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