set in both U-Boot and kernel devicetree.