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@@ -0,0 +1,66 @@
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.. SPDX-License-Identifier: GPL-2.0+
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Events
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======
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U-Boot supports a way for various events to be handled by interested
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subsystems. This provide a generic way to handle 'hooks' like setting up the
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CPUs after driver model is active, or reading a partition table after a new
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block device is probed.
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Rather than using weak functions and direct calls across subsystemss, it is
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often easier to use an event.
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An event consists of a type (e.g. EVT_DM_POST_INIT) and some optional data,
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in `union event_data`. An event spy can be creasted to watch for events of a
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particular type. When the event is created, it is sent to each spy in turn.
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Declaring a spy
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---------------
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To declare a spy, use something like this::
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static int snow_setup_cpus(void *ctx, struct event *event)
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{
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/* do something */
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return 0;
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}
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EVENT_SPY(EVT_DM_POST_INIT, snow_setup_cpus);
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Your function is called when EVT_DM_POST_INIT is emitted, i.e. after driver
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model is inited (in SPL, or in U-Boot proper before and after relocation).
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Debugging
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---------
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To assist with debugging events, enable `CONFIG_EVENT_DEBUG` and
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`CONFIG_CMD_EVENT`. The :doc:`../usage/cmd/event` command can then be used to
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provide a spy list.
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It is also possible to list spy information from the U-Boot executable,, using
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the `event_dump.py` script::
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$ scripts/event_dump.py /tmp/b/sandbox/u-boot
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Event type Id Source location
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-------------------- ------------------------------ ------------------------------
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EVT_MISC_INIT_F f:sandbox_misc_init_f arch/sandbox/cpu/start.c:125
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This shows each event spy in U-Boot, along with the event type, function name
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(or ID) and source location.
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Note that if `CONFIG_EVENT_DEBUG` is not enabled, the event ID is missing, so
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the function is shown instead (with an `f:` prefix as above). Since the ID is
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generally the same as the function name, this does not matter much.
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The event type is decoded by the symbol used by U-Boot for the event linker
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list. Symbols have the form::
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_u_boot_list_2_evspy_info_2_EVT_MISC_INIT_F
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so the event type can be read from the end. To manually list spy information
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in an image, use $(CROSS_COMPILE)nm::
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nm u-boot |grep evspy |grep list
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00000000002d6300 D _u_boot_list_2_evspy_info_2_EVT_MISC_INIT_F
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Tom Rini