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>

board/Marvell/octeon_nic23/board.c

@@ -249,7 +249,7 @@ void board_configure_qlms(void)
  * read the incorrect device ID 0x9700 (reset value) instead of 0x9702
  * (restored value).
  */
-static void octeon_board_restore_pf(void *ctx)
+static void octeon_board_restore_pf(struct cyclic_info *c)
 {
 	union cvmx_spemx_flr_pf_stopreq stopreq;
 	static bool start_initialized[2] = {false, false};
@@ -357,10 +357,13 @@ int board_late_init(void)
 	board_configure_qlms();
 
 	/* Register cyclic function for PCIe FLR fixup */
-	cyclic = cyclic_register(octeon_board_restore_pf, 100,
-				 "pcie_flr_fix", NULL);
-	if (!cyclic)
+	cyclic = calloc(1, sizeof(*cyclic));
+	if (cyclic) {
+		cyclic_register(cyclic, octeon_board_restore_pf, 100,
+				"pcie_flr_fix");
+	} else {
 		printf("Registering of cyclic function failed\n");
+	}
 
 	return 0;
 }

cmd/cyclic.c

@@ -15,14 +15,16 @@
 #include <time.h>
 #include <vsprintf.h>
 #include <linux/delay.h>
+#include <linux/kernel.h>
 
 struct cyclic_demo_info {
+	struct cyclic_info cyclic;
 	uint delay_us;
 };
 
-static void cyclic_demo(void *ctx)
+static void cyclic_demo(struct cyclic_info *c)
 {
-	struct cyclic_demo_info *info = ctx;
+	struct cyclic_demo_info *info = container_of(c, struct cyclic_demo_info, cyclic);
 
 	/* Just a small dummy delay here */
 	udelay(info->delay_us);
@@ -32,7 +34,6 @@ static int do_cyclic_demo(struct cmd_tbl *cmdtp, int flag, int argc,
 			  char *const argv[])
 {
 	struct cyclic_demo_info *info;
-	struct cyclic_info *cyclic;
 	uint time_ms;
 
 	if (argc < 3)
@@ -48,10 +49,7 @@ static int do_cyclic_demo(struct cmd_tbl *cmdtp, int flag, int argc,
 	info->delay_us = simple_strtoul(argv[2], NULL, 0);
 
 	/* Register demo cyclic function */
-	cyclic = cyclic_register(cyclic_demo, time_ms * 1000, "cyclic_demo",
-				 info);
-	if (!cyclic)
-		printf("Registering of cyclic_demo failed\n");
+	cyclic_register(&info->cyclic, cyclic_demo, time_ms * 1000, "cyclic_demo");
 
 	printf("Registered function \"%s\" to be executed all %dms\n",
 	       "cyclic_demo", time_ms);

common/cyclic.c

@@ -26,34 +26,22 @@ struct hlist_head *cyclic_get_list(void)
 	return (struct hlist_head *)&gd->cyclic_list;
 }
 
-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)
 {
-	struct cyclic_info *cyclic;
-
-	cyclic = calloc(1, sizeof(struct cyclic_info));
-	if (!cyclic) {
-		pr_debug("Memory allocation error\n");
-		return NULL;
-	}
+	memset(cyclic, 0, sizeof(*cyclic));
 
 	/* Store values in struct */
 	cyclic->func = func;
-	cyclic->ctx = ctx;
 	cyclic->name = name;
 	cyclic->delay_us = delay_us;
 	cyclic->start_time_us = timer_get_us();
 	hlist_add_head(&cyclic->list, cyclic_get_list());
-
-	return cyclic;
 }
 
-int cyclic_unregister(struct cyclic_info *cyclic)
+void cyclic_unregister(struct cyclic_info *cyclic)
 {
 	hlist_del(&cyclic->list);
-	free(cyclic);
-
-	return 0;
 }
 
 void cyclic_run(void)
@@ -76,7 +64,7 @@ void cyclic_run(void)
 		if (time_after_eq64(now, cyclic->next_call)) {
 			/* Call cyclic function and account it's cpu-time */
 			cyclic->next_call = now + cyclic->delay_us;
-			cyclic->func(cyclic->ctx);
+			cyclic->func(cyclic);
 			cyclic->run_cnt++;
 			cpu_time = timer_get_us() - now;
 			cyclic->cpu_time_us += cpu_time;

doc/develop/cyclic.rst

@@ -19,20 +19,26 @@ Registering a cyclic function
 
 To register a cyclic function, use something like this::
 
-    static void cyclic_demo(void *ctx)
+    struct donkey {
+        struct cyclic_info cyclic;
+        void (*say)(const char *s);
+    };
+
+    static void cyclic_demo(struct cyclic_info *c)
     {
-        /* Just a small dummy delay here */
-        udelay(10);
+        struct donkey *donkey = container_of(c, struct donkey, cyclic);
+
+        donkey->say("Are we there yet?");
     }
-    
-    int board_init(void)
+
+    int donkey_init(void)
     {
-        struct cyclic_info *cyclic;
-        
+        struct donkey *donkey;
+
+        /* Initialize donkey ... */
+
         /* Register demo cyclic function */
-        cyclic = cyclic_register(cyclic_demo, 10 * 1000, "cyclic_demo", NULL);
-        if (!cyclic)
-        printf("Registering of cyclic_demo failed\n");
+        cyclic_register(&donkey->cyclic, cyclic_demo, 10 * 1000, "cyclic_demo");
         
         return 0;
     }

drivers/watchdog/wdt-uclass.c

@@ -17,12 +17,15 @@
 #include <asm/global_data.h>
 #include <dm/device-internal.h>
 #include <dm/lists.h>
+#include <linux/kernel.h>
 
 DECLARE_GLOBAL_DATA_PTR;
 
 #define WATCHDOG_TIMEOUT_SECS	(CONFIG_WATCHDOG_TIMEOUT_MSECS / 1000)
 
 struct wdt_priv {
+	/* The udevice owning this wdt_priv. */
+	struct udevice *dev;
 	/* Timeout, in seconds, to configure this device to. */
 	u32 timeout;
 	/*
@@ -40,18 +43,17 @@ struct wdt_priv {
 	/* autostart */
 	bool autostart;
 
-	struct cyclic_info *cyclic;
+	struct cyclic_info cyclic;
 };
 
-static void wdt_cyclic(void *ctx)
+static void wdt_cyclic(struct cyclic_info *c)
 {
-	struct udevice *dev = ctx;
-	struct wdt_priv *priv;
+	struct wdt_priv *priv = container_of(c, struct wdt_priv, cyclic);
+	struct udevice *dev = priv->dev;
 
 	if (!device_active(dev))
 		return;
 
-	priv = dev_get_uclass_priv(dev);
 	if (!priv->running)
 		return;
 
@@ -124,20 +126,14 @@ int wdt_start(struct udevice *dev, u64 timeout_ms, ulong flags)
 		memset(str, 0, 16);
 		if (IS_ENABLED(CONFIG_WATCHDOG)) {
 			if (priv->running)
-				cyclic_unregister(priv->cyclic);
+				cyclic_unregister(&priv->cyclic);
 
 			/* Register the watchdog driver as a cyclic function */
-			priv->cyclic = cyclic_register(wdt_cyclic,
-						       priv->reset_period * 1000,
-						       dev->name, dev);
-			if (!priv->cyclic) {
-				printf("cyclic_register for %s failed\n",
-				       dev->name);
-				return -ENODEV;
-			} else {
-				snprintf(str, 16, "every %ldms",
-					 priv->reset_period);
-			}
+			cyclic_register(&priv->cyclic, wdt_cyclic,
+					priv->reset_period * 1000,
+					dev->name);
+
+			snprintf(str, 16, "every %ldms", priv->reset_period);
 		}
 
 		priv->running = true;
@@ -162,7 +158,7 @@ int wdt_stop(struct udevice *dev)
 		struct wdt_priv *priv = dev_get_uclass_priv(dev);
 
 		if (IS_ENABLED(CONFIG_WATCHDOG) && priv->running)
-			cyclic_unregister(priv->cyclic);
+			cyclic_unregister(&priv->cyclic);
 
 		priv->running = false;
 	}
@@ -262,6 +258,7 @@ static int wdt_pre_probe(struct udevice *dev)
 			autostart = true;
 	}
 	priv = dev_get_uclass_priv(dev);
+	priv->dev = dev;
 	priv->timeout = timeout;
 	priv->reset_period = reset_period;
 	priv->autostart = autostart;

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)

test/common/cyclic.c

@@ -12,22 +12,27 @@
 #include <linux/delay.h>
 
 /* Test that cyclic function is called */
-static bool cyclic_active = false;
+static struct cyclic_test {
+	struct cyclic_info cyclic;
+	bool called;
+} cyclic_test;
 
-static void cyclic_test(void *ctx)
+static void test_cb(struct cyclic_info *c)
 {
-	cyclic_active = true;
+	struct cyclic_test *t = container_of(c, struct cyclic_test, cyclic);
+	t->called = true;
 }
 
 static int dm_test_cyclic_running(struct unit_test_state *uts)
 {
-	cyclic_active = false;
-	ut_assertnonnull(cyclic_register(cyclic_test, 10 * 1000, "cyclic_demo",
-					 NULL));
+	cyclic_test.called = false;
+	cyclic_register(&cyclic_test.cyclic, test_cb, 10 * 1000, "cyclic_test");
 
 	/* Execute all registered cyclic functions */
 	schedule();
-	ut_asserteq(true, cyclic_active);
+	ut_asserteq(true, cyclic_test.called);
+
+	cyclic_unregister(&cyclic_test.cyclic);
 
 	return 0;
 }