satip-axe/kernel/Documentation/mtd/stm-nand-afm-notes.txt
2015-03-26 17:24:57 +01:00

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STLinux NAND AFM driver - Release Notes
1. Overview
The stm-nand-afm driver adds support for the ST Microelectronics NAND AFM
Controller. The AFM Controller offers H/W assisted ECC, automated command
sequences, and a 128-byte data FIFO, all of which contribute to an improved
performance over the existing stm-nand-emi and stm-nand-flex drivers.
However, the AFM controller uses a different ECC layout to the default linux S/W
ECC layout (as used by the stm-nand-emi and stm-nand-flex drivers). Furthermore,
the AFM4 ECC layout may clash with the location of the factory-programmed
bad-block markers. As a result, a number of issues must be considered before
enabling the stm-nand-afm driver, particularly when migrating from the
stm-nand-flex or stm-nand-emi drivers.
2. ECC Schemes
The user needs to be aware of 3 ECC schemes:
* 3/256 ECC: 3 bytes of ECC per 256 bytes of data. This is the default linux
S/W ECC scheme and is used by the stm-nand-emi and stm-nand-flex drivers.
* boot-mode ECC: 3 bytes of ECC per 128 bytes of data (with an additional 1-byte
ID marker). This format is used by the NAND boot-controller. The layout of
the ECC bytes in OOB is such that it may clash with the location of
factory-programmed bad-block markers. Therefore, the use of FLASH-resident
bad block tables (BBTs) is advised to keep track of bad-blocks. Ideally, the
BBTs should be written to the device prior to writing any boot-mode data.
However, STLinux does now recognise boot-mode ECC data when scanning for
bad-blocks, so the creation of the FLASH-resident BBTs can be deferred to the
first boot if preferred, or avoided all-together. (Previously, STLinux would
typically interpret boot-mode ECC data as bad-block markers, and therefore
writing BBTs to FLASH prior to writing boot-mode data was mandatory.)
* AFM4 ECC: 4 bytes of ECC per 512 bytes of data (with an additional 3-byte ID
marker). This format is used by the stm-nand-afm driver (and is the only
scheme recognised by the PBL (Primary Boot Loader)). As with boot-mode ECC,
the layout in OOB is such that it may clash with the location of
factory-programmed bad-block markers. The same advice as before applies: the
use of FLASH-resident BBTs is recommended, although STLinux will recognise
correctly AFM4 data if required to perform the bad-block scan itself.
3. Migrating from stm-nand-flex or stm-nand-emi drivers
If the NAND device has been used previously with the stm-nand-emi or
stm-nand-flex driver, then it will need to be wiped before enabling the
stm-nand-afm driver. This includes erasing data blocks and any FLASH-resident
BBTs that may be present. However, care must be taken not to erase any
factory-programed bad-block markers since it may not be possible to recover this
information from the NAND device if the block is erased.
3.1 Erasing data blocks
This can be achieved using the flash_eraseall command on the NAND device's MTD
partitions. flash_eraseall is safe to use here since it will not attempt to
erase any blocks that are marked bad (this is true even if the debugfs attribute
"nanderasebb" has been set).
For example:
root@jim:~# cat /proc/mtd
dev: size erasesize name
mtd0: 00400000 00020000 "My NOR Root"
mtd1: 07c00000 00020000 "My NOR Home"
mtd2: 00800000 00020000 "NAND root"
mtd3: 3f800000 00020000 "NAND home"
root@jim:~# flash_eraseall /dev/mtd2
Skipping bad block at 0x00000000
Skipping bad block at 0x00020000
Erasing 128 Kibyte @ 40000 -- 3 % complete.
Skipping bad block at 0x00060000
Erasing 128 Kibyte @ a0000 -- 7 % complete.
Skipping bad block at 0x000c0000
Erasing 128 Kibyte @ 7e0000 -- 98 % complete.
root@jim:~# flash_eraseall /dev/mtd2
Skipping bad block at 0x00000000
Skipping bad block at 0x00020000
Erasing 128 Kibyte @ 40000 -- 3 % complete.
Skipping bad block at 0x00060000
Erasing 128 Kibyte @ a0000 -- 7 % complete.
Skipping bad block at 0x000c0000
Erasing 128 Kibyte @ 7e0000 -- 98 % complete.
root@jim:~# flash_eraseall /dev/mtd3
Erasing 128 Kibyte @ 115c0000 -- 27 % complete.
Skipping bad block at 0x115e0000
Erasing 128 Kibyte @ 2e140000 -- 72 % complete.
Skipping bad block at 0x2e160000
Erasing 128 Kibyte @ 36380000 -- 85 % complete.
Skipping bad block at 0x363a0000
Erasing 128 Kibyte @ 3f7e0000 -- 99 % complete.
3.2 Erasing FLASH-resident BBTs
If FLASH-resident BBTs have been used in the past, then these will need to be
erased manually. linux protects the area reserved for FLASH-resident BBTs
(typically the last 4 blocks of the NAND device) by presenting them as
bad-blocks to user applications. In order to erase the BBTs:
1) Enable the erasing of blocks that are marked as bad, via the debugfs
attribute "nanderasebb" (requires CONFIG_DEBUG_FS):
root@jim:~# echo 1 > /debug/nanderasebb
2) Use flash_erase on the blocks reserved for BBTs. For example:
root@jim:~# cat /proc/mtd
dev: size erasesize name
mtd0: 00400000 00020000 "My NOR Root"
mtd1: 07c00000 00020000 "My NOR Home"
mtd2: 00800000 00020000 "NAND root"
mtd3: 3f800000 00020000 "NAND home"
root@jim:~# flash_erase /dev/mtd3 0x3f780000 4
Erase Total 4 Units
Performing Flash Erase of length 131072 at offset 0x3f7e0000 done
4 Configuring the stm-nand-afm driver
4.1 Board setup file
The board setup file uses a marco, STM_NAND_DEVICE, to fill-in the NAND platform
data. The first argument is the driver binding which should be changed to
"stm-nand-afm". It is also recommended to add "NAND_USE_FLASH_BBT" to the chip
options bit-field (the last argument), if not already present.
4.2 Kconfig options
* MTD_NAND_STM_AFM: Enable the stm-nand-afm driver.
* STM_NAND_AFM_CACHED: Perform page reads via a cache-line. This option reduces
the impact of STBus latencies at the expense of an increased IRQ latency.
* STM_NAND_AFM_BOOTMODESUPPORT: Enable support for boot-mode ECC data (reading,
writing, and scanning bad-blocks). Support for boot-mode ECC is tied to a
specified MTD partition name (see below).
* STM_NAND_AFM_BOOTPARTITION: The name of the NAND boot partition. This can be
overridden on the kernel command line, using "nbootpart=<mtd_name>". By
default, boot-mode ECC is assumed to apply to the entire boot-partition.
* STM_NAND_AFM_PBLBOOTBOUNDARY: Select this option if using the PBL as the
boot-loader. The PBL boot-image contains both boot-mode ECC data and AFM4-ECC
data. The boundary between ECC schemes is embedded in the PBL image itself.
This option attempts to extract the boot-boundary from the PBL image, and
updates the extent to which boot-mode ECC applies within the boot-partition.