cyclic: make clients embed a struct cyclic_info in their own data structure

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>

1 files changed, 18 insertions, 17 deletions

diff --git a/include/cyclic.h b/include/cyclic.h
index 38946216fb8..2c3d383c5ef 100644
--- a/include/cyclic.h
+++ b/include/cyclic.h
@@ -18,7 +18,6 @@
  * struct cyclic_info - Information about cyclic execution function
  *
  * @func: Function to call periodically
- * @ctx: Context pointer to get passed to this function
  * @name: Name of the cyclic function, e.g. shown in the commands
  * @delay_ns: Delay is ns after which this function shall get executed
  * @start_time_us: Start time in us, when this function started its execution
@@ -27,10 +26,12 @@
  * @next_call: Next time in us, when the function shall be executed again
  * @list: List node
  * @already_warned: Flag that we've warned about exceeding CPU time usage
+ *
+ * When !CONFIG_CYCLIC, this struct is empty.
  */
 struct cyclic_info {
-	void (*func)(void *ctx);
-	void *ctx;
+#if defined(CONFIG_CYCLIC)
+	void (*func)(struct cyclic_info *c);
 	const char *name;
 	uint64_t delay_us;
 	uint64_t start_time_us;
@@ -39,31 +40,34 @@ struct cyclic_info {
 	uint64_t next_call;
 	struct hlist_node list;
 	bool already_warned;
+#endif
 };
 
 /** Function type for cyclic functions */
-typedef void (*cyclic_func_t)(void *ctx);
+typedef void (*cyclic_func_t)(struct cyclic_info *c);
 
 #if defined(CONFIG_CYCLIC)
 /**
  * cyclic_register - Register a new cyclic function
  *
+ * @cyclic: Cyclic info structure
  * @func: Function to call periodically
  * @delay_us: Delay is us after which this function shall get executed
  * @name: Cyclic function name/id
- * @ctx: Context to pass to the function
- * @return: pointer to cyclic_struct if OK, NULL on error
+ *
+ * The function @func will be called with @cyclic as its
+ * argument. @cyclic will usually be embedded in some device-specific
+ * structure, which the callback can retrieve using container_of().
  */
-struct cyclic_info *cyclic_register(cyclic_func_t func, uint64_t delay_us,
-				    const char *name, void *ctx);
+void cyclic_register(struct cyclic_info *cyclic, cyclic_func_t func,
+		     uint64_t delay_us, const char *name);
 
 /**
  * cyclic_unregister - Unregister a cyclic function
  *
  * @cyclic: Pointer to cyclic_struct of the function that shall be removed
- * @return: 0 if OK, -ve on error
  */
-int cyclic_unregister(struct cyclic_info *cyclic);
+void cyclic_unregister(struct cyclic_info *cyclic);
 
 /**
  * cyclic_unregister_all() - Clean up cyclic functions
@@ -97,17 +101,14 @@ void cyclic_run(void);
  */
 void schedule(void);
 #else
-static inline struct cyclic_info *cyclic_register(cyclic_func_t func,
-						  uint64_t delay_us,
-						  const char *name,
-						  void *ctx)
+
+static inline void cyclic_register(struct cyclic_info *cyclic, cyclic_func_t func,
+				   uint64_t delay_us, const char *name)
 {
-	return NULL;
 }
 
-static inline int cyclic_unregister(struct cyclic_info *cyclic)
+static inline void cyclic_unregister(struct cyclic_info *cyclic)
 {
-	return 0;
 }
 
 static inline void cyclic_run(void)