Re: [PATCH RFC] Alphascale ASM9260 NAND controller driver

[Boris Brezillon <boris.brezillon@free-electrons.com>]

On Wed, 17 Dec 2014 15:36:49 +0100
Oleksij Rempel <linux@rempel-privat.de> wrote:

> Am 17.12.2014 um 14:24 schrieb Boris Brezillon:
> > Hi Oleksij,
> > 
> > On Wed, 17 Dec 2014 12:45:17 +0100
> > Oleksij Rempel <linux@rempel-privat.de> wrote:
> > 
> >> I collected some questions with this driver. It will be great if you
> >> can help me:
> >> * Do HW_ECC driver should provideo option for SW_ECC?
> > 
> > This is not mandatory. I did it in the sunxi driver for testing
> > purpose, but it should work fine without it.
> > 
> >> * My HW do ECC correction for n-bits per 512B, it mean it will
> >> split block in 512B parts. If one of part has uncorrectable error, complete block will be
> >> reported as failed. Are there any way for partial recovery?
> > 
> > I think what you're calling block here is actually a page.
> > Regarding your question, there is no way to recover part of a page, but
> > each ECC block should be tested and max_bitflip should be returned
> > (even if some ECC blocks contains too many errors to be corrected).
> > Take a look at [1] for an example.
> 
> From Flash point of view block or part which i mean != page. In my case
> it is TOSHIBA TC58NVG0S3ETA00, organized as (2048 + 64) bytes × 64 pages
> × 1024blocks. The NFC will split each each 2048B page to 512B
> blocks/???/parts/sub_page/ecc_step/better_name.

Okay, so let's call it ECC step or ECC block, not just block, cause a
NAND block is containing several NAND pages.

> 
> HW_ECC provide bit_flip counter for each sub_page. If all sub_pages are
> recovered, there is no problem. Beside the question, how many bit should
> be counted. Right now max_bitflips = sum(all_sub_pages).


Then you should change it to return
max(nbitflips_on_chunk1, nbitflips_on_chunk2, ...)

> 
> Second problem which i have is that, there is only one ecc_error flag
> for all sub_pages. If one sub_page filed, i don't know which one. Ecc
> erroc counter register can't help here. Only way is to reread complete
> page with SW_ECC.

Then I don't have any solution right now (I'll think about it)...

> 
> >> * This HW reports count of ECC bitflips for each part. Do i need to return count of errors on
> >> all parts for one block?
> > 
> > Again: block == page, and no, you should only return the maximum
> > corrected bitflips (same example [1]).
> > 
> > 
> >> * If HW_ECC different stranges, how it should be configured? With DT or automatically
> >> calculated?
> > 
> > I don't get that one...
> > Are you talking about ECC requirements (ECC strength and steps) ?
> 
> Yes. Well, i can't choice ECC step(it is 512B on this HW), only strange.

You mean strength :-), then you should either use the values returned
by ONFI or the one defined in the strength_ds and step_ds fields.
DT porperties should override those definitions (for example to force
ECC strength based on a specific bootloader config).


-- 
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com