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