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.. SPDX-License-Identifier: GPL-2.0+
Events
======
U-Boot supports a way for various events to be handled by interested
subsystems. This provide a generic way to handle 'hooks' like setting up the
CPUs after driver model is active, or reading a partition table after a new
block device is probed.
Rather than using weak functions and direct calls across subsystemss, it is
often easier to use an event.
An event consists of a type (e.g. EVT_DM_POST_INIT) and some optional data,
in `union event_data`. An event spy can be creasted to watch for events of a
particular type. When the event is created, it is sent to each spy in turn.
Declaring a spy
---------------
To declare a spy, use something like this::
static int snow_setup_cpus(void *ctx, struct event *event)
{
/* do something */
return 0;
}
EVENT_SPY(EVT_DM_POST_INIT, snow_setup_cpus);
Your function is called when EVT_DM_POST_INIT is emitted, i.e. after driver
model is inited (in SPL, or in U-Boot proper before and after relocation).
Debugging
---------
To assist with debugging events, enable `CONFIG_EVENT_DEBUG` and
`CONFIG_CMD_EVENT`. The :doc:`../usage/cmd/event` command can then be used to
provide a spy list.
It is also possible to list spy information from the U-Boot executable,, using
the `event_dump.py` script::
$ scripts/event_dump.py /tmp/b/sandbox/u-boot
Event type Id Source location
-------------------- ------------------------------ ------------------------------
EVT_MISC_INIT_F f:sandbox_misc_init_f arch/sandbox/cpu/start.c:125
This shows each event spy in U-Boot, along with the event type, function name
(or ID) and source location.
Note that if `CONFIG_EVENT_DEBUG` is not enabled, the event ID is missing, so
the function is shown instead (with an `f:` prefix as above). Since the ID is
generally the same as the function name, this does not matter much.
The event type is decoded by the symbol used by U-Boot for the event linker
list. Symbols have the form::
_u_boot_list_2_evspy_info_2_EVT_MISC_INIT_F
so the event type can be read from the end. To manually list spy information
in an image, use $(CROSS_COMPILE)nm::
nm u-boot |grep evspy |grep list
00000000002d6300 D _u_boot_list_2_evspy_info_2_EVT_MISC_INIT_F
|
