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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 <maxime.ripard@free-electrons.com>
Acked-by: Michael Turquette <mturquette@baylibre.com>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Michael Turquette <mturquette@baylibre.com>
Link: lkml.kernel.org/r/20171201215200.23523-10-jbrunet@baylibre.com
This commit is contained in:
Jerome Brunet 2017-12-01 22:51:59 +01:00 committed by Michael Turquette
parent c5ce26edb4
commit 55e9b8b7b8
2 changed files with 234 additions and 0 deletions
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172
drivers/clk/clk.c
View File

@ -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)

62
include/linux/clk.h
View File

@ -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;