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Add documentation for the 'fuse' sub-system commands in doc/usage/cmd/fuse.rst file. Remove doc/README.fuse file. Signed-off-by: Harsha Vardhan V M <h-vm@ti.com>
156 lines
4.2 KiB
ReStructuredText
156 lines
4.2 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0+
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.. index::
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single: fuse (command)
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fuse command
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============
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Synopsis
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--------
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::
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fuse read <bank> <word> [<cnt>]
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fuse cmp <bank> <word> <hexval>
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fuse readm <bank> <word> <addr> [<cnt>]
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fuse sense <bank> <word> [<cnt>]
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fuse prog [-y] <bank> <word> <hexval> [<hexval>...]
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fuse override <bank> <word> <hexval> [<hexval>...]
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Description
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-----------
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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.
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A fuse that has not been programmed reads as 0.
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Fuses can be used by SoCs to store various permanent configurations and data,
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such as boot configurations, security settings, MAC addresses, etc.
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A fuse 'word' is the smallest group of fuses that can be read at once from
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the fusebox control IP registers. In the current API, this is limited to 32 bits.
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A fuse 'bank' is the smallest group of fuse words having a common ID, as
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defined by each SoC.
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Upon startup, the fusebox control IP reads the fuse values and stores them in a
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volatile shadow cache.
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Commands
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--------
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- **fuse read <bank> <word> [<cnt>]**
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Reads 1 or 'cnt' fuse words, starting at 'word' from the shadow cache.
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- **fuse cmp <bank> <word> <hexval>**
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Compares 'hexval' to fuse at 'word'.
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- **fuse readm <bank> <word> <addr> [<cnt>]**
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Reads 1 or 'cnt' fuse words, starting at 'word' into memory at 'addr'.
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- **fuse sense <bank> <word> [<cnt>]**
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Sense 1 or 'cnt' fuse words, starting at 'word'.
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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. This is
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useful to know the true value of fuses if an override has been
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performed (see below).
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- **fuse prog [-y] <bank> <word> <hexval> [<hexval>...]**
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Permanently programs 1 or several fuse words, starting at 'word'.
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This operation directly affects the fusebox and is irreversible. The
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shadow cache is updated accordingly or not, depending on each IP.
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Only the bits to be programmed should be set in the input value (i.e.
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for fuse bits that have already been programmed and hence should be
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left unchanged by a further programming, it is preferable to clear
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the corresponding bits in the input value in order not to perform a
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new hardware programming operation on these fuse bits).
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- **fuse override <bank> <word> <hexval> [<hexval>...]**
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Override 1 or several fuse words, starting at 'word' 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 behaviours 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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Examples
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--------
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fuse read
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~~~~~~~~~
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::
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u-boot=> fuse read 0 1
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Reading bank 0:
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Word 0x00000001: 00000001
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fuse cmp
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~~~~~~~~
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::
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u-boot=> fuse cmp 0 1 0x1
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Comparing bank 0:
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Word 0x00000001:
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Value 0x00000001:0x00000001
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passed
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fuse readm
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~~~~~~~~~~
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::
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u-boot=> fuse readm 0 1 0x83000000
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Reading bank 0 len 1 to 0x83000000
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fuse sense
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~~~~~~~~~~
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::
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u-boot=> fuse sense 0 1
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Sensing bank 0:
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Word 0x00000001: 00000001
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fuse prog
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~~~~~~~~~
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::
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u-boot=> fuse prog 0 1 0x00000002
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Programming bank 0 word 0x00000001 to 0x00000002...
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Warning: Programming fuses is an irreversible operation!
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This may brick your system.
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Use this command only if you are sure of what you are doing!
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Really perform this fuse programming? <y/N>
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y
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fuse override
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~~~~~~~~~~~~~
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::
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u-boot=> fuse override 0 1 0x00000003
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Overriding bank 0 word 0x00000001 with 0x00000003...
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Configuration
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-------------
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The fuse commands are available if CONFIG_CMD_FUSE=y.
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Return code
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-----------
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The return value $? is set to 0 (true) if the command is successful,
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1 (false) otherwise.
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