From 2dbd9101b9910fe2c0fc2c23bc4d13a2604e9cca Mon Sep 17 00:00:00 2001 From: Rasmus Villemoes Date: Wed, 7 May 2025 12:58:19 +0200 Subject: [PATCH 1/3] cyclic: make cyclic_unregister() idempotent Make cyclic_unregister() safe to call with an already unregistered, or possibly never registered, struct cyclic_info. This is similar to how the various timer APIs in the linux kernel work (they all allow calling delete/cancel/... on an inactive timer object). This means callers don't have to separately keep track of whether their cyclic callback is registered or not, and avoids them trying to peek into the struct cyclic_info for that information - which leads to somewhat ugly code as it would have to be guarded by ifdef CONFIG_CYCLIC. Signed-off-by: Rasmus Villemoes Reviewed-by: Stefan Roese --- common/cyclic.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/common/cyclic.c b/common/cyclic.c index b695f092f52..75662d9f613 100644 --- a/common/cyclic.c +++ b/common/cyclic.c @@ -28,6 +28,18 @@ struct hlist_head *cyclic_get_list(void) return (struct hlist_head *)&gd->cyclic_list; } +static bool cyclic_is_registered(const struct cyclic_info *cyclic) +{ + const struct cyclic_info *c; + + hlist_for_each_entry(c, cyclic_get_list(), list) { + if (c == cyclic) + return true; + } + + return false; +} + void cyclic_register(struct cyclic_info *cyclic, cyclic_func_t func, uint64_t delay_us, const char *name) { @@ -43,6 +55,9 @@ void cyclic_register(struct cyclic_info *cyclic, cyclic_func_t func, void cyclic_unregister(struct cyclic_info *cyclic) { + if (!cyclic_is_registered(cyclic)) + return; + hlist_del(&cyclic->list); } From 5265143ac7356b94ace3e26a9fd6df17774b189b Mon Sep 17 00:00:00 2001 From: Rasmus Villemoes Date: Wed, 7 May 2025 12:58:20 +0200 Subject: [PATCH 2/3] cyclic: make cyclic_register safe to call on already-registered info Now that cyclic_unregister() is safe to call on a not-registered cyclic_info, we can make cyclic_register() behave like the mod_timer() and hrtimer_start() APIs in linux, in that they don't distinguish between whether the timer was already enabled or not; from the point of the call it is, with whatever timeout/period is set in that most recent call. This avoids users of the cyclic API from separately keeping track of whether their callback is already registered or not, and even if they know it is, can be used for changing the period (and/or the callback function) without first doing unregister(). See also this recent'ish message from kernel maintainer Thomas Gleixner on that API design for timer frameworks: https://lore.kernel.org/lkml/87ikn6sibi.ffs@tglx/ First of all the question is whether add() and mod() are really valuable distinctions. I'm not convinced at all. Back then, when we introduced hrtimers, we came to the conclusion that hrtimer_start() is sufficient. Signed-off-by: Rasmus Villemoes Reviewed-by: Stefan Roese --- common/cyclic.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/common/cyclic.c b/common/cyclic.c index 75662d9f613..ec952a01ee1 100644 --- a/common/cyclic.c +++ b/common/cyclic.c @@ -43,6 +43,8 @@ static bool cyclic_is_registered(const struct cyclic_info *cyclic) void cyclic_register(struct cyclic_info *cyclic, cyclic_func_t func, uint64_t delay_us, const char *name) { + cyclic_unregister(cyclic); + memset(cyclic, 0, sizeof(*cyclic)); /* Store values in struct */ From 6f0a3cd7bcdd4ce25b5ad253a6ebad88d4b94fbe Mon Sep 17 00:00:00 2001 From: Rasmus Villemoes Date: Wed, 7 May 2025 12:58:21 +0200 Subject: [PATCH 3/3] cyclic: document new guarantees for cyclic_(un)register Signed-off-by: Rasmus Villemoes Reviewed-by: Stefan Roese --- doc/develop/cyclic.rst | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/doc/develop/cyclic.rst b/doc/develop/cyclic.rst index 6f1da6f0d9b..a99b17052f5 100644 --- a/doc/develop/cyclic.rst +++ b/doc/develop/cyclic.rst @@ -54,3 +54,16 @@ responsible for calling all registered cyclic functions, into the common schedule() function. This guarantees that cyclic_run() is executed very often, which is necessary for the cyclic functions to get scheduled and executed at their configured periods. + +Idempotence +----------- + +Both the cyclic_register() and cyclic_unregister() functions are safe +to call on any struct cyclic_info, regardless of whether that instance +is already registered or not. + +More specifically, calling cyclic_unregister() with a cyclic_info +which is not currently registered is a no-op, while calling +cyclic_register() with a cyclic_info which is currently registered +results in it being automatically unregistered, and then registered +with the new callback function and timeout parameters.