Documentation/ABI/testing/sysfs-class-mtd

   1 What:           /sys/class/mtd/
   2 Date:           April 2009
   3 KernelVersion:  2.6.29
   4 Contact:        linux-mtd@lists.infradead.org
   5 Description:
   6                 The mtd/ class subdirectory belongs to the MTD subsystem
   7                 (MTD core).
   8
   9 What:           /sys/class/mtd/mtdX/
  10 Date:           April 2009
  11 KernelVersion:  2.6.29
  12 Contact:        linux-mtd@lists.infradead.org
  13 Description:
  14                 The /sys/class/mtd/mtd{0,1,2,3,...} directories correspond
  15                 to each /dev/mtdX character device.  These may represent
  16                 physical/simulated flash devices, partitions on a flash
  17                 device, or concatenated flash devices.
  18
  19 What:           /sys/class/mtd/mtdXro/
  20 Date:           April 2009
  21 KernelVersion:  2.6.29
  22 Contact:        linux-mtd@lists.infradead.org
  23 Description:
  24                 These directories provide the corresponding read-only device
  25                 nodes for /sys/class/mtd/mtdX/ .
  26
  27 What:           /sys/class/mtd/mtdX/dev
  28 Date:           April 2009
  29 KernelVersion:  2.6.29
  30 Contact:        linux-mtd@lists.infradead.org
  31 Description:
  32                 Major and minor numbers of the character device corresponding
  33                 to this MTD device (in <major>:<minor> format).  This is the
  34                 read-write device so <minor> will be even.
  35
  36 What:           /sys/class/mtd/mtdXro/dev
  37 Date:           April 2009
  38 KernelVersion:  2.6.29
  39 Contact:        linux-mtd@lists.infradead.org
  40 Description:
  41                 Major and minor numbers of the character device corresponding
  42                 to the read-only variant of thie MTD device (in
  43                 <major>:<minor> format).  In this case <minor> will be odd.
  44
  45 What:           /sys/class/mtd/mtdX/erasesize
  46 Date:           April 2009
  47 KernelVersion:  2.6.29
  48 Contact:        linux-mtd@lists.infradead.org
  49 Description:
  50                 "Major" erase size for the device.  If numeraseregions is
  51                 zero, this is the eraseblock size for the entire device.
  52                 Otherwise, the MEMGETREGIONCOUNT/MEMGETREGIONINFO ioctls
  53                 can be used to determine the actual eraseblock layout.
  54
  55 What:           /sys/class/mtd/mtdX/flags
  56 Date:           April 2009
  57 KernelVersion:  2.6.29
  58 Contact:        linux-mtd@lists.infradead.org
  59 Description:
  60                 A hexadecimal value representing the device flags, ORed
  61                 together:
  62
  63                 0x0400: MTD_WRITEABLE - device is writable
  64                 0x0800: MTD_BIT_WRITEABLE - single bits can be flipped
  65                 0x1000: MTD_NO_ERASE - no erase necessary
  66                 0x2000: MTD_POWERUP_LOCK - always locked after reset
  67
  68 What:           /sys/class/mtd/mtdX/name
  69 Date:           April 2009
  70 KernelVersion:  2.6.29
  71 Contact:        linux-mtd@lists.infradead.org
  72 Description:
  73                 A human-readable ASCII name for the device or partition.
  74                 This will match the name in /proc/mtd .
  75
  76 What:           /sys/class/mtd/mtdX/numeraseregions
  77 Date:           April 2009
  78 KernelVersion:  2.6.29
  79 Contact:        linux-mtd@lists.infradead.org
  80 Description:
  81                 For devices that have variable eraseblock sizes, this
  82                 provides the total number of erase regions.  Otherwise,
  83                 it will read back as zero.
  84
  85 What:           /sys/class/mtd/mtdX/oobsize
  86 Date:           April 2009
  87 KernelVersion:  2.6.29
  88 Contact:        linux-mtd@lists.infradead.org
  89 Description:
  90                 Number of OOB bytes per page.
  91
  92 What:           /sys/class/mtd/mtdX/size
  93 Date:           April 2009
  94 KernelVersion:  2.6.29
  95 Contact:        linux-mtd@lists.infradead.org
  96 Description:
  97                 Total size of the device/partition, in bytes.
  98
  99 What:           /sys/class/mtd/mtdX/type
 100 Date:           April 2009
 101 KernelVersion:  2.6.29
 102 Contact:        linux-mtd@lists.infradead.org
 103 Description:
 104                 One of the following ASCII strings, representing the device
 105                 type:
 106
 107                 absent, ram, rom, nor, nand, dataflash, ubi, unknown
 108
 109 What:           /sys/class/mtd/mtdX/writesize
 110 Date:           April 2009
 111 KernelVersion:  2.6.29
 112 Contact:        linux-mtd@lists.infradead.org
 113 Description:
 114                 Minimal writable flash unit size.  This will always be
 115                 a positive integer.
 116
 117                 In the case of NOR flash it is 1 (even though individual
 118                 bits can be cleared).
 119
 120                 In the case of NAND flash it is one NAND page (or a
 121                 half page, or a quarter page).
 122
 123                 In the case of ECC NOR, it is the ECC block size.
 124
 125 What:           /sys/class/mtd/mtdX/ecc_strength
 126 Date:           April 2012
 127 KernelVersion:  3.4
 128 Contact:        linux-mtd@lists.infradead.org
 129 Description:
 130                 Maximum number of bit errors that the device is capable of
 131                 correcting within each region covering an ecc step.  This will
 132                 always be a non-negative integer.  Note that some devices will
 133                 have multiple ecc steps within each writesize region.
 134
 135                 In the case of devices lacking any ECC capability, it is 0.
 136
 137 What:           /sys/class/mtd/mtdX/bitflip_threshold
 138 Date:           April 2012
 139 KernelVersion:  3.4
 140 Contact:        linux-mtd@lists.infradead.org
 141 Description:
 142                 This allows the user to examine and adjust the criteria by which
 143                 mtd returns -EUCLEAN from mtd_read() and mtd_read_oob().  If the
 144                 maximum number of bit errors that were corrected on any single
 145                 region comprising an ecc step (as reported by the driver) equals
 146                 or exceeds this value, -EUCLEAN is returned.  Otherwise, absent
 147                 an error, 0 is returned.  Higher layers (e.g., UBI) use this
 148                 return code as an indication that an erase block may be
 149                 degrading and should be scrutinized as a candidate for being
 150                 marked as bad.
 151
 152                 The initial value may be specified by the flash device driver.
 153                 If not, then the default value is ecc_strength.
 154
 155                 The introduction of this feature brings a subtle change to the
 156                 meaning of the -EUCLEAN return code.  Previously, it was
 157                 interpreted to mean simply "one or more bit errors were
 158                 corrected".  Its new interpretation can be phrased as "a
 159                 dangerously high number of bit errors were corrected on one or
 160                 more regions comprising an ecc step".  The precise definition of
 161                 "dangerously high" can be adjusted by the user with
 162                 bitflip_threshold.  Users are discouraged from doing this,
 163                 however, unless they know what they are doing and have intimate
 164                 knowledge of the properties of their device.  Broadly speaking,
 165                 bitflip_threshold should be low enough to detect genuine erase
 166                 block degradation, but high enough to avoid the consequences of
 167                 a persistent return value of -EUCLEAN on devices where sticky
 168                 bitflips occur.  Note that if bitflip_threshold exceeds
 169                 ecc_strength, -EUCLEAN is never returned by the read operations.
 170                 Conversely, if bitflip_threshold is zero, -EUCLEAN is always
 171                 returned, absent a hard error.
 172
 173                 This is generally applicable only to NAND flash devices with ECC
 174                 capability.  It is ignored on devices lacking ECC capability;
 175                 i.e., devices for which ecc_strength is zero.