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There are of course not a whole lot of examples in-tree yet, but
before they appear, let's make this API change: Instead of separately
allocating a 'struct cyclic_info', make the users embed such an
instance in their own structure, and make the convention that the
callback simply receives the 'struct cyclic_info *', from which the
clients can get their own data using the container_of() macro.
This has a number of advantages.
First, it means cyclic_register() simply cannot fail, simplifying the
code. The necessary storage will simply be allocated automatically
when the client's own structure is allocated (often via
uclass_priv_auto or similar).
Second, code for which CONFIG_CYCLIC is just an option can more easily
be written without #ifdefs, if we just provide an empty struct
cyclic_info {}. For example, the nested CONFIG_IS_ENABLED()s in
https://lore.kernel.org/u-boot/20240316201416.211480-1-marek.vasut+renesas@mailbox.org/
are mostly due to the existence of the 'struct cyclic_info *' member
being guarded by #ifdef CONFIG_CYCLIC.
And we do probably want to avoid the extra memory overhead of that
member when !CONFIG_CYCLIC. But that is automatic if, instead of a
'struct cyclic_info *', one simply embeds a 'struct cyclic_info',
which will have size 0 when !CONFIG_CYCLIC. Also, the no-op
cyclic_register() function can just unconditionally be called, and the
compiler will see that (1) the callback is referenced, so not emit a
warning for a maybe-unused function and (2) see that it can actually
never be reached, so not emit any code for it.
Reviewed-by: Stefan Roese <sr@denx.de>
Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
56 lines
1.9 KiB
ReStructuredText
56 lines
1.9 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0+
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Cyclic functions
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================
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The cyclic function execution infrastruture provides a way to periodically
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execute code, e.g. every 100ms. Examples for such functions might be LED
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blinking etc. The functions that are hooked into this cyclic list should
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be small timewise as otherwise the execution of the other code that relies
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on a high frequent polling (e.g. UART rx char ready check) might be
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delayed too much. To detect cyclic functions with an excessive execution
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time, the Kconfig option `CONFIG_CYCLIC_MAX_CPU_TIME_US` was introduced.
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It defines the maximum allowable execution time for such a cyclic function. The
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first time the execution of a cyclic function exceeds this interval, a warning
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will be displayed indicating the problem to the user.
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Registering a cyclic function
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-----------------------------
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To register a cyclic function, use something like this::
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struct donkey {
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struct cyclic_info cyclic;
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void (*say)(const char *s);
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};
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static void cyclic_demo(struct cyclic_info *c)
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{
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struct donkey *donkey = container_of(c, struct donkey, cyclic);
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donkey->say("Are we there yet?");
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}
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int donkey_init(void)
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{
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struct donkey *donkey;
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/* Initialize donkey ... */
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/* Register demo cyclic function */
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cyclic_register(&donkey->cyclic, cyclic_demo, 10 * 1000, "cyclic_demo");
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return 0;
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}
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This will register the function `cyclic_demo()` to be periodically
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executed all 10ms.
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How is this cyclic functionality integrated / executed?
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--------------------------------------------------------
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The cyclic infrastructure integrates the main function responsible for
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calling all registered cyclic functions cyclic_run() into the common
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WATCHDOG_RESET macro. This guarantees that cyclic_run() is executed
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very often, which is necessary for the cyclic functions to get scheduled
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and executed at their configured periods.
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