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, 5 insertions, 7 deletions

diff --git a/cmd/cyclic.c b/cmd/cyclic.c
index 40e966de9aa..339dd4a7bce 100644
--- a/cmd/cyclic.c
+++ b/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);