From 55e9b8b7b806ec3f9a8817e13596682a5981c19c Mon Sep 17 00:00:00 2001 From: Jerome Brunet Date: Fri, 1 Dec 2017 22:51:59 +0100 Subject: [PATCH] clk: add clk_rate_exclusive api Using clock rate protection, we can now provide a way for clock consumer to claim exclusive control over the rate of a producer So far, rate change operations have been a "last write wins" affair. This changes allows drivers to explicitly protect against this behavior, if required. Of course, if exclusivity over a producer is claimed more than once, the rate is effectively locked as exclusivity cannot be preempted Tested-by: Maxime Ripard Acked-by: Michael Turquette Signed-off-by: Jerome Brunet Signed-off-by: Michael Turquette Link: lkml.kernel.org/r/20171201215200.23523-10-jbrunet@baylibre.com --- drivers/clk/clk.c | 172 ++++++++++++++++++++++++++++++++++++++++++++ include/linux/clk.h | 62 ++++++++++++++++ 2 files changed, 234 insertions(+) diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c index f6fe5e5595ca..8e728f395b54 100644 --- a/drivers/clk/clk.c +++ b/drivers/clk/clk.c @@ -87,6 +87,7 @@ struct clk { const char *con_id; unsigned long min_rate; unsigned long max_rate; + unsigned int exclusive_count; struct hlist_node clks_node; }; @@ -565,6 +566,45 @@ static int clk_core_rate_nuke_protect(struct clk_core *core) return ret; } +/** + * clk_rate_exclusive_put - release exclusivity over clock rate control + * @clk: the clk over which the exclusivity is released + * + * clk_rate_exclusive_put() completes a critical section during which a clock + * consumer cannot tolerate any other consumer making any operation on the + * clock which could result in a rate change or rate glitch. Exclusive clocks + * cannot have their rate changed, either directly or indirectly due to changes + * further up the parent chain of clocks. As a result, clocks up parent chain + * also get under exclusive control of the calling consumer. + * + * If exlusivity is claimed more than once on clock, even by the same consumer, + * the rate effectively gets locked as exclusivity can't be preempted. + * + * Calls to clk_rate_exclusive_put() must be balanced with calls to + * clk_rate_exclusive_get(). Calls to this function may sleep, and do not return + * error status. + */ +void clk_rate_exclusive_put(struct clk *clk) +{ + if (!clk) + return; + + clk_prepare_lock(); + + /* + * if there is something wrong with this consumer protect count, stop + * here before messing with the provider + */ + if (WARN_ON(clk->exclusive_count <= 0)) + goto out; + + clk_core_rate_unprotect(clk->core); + clk->exclusive_count--; +out: + clk_prepare_unlock(); +} +EXPORT_SYMBOL_GPL(clk_rate_exclusive_put); + static void clk_core_rate_protect(struct clk_core *core) { lockdep_assert_held(&prepare_lock); @@ -592,6 +632,38 @@ static void clk_core_rate_restore_protect(struct clk_core *core, int count) core->protect_count = count; } +/** + * clk_rate_exclusive_get - get exclusivity over the clk rate control + * @clk: the clk over which the exclusity of rate control is requested + * + * clk_rate_exlusive_get() begins a critical section during which a clock + * consumer cannot tolerate any other consumer making any operation on the + * clock which could result in a rate change or rate glitch. Exclusive clocks + * cannot have their rate changed, either directly or indirectly due to changes + * further up the parent chain of clocks. As a result, clocks up parent chain + * also get under exclusive control of the calling consumer. + * + * If exlusivity is claimed more than once on clock, even by the same consumer, + * the rate effectively gets locked as exclusivity can't be preempted. + * + * Calls to clk_rate_exclusive_get() should be balanced with calls to + * clk_rate_exclusive_put(). Calls to this function may sleep. + * Returns 0 on success, -EERROR otherwise + */ +int clk_rate_exclusive_get(struct clk *clk) +{ + if (!clk) + return 0; + + clk_prepare_lock(); + clk_core_rate_protect(clk->core); + clk->exclusive_count++; + clk_prepare_unlock(); + + return 0; +} +EXPORT_SYMBOL_GPL(clk_rate_exclusive_get); + static void clk_core_unprepare(struct clk_core *core) { lockdep_assert_held(&prepare_lock); @@ -988,6 +1060,12 @@ static int clk_core_determine_round_nolock(struct clk_core *core, if (!core) return 0; + /* + * At this point, core protection will be disabled if + * - if the provider is not protected at all + * - if the calling consumer is the only one which has exclusivity + * over the provider + */ if (clk_core_rate_is_protected(core)) { req->rate = core->rate; } else if (core->ops->determine_rate) { @@ -1104,10 +1182,17 @@ long clk_round_rate(struct clk *clk, unsigned long rate) clk_prepare_lock(); + if (clk->exclusive_count) + clk_core_rate_unprotect(clk->core); + clk_core_get_boundaries(clk->core, &req.min_rate, &req.max_rate); req.rate = rate; ret = clk_core_round_rate_nolock(clk->core, &req); + + if (clk->exclusive_count) + clk_core_rate_protect(clk->core); + clk_prepare_unlock(); if (ret) @@ -1843,14 +1928,67 @@ int clk_set_rate(struct clk *clk, unsigned long rate) /* prevent racing with updates to the clock topology */ clk_prepare_lock(); + if (clk->exclusive_count) + clk_core_rate_unprotect(clk->core); + ret = clk_core_set_rate_nolock(clk->core, rate); + if (clk->exclusive_count) + clk_core_rate_protect(clk->core); + clk_prepare_unlock(); return ret; } EXPORT_SYMBOL_GPL(clk_set_rate); +/** + * clk_set_rate_exclusive - specify a new rate get exclusive control + * @clk: the clk whose rate is being changed + * @rate: the new rate for clk + * + * This is a combination of clk_set_rate() and clk_rate_exclusive_get() + * within a critical section + * + * This can be used initially to ensure that at least 1 consumer is + * statisfied when several consumers are competing for exclusivity over the + * same clock provider. + * + * The exclusivity is not applied if setting the rate failed. + * + * Calls to clk_rate_exclusive_get() should be balanced with calls to + * clk_rate_exclusive_put(). + * + * Returns 0 on success, -EERROR otherwise. + */ +int clk_set_rate_exclusive(struct clk *clk, unsigned long rate) +{ + int ret; + + if (!clk) + return 0; + + /* prevent racing with updates to the clock topology */ + clk_prepare_lock(); + + /* + * The temporary protection removal is not here, on purpose + * This function is meant to be used instead of clk_rate_protect, + * so before the consumer code path protect the clock provider + */ + + ret = clk_core_set_rate_nolock(clk->core, rate); + if (!ret) { + clk_core_rate_protect(clk->core); + clk->exclusive_count++; + } + + clk_prepare_unlock(); + + return ret; +} +EXPORT_SYMBOL_GPL(clk_set_rate_exclusive); + /** * clk_set_rate_range - set a rate range for a clock source * @clk: clock source @@ -1875,12 +2013,18 @@ int clk_set_rate_range(struct clk *clk, unsigned long min, unsigned long max) clk_prepare_lock(); + if (clk->exclusive_count) + clk_core_rate_unprotect(clk->core); + if (min != clk->min_rate || max != clk->max_rate) { clk->min_rate = min; clk->max_rate = max; ret = clk_core_set_rate_nolock(clk->core, clk->core->req_rate); } + if (clk->exclusive_count) + clk_core_rate_protect(clk->core); + clk_prepare_unlock(); return ret; @@ -2091,8 +2235,16 @@ int clk_set_parent(struct clk *clk, struct clk *parent) return 0; clk_prepare_lock(); + + if (clk->exclusive_count) + clk_core_rate_unprotect(clk->core); + ret = clk_core_set_parent_nolock(clk->core, parent ? parent->core : NULL); + + if (clk->exclusive_count) + clk_core_rate_protect(clk->core); + clk_prepare_unlock(); return ret; @@ -2154,7 +2306,15 @@ int clk_set_phase(struct clk *clk, int degrees) degrees += 360; clk_prepare_lock(); + + if (clk->exclusive_count) + clk_core_rate_unprotect(clk->core); + ret = clk_core_set_phase_nolock(clk->core, degrees); + + if (clk->exclusive_count) + clk_core_rate_protect(clk->core); + clk_prepare_unlock(); return ret; @@ -3175,6 +3335,18 @@ void __clk_put(struct clk *clk) clk_prepare_lock(); + /* + * Before calling clk_put, all calls to clk_rate_exclusive_get() from a + * given user should be balanced with calls to clk_rate_exclusive_put() + * and by that same consumer + */ + if (WARN_ON(clk->exclusive_count)) { + /* We voiced our concern, let's sanitize the situation */ + clk->core->protect_count -= (clk->exclusive_count - 1); + clk_core_rate_unprotect(clk->core); + clk->exclusive_count = 0; + } + hlist_del(&clk->clks_node); if (clk->min_rate > clk->core->req_rate || clk->max_rate < clk->core->req_rate) diff --git a/include/linux/clk.h b/include/linux/clk.h index 12c96d94d1fa..4c4ef9f34db3 100644 --- a/include/linux/clk.h +++ b/include/linux/clk.h @@ -331,6 +331,38 @@ struct clk *devm_clk_get(struct device *dev, const char *id); */ struct clk *devm_get_clk_from_child(struct device *dev, struct device_node *np, const char *con_id); +/** + * clk_rate_exclusive_get - get exclusivity over the rate control of a + * producer + * @clk: clock source + * + * This function allows drivers to get exclusive control over the rate of a + * provider. It prevents any other consumer to execute, even indirectly, + * opereation which could alter the rate of the provider or cause glitches + * + * If exlusivity is claimed more than once on clock, even by the same driver, + * the rate effectively gets locked as exclusivity can't be preempted. + * + * Must not be called from within atomic context. + * + * Returns success (0) or negative errno. + */ +int clk_rate_exclusive_get(struct clk *clk); + +/** + * clk_rate_exclusive_put - release exclusivity over the rate control of a + * producer + * @clk: clock source + * + * This function allows drivers to release the exclusivity it previously got + * from clk_rate_exclusive_get() + * + * The caller must balance the number of clk_rate_exclusive_get() and + * clk_rate_exclusive_put() calls. + * + * Must not be called from within atomic context. + */ +void clk_rate_exclusive_put(struct clk *clk); /** * clk_enable - inform the system when the clock source should be running. @@ -472,6 +504,23 @@ long clk_round_rate(struct clk *clk, unsigned long rate); */ int clk_set_rate(struct clk *clk, unsigned long rate); +/** + * clk_set_rate_exclusive- set the clock rate and claim exclusivity over + * clock source + * @clk: clock source + * @rate: desired clock rate in Hz + * + * This helper function allows drivers to atomically set the rate of a producer + * and claim exclusivity over the rate control of the producer. + * + * It is essentially a combination of clk_set_rate() and + * clk_rate_exclusite_get(). Caller must balance this call with a call to + * clk_rate_exclusive_put() + * + * Returns success (0) or negative errno. + */ +int clk_set_rate_exclusive(struct clk *clk, unsigned long rate); + /** * clk_has_parent - check if a clock is a possible parent for another * @clk: clock source @@ -583,6 +632,14 @@ static inline void clk_bulk_put(int num_clks, struct clk_bulk_data *clks) {} static inline void devm_clk_put(struct device *dev, struct clk *clk) {} + +static inline int clk_rate_exclusive_get(struct clk *clk) +{ + return 0; +} + +static inline void clk_rate_exclusive_put(struct clk *clk) {} + static inline int clk_enable(struct clk *clk) { return 0; @@ -609,6 +666,11 @@ static inline int clk_set_rate(struct clk *clk, unsigned long rate) return 0; } +static inline int clk_set_rate_exclusive(struct clk *clk, unsigned long rate) +{ + return 0; +} + static inline long clk_round_rate(struct clk *clk, unsigned long rate) { return 0;