LXR uboot/doc/README.fuse

   1Fuse API functions and commands
   2
   3The fuse API allows to control a fusebox and how it is used by the upper
   4hardware layers.
   5
   6A fuse corresponds to a single non-volatile memory bit that can be programmed
   7(i.e. blown, set to 1) only once. The programming operation is irreversible. A
   8fuse that has not been programmed reads 0.
   9
  10Fuses can be used by SoCs to store various permanent configuration and data,
  11e.g. boot configuration, security configuration, MAC addresses, etc.
  12
  13A fuse word is the smallest group of fuses that can be read at once from the
  14fusebox control IP registers. This is limited to 32 bits with the current API.
  15
  16A fuse bank is the smallest group of fuse words having a common ID, as defined
  17by each SoC.
  18
  19Upon startup, the fusebox control IP reads the fuse values and stores them to a
  20volatile shadow cache.
  21
  22See the README files of the drivers implementing this API in order to know the
  23SoC- and implementation-specific details.
  24
  25Functions / commands:
  26
  27   int fuse_read(u32 bank, u32 word, u32 *val);
  28   fuse read <bank> <word> [<cnt>]
  29      Read fuse words from the shadow cache.
  30
  31   int fuse_sense(u32 bank, u32 word, u32 *val);
  32   fuse sense <bank> <word> [<cnt>]
  33      Sense - i.e. read directly from the fusebox, skipping the shadow cache -
  34      fuse words. This operation does not update the shadow cache.
  35
  36      This is useful to know the true value of fuses if an override has been
  37      performed (see below).
  38
  39   int fuse_prog(u32 bank, u32 word, u32 val);
  40   fuse prog [-y] <bank> <word> <hexval> [<hexval>...]
  41      Program fuse words. This operation directly affects the fusebox and is
  42      irreversible. The shadow cache is updated accordingly or not, depending on
  43      each IP.
  44
  45      Only the bits to be programmed should be set in the input value (i.e. for
  46      fuse bits that have already been programmed and hence should be left
  47      unchanged by a further programming, it is preferable to clear the
  48      corresponding bits in the input value in order not to perform a new
  49      hardware programming operation on these fuse bits).
  50
  51   int fuse_override(u32 bank, u32 word, u32 val);
  52   fuse override <bank> <word> <hexval> [<hexval>...]
  53      Override fuse words in the shadow cache.
  54
  55      The fusebox is unaffected, so following this operation, the shadow cache
  56      may differ from the fusebox values. Read or sense operations can then be
  57      used to get the values from the shadow cache or from the fusebox.
  58
  59      This is useful to change the behaviors linked to some cached fuse values,
  60      either because this is needed only temporarily, or because some of the
  61      fuses have already been programmed or are locked (if the SoC allows to
  62      override a locked fuse).
  63
  64Configuration:
  65
  66   CONFIG_CMD_FUSE
  67      Define this to enable the fuse commands.
  68