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What: /sys/class/mtd/
Date: April 2009
KernelVersion: 2.6.29
Contact: linux-mtd@lists.infradead.org
Description:
The mtd/ class subdirectory belongs to the MTD subsystem
(MTD core).
What: /sys/class/mtd/mtdX/
Date: April 2009
KernelVersion: 2.6.29
Contact: linux-mtd@lists.infradead.org
Description:
The /sys/class/mtd/mtd{0,1,2,3,...} directories correspond
to each /dev/mtdX character device. These may represent
physical/simulated flash devices, partitions on a flash
device, or concatenated flash devices. They exist regardless
of whether CONFIG_MTD_CHAR is actually enabled.
What: /sys/class/mtd/mtdXro/
Date: April 2009
KernelVersion: 2.6.29
Contact: linux-mtd@lists.infradead.org
Description:
These directories provide the corresponding read-only device
nodes for /sys/class/mtd/mtdX/ . They are only created
(for the benefit of udev) if CONFIG_MTD_CHAR is enabled.
What: /sys/class/mtd/mtdX/dev
Date: April 2009
KernelVersion: 2.6.29
Contact: linux-mtd@lists.infradead.org
Description:
Major and minor numbers of the character device corresponding
to this MTD device (in <major>:<minor> format). This is the
read-write device so <minor> will be even.
What: /sys/class/mtd/mtdXro/dev
Date: April 2009
KernelVersion: 2.6.29
Contact: linux-mtd@lists.infradead.org
Description:
Major and minor numbers of the character device corresponding
to the read-only variant of thie MTD device (in
<major>:<minor> format). In this case <minor> will be odd.
What: /sys/class/mtd/mtdX/erasesize
Date: April 2009
KernelVersion: 2.6.29
Contact: linux-mtd@lists.infradead.org
Description:
"Major" erase size for the device. If numeraseregions is
zero, this is the eraseblock size for the entire device.
Otherwise, the MEMGETREGIONCOUNT/MEMGETREGIONINFO ioctls
can be used to determine the actual eraseblock layout.
What: /sys/class/mtd/mtdX/flags
Date: April 2009
KernelVersion: 2.6.29
Contact: linux-mtd@lists.infradead.org
Description:
A hexadecimal value representing the device flags, ORed
together:
0x0400: MTD_WRITEABLE - device is writable
0x0800: MTD_BIT_WRITEABLE - single bits can be flipped
0x1000: MTD_NO_ERASE - no erase necessary
0x2000: MTD_POWERUP_LOCK - always locked after reset
What: /sys/class/mtd/mtdX/name
Date: April 2009
KernelVersion: 2.6.29
Contact: linux-mtd@lists.infradead.org
Description:
A human-readable ASCII name for the device or partition.
This will match the name in /proc/mtd .
What: /sys/class/mtd/mtdX/numeraseregions
Date: April 2009
KernelVersion: 2.6.29
Contact: linux-mtd@lists.infradead.org
Description:
For devices that have variable eraseblock sizes, this
provides the total number of erase regions. Otherwise,
it will read back as zero.
What: /sys/class/mtd/mtdX/oobsize
Date: April 2009
KernelVersion: 2.6.29
Contact: linux-mtd@lists.infradead.org
Description:
Number of OOB bytes per page.
What: /sys/class/mtd/mtdX/size
Date: April 2009
KernelVersion: 2.6.29
Contact: linux-mtd@lists.infradead.org
Description:
Total size of the device/partition, in bytes.
What: /sys/class/mtd/mtdX/type
Date: April 2009
KernelVersion: 2.6.29
Contact: linux-mtd@lists.infradead.org
Description:
One of the following ASCII strings, representing the device
type:
absent, ram, rom, nor, nand, dataflash, ubi, unknown
What: /sys/class/mtd/mtdX/writesize
Date: April 2009
KernelVersion: 2.6.29
Contact: linux-mtd@lists.infradead.org
Description:
Minimal writable flash unit size. This will always be
a positive integer.
In the case of NOR flash it is 1 (even though individual
bits can be cleared).
In the case of NAND flash it is one NAND page (or a
half page, or a quarter page).
In the case of ECC NOR, it is the ECC block size.
What: /sys/class/mtd/mtdX/ecc_strength
Date: April 2012
KernelVersion: 3.4
Contact: linux-mtd@lists.infradead.org
Description:
Maximum number of bit errors that the device is capable of
correcting within each region covering an ecc step. This will
always be a non-negative integer. Note that some devices will
have multiple ecc steps within each writesize region.
In the case of devices lacking any ECC capability, it is 0.
What: /sys/class/mtd/mtdX/bitflip_threshold
Date: April 2012
KernelVersion: 3.4
Contact: linux-mtd@lists.infradead.org
Description:
This allows the user to examine and adjust the criteria by which
mtd returns -EUCLEAN from mtd_read() and mtd_read_oob(). If the
maximum number of bit errors that were corrected on any single
region comprising an ecc step (as reported by the driver) equals
or exceeds this value, -EUCLEAN is returned. Otherwise, absent
an error, 0 is returned. Higher layers (e.g., UBI) use this
return code as an indication that an erase block may be
degrading and should be scrutinized as a candidate for being
marked as bad.
The initial value may be specified by the flash device driver.
If not, then the default value is ecc_strength.
The introduction of this feature brings a subtle change to the
meaning of the -EUCLEAN return code. Previously, it was
interpreted to mean simply "one or more bit errors were
corrected". Its new interpretation can be phrased as "a
dangerously high number of bit errors were corrected on one or
more regions comprising an ecc step". The precise definition of
"dangerously high" can be adjusted by the user with
bitflip_threshold. Users are discouraged from doing this,
however, unless they know what they are doing and have intimate
knowledge of the properties of their device. Broadly speaking,
bitflip_threshold should be low enough to detect genuine erase
block degradation, but high enough to avoid the consequences of
a persistent return value of -EUCLEAN on devices where sticky
bitflips occur. Note that if bitflip_threshold exceeds
ecc_strength, -EUCLEAN is never returned by the read operations.
Conversely, if bitflip_threshold is zero, -EUCLEAN is always
returned, absent a hard error.
This is generally applicable only to NAND flash devices with ECC
capability. It is ignored on devices lacking ECC capability;
i.e., devices for which ecc_strength is zero.
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