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Review docs and header for board_fdt_fixup()

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Now that pre-relocation devicetree mnipulation uses an event rather than
a weak function, update the docs and remove the function from the init.h
header.

Series-to: u-boot
Cover-letter:
fdt: Use events for pre-relocation devicetree manipulation
At present a weak function is used to modify the devicetree before
relocation. This is not ideal, since it is hard to find out whether a
board provides this function or not.

Another issue is that the fixups happen in multiple places in the init
sequences, with a confusing set of #if checks.

A final issue is that the fixups are done on the flat tree, which can be
quite inefficient.

This series introduces a new event to handle these fixups, converts all
boards and update the docs. The event passes an oftree instead of a
void * so that in future it can support livetree updates.

It would be possible to remove OF_BOARD_FIXUP and just always send the
event, but this would have a small code-size impact on the majority of
boards, since only about 45 use this feature.
END
This commit is contained in:
Simon Glass
2025-06-05 06:10:10 -06:00
parent 160269a21c
commit e815adea77
3 changed files with 23 additions and 13 deletions
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31
doc/develop/driver-model/fdt-fixup.rst
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@@ -61,14 +61,27 @@ Implementation
--------------
To take advantage of the pre-relocation device tree manipulation mechanism,
boards have to implement the function board_fix_fdt, which has the following
signature:
boards have to implement a spy for the EVT_FT_FIXUP_F:
.. code-block:: c
int board_fix_fdt (void *rw_fdt_blob)
#include <event.h>
The passed-in void pointer is a writeable pointer to the device tree, which can
static int myboard_fix_fdt(void *ctx, struct event *event)
{
void *blob = oftree_lookup_fdt(event->data.ft_fixup_f.tree);
// Modify blob here
return 0;
}
EVENT_SPY_FULL(EVT_FT_FIXUP_F, myboard_fix_fdt);
For this to build successfuly, you will need to select or imply EVENT in
Kconfig. It may already be done for your board due to other features.
The event provides an oftree, converted to a writeable pointer to the device
tree, in the declaration of `blob` above. This pointer can
be used to manipulate the device tree using e.g. functions from
include/fdt_support.h. The return value should either be 0 in case of
successful execution of the device tree manipulation or something else for a
@@ -84,7 +97,7 @@ to be called::
+----------------------------------------------------------+
| WARNING: The actual manipulation of the device tree has |
| to be the _last_ set of operations in board_fix_fdt! |
| to be the _last_ set of operations in myboard_fix_fdt! |
| Since the pre-relocation driver model does not adapt to |
| changes made to the device tree either, its references |
| into the device tree will be invalid after manipulating |
@@ -97,7 +110,7 @@ following:
.. code-block:: c
int board_fix_fdt(void *rw_fdt_blob)
static int myboard_fix_fdt(void *ctx, struct event *event)
{
/*
* Collect information about device's hardware and store
@@ -118,7 +131,7 @@ Example
-------
The controlcenterdc board (board/gdsys/a38x/controlcenterdc.c) features a
board_fix_fdt function, in which six GPIO expanders (which might be present or
EVT_FT_FIXUP_F function, in which six GPIO expanders (which might be present or
not, since they are on daughter boards) on a I2C bus are queried for, and
subsequently deactivated in the device tree if they are not present.
@@ -128,5 +141,5 @@ it is safe to call it after the tree has already been manipulated.
Work to be done
---------------
* The application of device tree overlay should be possible in board_fixup_fdt,
but has not been tested at this stage.
* The application of device tree overlay should be possible in the fixup
function, but has not been tested at this stage.