xref: /linux/Documentation/ABI/testing/sysfs-class-mtd (revision edbc4540e02c201bdd4f4d498ebb6ed517fd36e2)

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().  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 mtd_read().
		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.