mirror of
https://github.com/AsahiLinux/u-boot
synced 2024-12-27 05:23:34 +00:00
68 lines
2.7 KiB
Text
68 lines
2.7 KiB
Text
|
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.
|