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
Signed-off-by: Jerome Brunet <jbru...@baylibre.com>
---
drivers/clk/clk.c | 167 ++++++++++++++++++++++++++++++++++++++++++++++++++++
include/linux/clk.h | 57 ++++++++++++++++++
2 files changed, 224 insertions(+)
diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index f990ef127a83..cbfff541ec8a 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -85,6 +85,7 @@ struct clk {
const char *con_id;
unsigned long min_rate;
unsigned long max_rate;
+ unsigned int exclusive_count;
struct hlist_node clks_node;
};
@@ -512,6 +513,45 @@ 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);
@@ -539,6 +579,36 @@ 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, and do not
+ * return error status.
+ */
+void clk_rate_exclusive_get(struct clk *clk)
+{
+ if (!clk)
+ return;
+
+ clk_prepare_lock();
+ clk_core_rate_protect(clk->core);
+ clk->exclusive_count++;
+ clk_prepare_unlock();
+}
+EXPORT_SYMBOL_GPL(clk_rate_exclusive_get);
+
static void clk_core_unprepare(struct clk_core *core)
{
lockdep_assert_held(&prepare_lock);
@@ -929,6 +999,12 @@ 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) {
@@ -1045,10 +1121,17 @@ 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)
@@ -1769,8 +1852,14 @@ 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;
@@ -1778,6 +1867,50 @@ int clk_set_rate(struct clk *clk, unsigned long rate)
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.
+ *
+ * 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
* @min: desired minimum clock rate in Hz, inclusive
@@ -1801,12 +1934,18 @@ 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;
@@ -2010,8 +2149,16 @@ 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;
@@ -2073,7 +2220,15 @@ 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;
@@ -3086,6 +3241,18 @@ 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..fdababf80420 100644
--- a/include/linux/clk.h
+++ b/include/linux/clk.h
@@ -331,6 +331,36 @@ 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.
+ */
+void 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.
@@ -473,6 +503,23 @@ 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
* @parent: parent clock source
@@ -583,6 +630,11 @@ 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 void clk_exclusive_get(struct clk *clk) {}
+
+static inline void clk_exclusive_put(struct clk *clk) {}
+
static inline int clk_enable(struct clk *clk)
{
return 0;
@@ -609,6 +661,11 @@ 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;
--
2.13.5
