Initialising NAND OOB with Software ECC

[tglx@linutronix.de (Thomas Gleixner)]

On Friday 14 February 2003 10:46, Phil Thompson wrote:
> How do you want it implemented?
> Just a new ioctl that sets the selector for subsequent MEMWRITEDATA and
> MEMREADDATA calls?
Not a good idea.

> IMHO it would be cleaner to replace the struct mtd_oob_buf argument to
> MEMWRITEDATA and MEMREADDATA with a structure that included the selector to
> use for that operation. But that would break binary compatibility. Is this
> an option at this stage?
Yep, as it's for NAND only and as there are no tools, which are usefull, I 
think we can do this and implement it in a clean way. Then we can overhaul 
nandtest utils in mtd/utils to give an example. This should include a 
"copyImageToNAND" utility with support for other filesystems too.

My suggestion:

struct nand_ctrl {
	int	oob_select;	// selector for OOB usage
	int	data_lenght;	// length of data
	int	oob_length;	// length of oob-buffer
};
oob_length can be 0. If its not zero it must be 8 * (data_length / 256) for 
write and 12 * (data_length / 256) for read, as nand_read_ecc appends the 
ecc_status result behind each 8 byte OOB.
struct nand_oob_read {
	char	oob_data[8];
	int	ecc_status;
}

JFFS2 needs no oob buffer for write, but YAFFS does.

data_length for write should be checked, if it is a multiple of page size 
(mtd->oobblock), which is either 256 or 512 at the moment. Deny writing parts 
of pages.

David: any complaints ?

-- 
Thomas
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