The initial layout for such NAND chips was the following:
+----------------------------------------------------------------------------+
| 1024 (data) | 30 (ECC) | 1024 (data) | 30 (ECC) | 32 (free OOB) | 30 (ECC) |
+----------------------------------------------------------------------------+
This layout has a weakness: reading empty pages trigger ECC errors
(this is expected), but the hardware ECC engine tries to correct the
data anyway and creates itself bitflips, hence bitflips are detected
in erased pages while actually there are none in the NAND chip.
Two solutions have been found at the same time. One was to enlarge the
free OOB area to 64 bytes, changing the layout to be:
+----------------------------------------------------------------------------+
| 1024 (data) | 30 (ECC) | 1024 (data) | 30 (ECC) | 64 (free OOB) | 30 (ECC) |
+----------------------------------------------------------------------------+
^^
The very big drawbacks of this solution are:
1/ It prevents booting from NAND.
2/ The current Linux driver (marvell_nand) does not have such problem
because it already re-reads possible empty pages in raw mode before
checking for bitflips. Using different layouts in U-Boot and Linux
would simply not work.
As this driver does support raw reads now and uses it to check for
empty pages, let's forget about this broken hack and return to the
initial layout with only 32 free OOB bytes.
Fixes: ac56a3b30c ("mtd: nand: pxa3xx: add support for 2KB 8-bit flash")
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Acked-by: Jagan Teki <jagan@openedev.com>
This only applies on BCH path.
When an empty page is read, it triggers an uncorrectable error. While
this is expected, the ECC engine might produce itself bitflips in the
read data under certain layouts. To overcome this situation, always
re-read the entire page in raw mode and check for the whole page to be
empty.
Also report the right number of bitflips if there are any.
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Acked-by: Jagan Teki <jagan@openedev.com>
Raw read support is added by editing a few code sections:
->handle_data_pio() includes the ECC bytes that are not consumed
anymore by the ECC engine.
->prepare_set_command() is changed so that the ECC bytes are
requested as part of the data I/O length.
->drain_fifo() shall also avoid checking the R/B pin too often
when in raw mode.
->read_page_raw()/->read_oob_raw() are written from scratch.
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Acked-by: Jagan Teki <jagan@openedev.com>
NAND flavors, like serial and parallel, have a lot in common and would
benefit to share code. Let's move raw (parallel) NAND specific code in a
raw/ subdirectory, to ease the addition of a core file in nand/ and the
introduction of a spi/ subdirectory specific to SPI NANDs.
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
2018-09-20 20:10:49 +05:30
Renamed from drivers/mtd/nand/pxa3xx_nand.c (Browse further)
