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Commit 55e9b8b7 authored by Jerome Brunet's avatar Jerome Brunet Committed by Michael Turquette
Browse files

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: default avatarMaxime Ripard <maxime.ripard@free-electrons.com>
Acked-by: default avatarMichael Turquette <mturquette@baylibre.com>
Signed-off-by: default avatarJerome Brunet <jbrunet@baylibre.com>
Signed-off-by: default avatarMichael Turquette <mturquette@baylibre.com>
Link: lkml.kernel.org/r/20171201215200.23523-10-jbrunet@baylibre.com
parent c5ce26ed

drivers/clk/clk.c

+172 −0
Original line number Diff line number Diff line
@@ -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)

include/linux/clk.h

+62 −0
Original line number Diff line number Diff line
@@ -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;