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- Fuse API functions and commands
- The fuse API allows to control a fusebox and how it is used by the upper
- hardware layers.
- A fuse corresponds to a single non-volatile memory bit that can be programmed
- (i.e. blown, set to 1) only once. The programming operation is irreversible. A
- fuse that has not been programmed reads 0.
- Fuses can be used by SoCs to store various permanent configuration and data,
- e.g. boot configuration, security configuration, MAC addresses, etc.
- A fuse word is the smallest group of fuses that can be read at once from the
- fusebox control IP registers. This is limited to 32 bits with the current API.
- A fuse bank is the smallest group of fuse words having a common ID, as defined
- by each SoC.
- Upon startup, the fusebox control IP reads the fuse values and stores them to a
- volatile shadow cache.
- See the README files of the drivers implementing this API in order to know the
- SoC- and implementation-specific details.
- Functions / commands:
- int fuse_read(u32 bank, u32 word, u32 *val);
- fuse read <bank> <word> [<cnt>]
- Read fuse words from the shadow cache.
- int fuse_sense(u32 bank, u32 word, u32 *val);
- fuse sense <bank> <word> [<cnt>]
- Sense - i.e. read directly from the fusebox, skipping the shadow cache -
- fuse words. This operation does not update the shadow cache.
- This is useful to know the true value of fuses if an override has been
- performed (see below).
- int fuse_prog(u32 bank, u32 word, u32 val);
- fuse prog [-y] <bank> <word> <hexval> [<hexval>...]
- Program fuse words. This operation directly affects the fusebox and is
- irreversible. The shadow cache is updated accordingly or not, depending on
- each IP.
- Only the bits to be programmed should be set in the input value (i.e. for
- fuse bits that have already been programmed and hence should be left
- unchanged by a further programming, it is preferable to clear the
- corresponding bits in the input value in order not to perform a new
- hardware programming operation on these fuse bits).
- int fuse_override(u32 bank, u32 word, u32 val);
- fuse override <bank> <word> <hexval> [<hexval>...]
- Override fuse words in the shadow cache.
- The fusebox is unaffected, so following this operation, the shadow cache
- may differ from the fusebox values. Read or sense operations can then be
- used to get the values from the shadow cache or from the fusebox.
- This is useful to change the behaviors linked to some cached fuse values,
- either because this is needed only temporarily, or because some of the
- fuses have already been programmed or are locked (if the SoC allows to
- override a locked fuse).
- Configuration:
- CONFIG_CMD_FUSE
- Define this to enable the fuse commands.
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