Re: 2nd problem with read_subpage() ?

[Artem Bityutskiy <dedekind@infradead.org>]

On Tue, 2008-07-29 at 12:30 +0300, Artem Bityutskiy wrote:
> On Tue, 2008-07-29 at 09:53 +0300, Artem Bityutskiy wrote:
> > Glance at nand_do_read_ops():
> > 
> > 
> > if (likely(sndcmd)) {
> >         chip->cmdfunc(mtd, NAND_CMD_READ0, 0x00, page);
> >         sndcmd = 0;
> > }
> 
> Alexey,
> 
> my investigation showed that this "random output" command is not
> supported by all flashes. ST-micro NANDs seems to support it
> (I checked 2 manuals), while Sumsung NANDs do not (checked manual
> for K9XXG08UXA). This means your implementation will break many
> systems and should be either fixed or reverted.

I tried to implement this command in nandsim and test it with your
patch and found that there is something wring with how you use it.

What I do is dd if=/dev/mtd0 of=file bs=512 count=1 - just read one
sub-page. And in nandsim I see the following:

1. NAND_CMD_READ0 command, - read from eraseblock 0, column 0. This is
fine and seems to be called from nand_do_read_ops():

if (likely(sndcmd)) {
	chip->cmdfunc(mtd, NAND_CMD_READ0, 0x00, page);
        sndcmd = 0;
}

2. Then NAND_CMD_RNDREAD command is issued with column address
0x828, which is completely weird. It is called from nand_read_subpage():

...
if (eccpos[(start_step + num_steps) * chip->ecc.bytes] & (busw - 1))
	aligned_len++;

chip->cmdfunc(mtd, NAND_CMD_RNDOUT, mtd->writesize + aligned_pos, -1);
chip->read_buf(mtd, &chip->oob_poi[aligned_pos], aligned_len);
....

I do not understand what is going on.

-- 
Best regards,
Artem Bityutskiy (Битюцкий Артём)