[PATCH 00/10] clk: implement clock rate protection mechanism

[PATCH 00/10] clk: implement clock rate protection mechanism

[Jerome Brunet]

This Patchset is related the RFC [0] and the discussion around
CLK_SET_RATE_GATE available here [1]

The goal of this patchset is to provide a way for consumers to inform the
system that they depend on the rate of the clock source and can't tolerate
other consumers changing the rate or causing glitches.

With this series there is 3 use-case:
 - the provider is not protected: nothing changes
 - the provider is protected by only 1 consumer (and only once), then only
   this consumer will be able to alter the rate of the clock, as it is the only
   one depending on it.
 - If the provider is protected more than once, or by the provider itself, the rate
   is basically locked.

Changes since RFC:
 - s/clk_protect/clk_rate_protect
 - Request rework around core_nolock function
 - Add clk_set_rate_protect
 - Reword clk_rate_protect and clk_unprotect documentation
 - Add few comments to explain the code
 - Add 2 last patches to fix users of CLK_SET_RATE_GATE

The last 2 patches provide the same functionnality for providers themself by
fixing the issue with CLK_SET_RATE_GATE.

This was tested with the audio use case mentioned in [1]

[0]: http://lkml.kernel.org/r/20170321183330.26722-1-jbrunet at baylibre.com
[1]: http://lkml.kernel.org/r/148942423440.82235.17188153691656009029 at resonance

Jerome Brunet (10):
  clk: take the prepare lock out of clk_core_set_parent
  clk: add clk_core_set_phase_nolock function
  clk: rework calls to round and determine rate callbacks
  clk: add support for clock protection
  clk: add clk_set_rate_protect
  clk: rollback set_rate_range changes on failure
  clk: cosmetic changes to clk_summary debugfs entry
  clk: fix incorrect usage of ENOSYS
  clk: fix CLK_SET_RATE_GATE with clock rate protection
  clk: move CLK_SET_RATE_GATE protection from prepare to enable

 drivers/clk/clk.c            | 397 +++++++++++++++++++++++++++++++++++--------
 include/linux/clk-provider.h |   1 +
 include/linux/clk.h          |  43 +++++
 3 files changed, 373 insertions(+), 68 deletions(-)

-- 
2.9.4

[PATCH 01/10] clk: take the prepare lock out of clk_core_set_paren

[Jerome Brunet]

Rework set_parent core function so it can be called when the prepare lock
is already held by the caller.

This rework is done to ease the integration of the "protected" clock
functionality.

Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
---
 drivers/clk/clk.c | 39 ++++++++++++++++++---------------------
 1 file changed, 18 insertions(+), 21 deletions(-)

diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index fc58c52a26b4..f5c371532509 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -1787,7 +1787,8 @@ bool clk_has_parent(struct clk *clk, struct clk *parent)
 }
 EXPORT_SYMBOL_GPL(clk_has_parent);
 
-static int clk_core_set_parent(struct clk_core *core, struct clk_core *parent)
+static int clk_core_set_parent_nolock(struct clk_core *core,
+				      struct clk_core *parent)
 {
 	int ret = 0;
 	int p_index = 0;
@@ -1796,23 +1797,16 @@ static int clk_core_set_parent(struct clk_core *core, struct clk_core *parent)
 	if (!core)
 		return 0;
 
-	/* prevent racing with updates to the clock topology */
-	clk_prepare_lock();
-
 	if (core->parent == parent)
-		goto out;
+		return 0;
 
 	/* verify ops for for multi-parent clks */
-	if ((core->num_parents > 1) && (!core->ops->set_parent)) {
-		ret = -ENOSYS;
-		goto out;
-	}
+	if ((core->num_parents > 1) && (!core->ops->set_parent))
+		return -ENOSYS;
 
 	/* check that we are allowed to re-parent if the clock is in use */
-	if ((core->flags & CLK_SET_PARENT_GATE) && core->prepare_count) {
-		ret = -EBUSY;
-		goto out;
-	}
+	if ((core->flags & CLK_SET_PARENT_GATE) && core->prepare_count)
+		return -EBUSY;
 
 	/* try finding the new parent index */
 	if (parent) {
@@ -1820,8 +1814,7 @@ static int clk_core_set_parent(struct clk_core *core, struct clk_core *parent)
 		if (p_index < 0) {
 			pr_debug("%s: clk %s can not be parent of clk %s\n",
 					__func__, parent->name, core->name);
-			ret = p_index;
-			goto out;
+			return p_index;
 		}
 		p_rate = parent->rate;
 	}
@@ -1831,7 +1824,7 @@ static int clk_core_set_parent(struct clk_core *core, struct clk_core *parent)
 
 	/* abort if a driver objects */
 	if (ret & NOTIFY_STOP_MASK)
-		goto out;
+		return ret;
 
 	/* do the re-parent */
 	ret = __clk_set_parent(core, parent, p_index);
@@ -1844,9 +1837,6 @@ static int clk_core_set_parent(struct clk_core *core, struct clk_core *parent)
 		__clk_recalc_accuracies(core);
 	}
 
-out:
-	clk_prepare_unlock();
-
 	return ret;
 }
 
@@ -1869,10 +1859,17 @@ static int clk_core_set_parent(struct clk_core *core, struct clk_core *parent)
  */
 int clk_set_parent(struct clk *clk, struct clk *parent)
 {
+	int ret;
+
 	if (!clk)
 		return 0;
 
-	return clk_core_set_parent(clk->core, parent ? parent->core : NULL);
+	clk_prepare_lock();
+	ret = clk_core_set_parent_nolock(clk->core,
+					 parent ? parent->core : NULL);
+	clk_prepare_unlock();
+
+	return ret;
 }
 EXPORT_SYMBOL_GPL(clk_set_parent);
 
@@ -2753,7 +2750,7 @@ void clk_unregister(struct clk *clk)
 		/* Reparent all children to the orphan list. */
 		hlist_for_each_entry_safe(child, t, &clk->core->children,
 					  child_node)
-			clk_core_set_parent(child, NULL);
+			clk_core_set_parent_nolock(child, NULL);
 	}
 
 	hlist_del_init(&clk->core->child_node);
-- 
2.9.4

[PATCH 02/10] clk: add clk_core_set_phase_nolock function

[Jerome Brunet]

Create a core function for set_phase, as it is done for set_rate and
set_parent.

This rework is done to ease the integration of "protected" clock
functionality.

Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
---
 drivers/clk/clk.c | 31 +++++++++++++++++++------------
 1 file changed, 19 insertions(+), 12 deletions(-)

diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index f5c371532509..6031fada37f9 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -1873,6 +1873,23 @@ int clk_set_parent(struct clk *clk, struct clk *parent)
 }
 EXPORT_SYMBOL_GPL(clk_set_parent);
 
+static int clk_core_set_phase_nolock(struct clk_core *core, int degrees)
+{
+	int ret = -EINVAL;
+
+	if (!core)
+		return 0;
+
+	trace_clk_set_phase(clk->core, degrees);
+
+	if (core->ops->set_phase)
+		ret = core->ops->set_phase(core->hw, degrees);
+
+	trace_clk_set_phase_complete(core, degrees);
+
+	return ret;
+}
+
 /**
  * clk_set_phase - adjust the phase shift of a clock signal
  * @clk: clock signal source
@@ -1895,7 +1912,7 @@ EXPORT_SYMBOL_GPL(clk_set_parent);
  */
 int clk_set_phase(struct clk *clk, int degrees)
 {
-	int ret = -EINVAL;
+	int ret;
 
 	if (!clk)
 		return 0;
@@ -1906,17 +1923,7 @@ int clk_set_phase(struct clk *clk, int degrees)
 		degrees += 360;
 
 	clk_prepare_lock();
-
-	trace_clk_set_phase(clk->core, degrees);
-
-	if (clk->core->ops->set_phase)
-		ret = clk->core->ops->set_phase(clk->core->hw, degrees);
-
-	trace_clk_set_phase_complete(clk->core, degrees);
-
-	if (!ret)
-		clk->core->phase = degrees;
-
+	ret = clk_core_set_phase_nolock(clk->core, degrees);
 	clk_prepare_unlock();
 
 	return ret;
-- 
2.9.4

[PATCH 03/10] clk: rework calls to round and determine rate callbacks

[Jerome Brunet]

Rework the way the callbacks round_rate and determine_rate are called. The
goal is to do this at a single point and make it easier to add conditions
before calling them.

This rework is done to ease the integration of "protected" clock
functionality.

Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
---
 drivers/clk/clk.c | 78 +++++++++++++++++++++++++++++++------------------------
 1 file changed, 44 insertions(+), 34 deletions(-)

diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index 6031fada37f9..100f72472e10 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -833,16 +833,34 @@ static int clk_disable_unused(void)
 }
 late_initcall_sync(clk_disable_unused);
 
-static int clk_core_round_rate_nolock(struct clk_core *core,
-				      struct clk_rate_request *req)
+static int clk_core_determine_round(struct clk_core *core,
+				    struct clk_rate_request *req)
 {
-	struct clk_core *parent;
 	long rate;
 
-	lockdep_assert_held(&prepare_lock);
+	if (core->ops->determine_rate) {
+		return core->ops->determine_rate(core->hw, req);
+	} else if (core->ops->round_rate) {
+		rate = core->ops->round_rate(core->hw, req->rate,
+					     &req->best_parent_rate);
+		if (rate < 0)
+			return rate;
 
-	if (!core)
-		return 0;
+		req->rate = rate;
+	} else {
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static void clk_core_init_rate_req(struct clk_core *core,
+				   struct clk_rate_request *req)
+{
+	struct clk_core *parent;
+
+	if (WARN_ON(!core || !req))
+		return;
 
 	parent = core->parent;
 	if (parent) {
@@ -852,22 +870,24 @@ static int clk_core_round_rate_nolock(struct clk_core *core,
 		req->best_parent_hw = NULL;
 		req->best_parent_rate = 0;
 	}
+}
 
-	if (core->ops->determine_rate) {
-		return core->ops->determine_rate(core->hw, req);
-	} else if (core->ops->round_rate) {
-		rate = core->ops->round_rate(core->hw, req->rate,
-					     &req->best_parent_rate);
-		if (rate < 0)
-			return rate;
+static int clk_core_round_rate_nolock(struct clk_core *core,
+				      struct clk_rate_request *req)
+{
+	lockdep_assert_held(&prepare_lock);
 
-		req->rate = rate;
-	} else if (core->flags & CLK_SET_RATE_PARENT) {
-		return clk_core_round_rate_nolock(parent, req);
-	} else {
-		req->rate = core->rate;
-	}
+	if (!core)
+		return 0;
+
+	clk_core_init_rate_req(core, req);
+
+	if (core->ops->determine_rate || core->ops->round_rate)
+		return clk_core_determine_round(core, req);
+	else if (core->flags & CLK_SET_RATE_PARENT)
+		return clk_core_round_rate_nolock(core->parent, req);
 
+	req->rate = core->rate;
 	return 0;
 }
 
@@ -1356,36 +1376,26 @@ static struct clk_core *clk_calc_new_rates(struct clk_core *core,
 	clk_core_get_boundaries(core, &min_rate, &max_rate);
 
 	/* find the closest rate and parent clk/rate */
-	if (core->ops->determine_rate) {
+	if (core->ops->determine_rate || core->ops->round_rate) {
 		struct clk_rate_request req;
 
 		req.rate = rate;
 		req.min_rate = min_rate;
 		req.max_rate = max_rate;
-		if (parent) {
-			req.best_parent_hw = parent->hw;
-			req.best_parent_rate = parent->rate;
-		} else {
-			req.best_parent_hw = NULL;
-			req.best_parent_rate = 0;
-		}
 
-		ret = core->ops->determine_rate(core->hw, &req);
+		clk_core_init_rate_req(core, &req);
+
+		ret = clk_core_determine_round(core, &req);
 		if (ret < 0)
 			return NULL;
 
 		best_parent_rate = req.best_parent_rate;
 		new_rate = req.rate;
 		parent = req.best_parent_hw ? req.best_parent_hw->core : NULL;
-	} else if (core->ops->round_rate) {
-		ret = core->ops->round_rate(core->hw, rate,
-					    &best_parent_rate);
-		if (ret < 0)
-			return NULL;
 
-		new_rate = ret;
 		if (new_rate < min_rate || new_rate > max_rate)
 			return NULL;
+
 	} else if (!parent || !(core->flags & CLK_SET_RATE_PARENT)) {
 		/* pass-through clock without adjustable parent */
 		core->new_rate = core->rate;
-- 
2.9.4

[PATCH 04/10] clk: add support for clock protection

[Jerome Brunet]

The patch adds clk_protect and clk_unprotect to the CCF API. These
functions allow a consumer to inform the system that the rate of clock is
critical to for its operations and it can't tolerate other consumers
changing the rate or introducing glitches while the clock is protected.

Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
---
 drivers/clk/clk.c            | 198 +++++++++++++++++++++++++++++++++++++++++--
 include/linux/clk-provider.h |   1 +
 include/linux/clk.h          |  29 +++++++
 3 files changed, 221 insertions(+), 7 deletions(-)

diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index 100f72472e10..9c15319bc454 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -60,6 +60,7 @@ struct clk_core {
 	bool			orphan;
 	unsigned int		enable_count;
 	unsigned int		prepare_count;
+	unsigned int		protect_count;
 	unsigned long		min_rate;
 	unsigned long		max_rate;
 	unsigned long		accuracy;
@@ -84,6 +85,7 @@ struct clk {
 	const char *con_id;
 	unsigned long min_rate;
 	unsigned long max_rate;
+	unsigned long protect_count;
 	struct hlist_node clks_node;
 };
 
@@ -160,6 +162,11 @@ static bool clk_core_is_prepared(struct clk_core *core)
 	return core->ops->is_prepared(core->hw);
 }
 
+static bool clk_core_rate_is_protected(struct clk_core *core)
+{
+	return core->protect_count;
+}
+
 static bool clk_core_is_enabled(struct clk_core *core)
 {
 	/*
@@ -328,6 +335,11 @@ bool clk_hw_is_prepared(const struct clk_hw *hw)
 	return clk_core_is_prepared(hw->core);
 }
 
+bool clk_hw_rate_is_protected(const struct clk_hw *hw)
+{
+	return clk_core_rate_is_protected(hw->core);
+}
+
 bool clk_hw_is_enabled(const struct clk_hw *hw)
 {
 	return clk_core_is_enabled(hw->core);
@@ -584,6 +596,102 @@ int clk_prepare(struct clk *clk)
 }
 EXPORT_SYMBOL_GPL(clk_prepare);
 
+static void clk_core_rate_unprotect(struct clk_core *core)
+{
+	lockdep_assert_held(&prepare_lock);
+
+	if (!core)
+		return;
+
+	if (WARN_ON(core->protect_count == 0))
+		return;
+
+	if (--core->protect_count > 0)
+		return;
+
+	clk_core_rate_unprotect(core->parent);
+}
+
+/**
+ * clk_rate_unprotect - unprotect the rate of a clock source
+ * @clk: the clk being unprotected
+ *
+ * clk_unprotect completes a critical section during which the clock
+ * consumer cannot tolerate any change to the clock rate. If no other clock
+ * consumers have protected clocks in the parent chain, then calls to this
+ * function will allow the clocks in the parent chain to change rates
+ * freely.
+ *
+ * Unlike the clk_set_rate_range method, which allows the rate to change
+ * within a given range, protected clocks cannot have their rate changed,
+ * either directly or indirectly due to changes further up the parent chain
+ * of clocks.
+ *
+ * Calls to clk_unprotect must be balanced with calls to clk_protect. Calls
+ * to this function may sleep, and do not return error status.
+ */
+void clk_rate_unprotect(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->protect_count <= 0))
+		goto out;
+
+	clk_core_rate_unprotect(clk->core);
+	clk->protect_count--;
+out:
+	clk_prepare_unlock();
+}
+EXPORT_SYMBOL_GPL(clk_rate_unprotect);
+
+static void clk_core_rate_protect(struct clk_core *core)
+{
+	lockdep_assert_held(&prepare_lock);
+
+	if (!core)
+		return;
+
+	if (core->protect_count == 0)
+		clk_core_rate_protect(core->parent);
+
+	core->protect_count++;
+}
+
+/**
+ * clk_rate_protect - protect a clock source
+ * @clk: the clk being protected
+ *
+ * clk_protect begins a critical section during which the clock consumer
+ * cannot tolerate any change to the clock rate. This results in all clocks
+ * up the parent chain to also be rate-protected.
+ *
+ * Unlike the clk_set_rate_range method, which allows the rate to change
+ * within a given range, protected clocks cannot have their rate changed,
+ * either directly or indirectly due to changes further up the parent chain
+ * of clocks.
+ *
+ * Calls to clk_protect should be balanced with calls to clk_unprotect.
+ * Calls to this function may sleep, and do not return error status.
+ */
+void clk_rate_protect(struct clk *clk)
+{
+	if (!clk)
+		return;
+
+	clk_prepare_lock();
+	clk_core_rate_protect(clk->core);
+	clk->protect_count++;
+	clk_prepare_unlock();
+}
+EXPORT_SYMBOL_GPL(clk_rate_protect);
+
 static void clk_core_disable(struct clk_core *core)
 {
 	lockdep_assert_held(&enable_lock);
@@ -838,7 +946,15 @@ static int clk_core_determine_round(struct clk_core *core,
 {
 	long rate;
 
-	if (core->ops->determine_rate) {
+	/*
+	 * 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 protecting the
+	 *   provider (and only once)
+	 */
+	if (clk_core_rate_is_protected(core)) {
+		req->rate = core->rate;
+	} else if (core->ops->determine_rate) {
 		return core->ops->determine_rate(core->hw, req);
 	} else if (core->ops->round_rate) {
 		rate = core->ops->round_rate(core->hw, req->rate,
@@ -944,10 +1060,17 @@ long clk_round_rate(struct clk *clk, unsigned long rate)
 
 	clk_prepare_lock();
 
+	if (clk->protect_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->protect_count)
+		clk_core_rate_protect(clk->core);
+
 	clk_prepare_unlock();
 
 	if (ret)
@@ -1583,6 +1706,10 @@ static int clk_core_set_rate_nolock(struct clk_core *core,
 	if (rate == clk_core_get_rate_nolock(core))
 		return 0;
 
+	/* fail on a direct rate set of a protected provider */
+	if (clk_core_rate_is_protected(core))
+		return -EBUSY;
+
 	if ((core->flags & CLK_SET_RATE_GATE) && core->prepare_count)
 		return -EBUSY;
 
@@ -1639,8 +1766,14 @@ int clk_set_rate(struct clk *clk, unsigned long rate)
 	/* prevent racing with updates to the clock topology */
 	clk_prepare_lock();
 
+	if (clk->protect_count)
+		clk_core_rate_unprotect(clk->core);
+
 	ret = clk_core_set_rate_nolock(clk->core, rate);
 
+	if (clk->protect_count)
+		clk_core_rate_protect(clk->core);
+
 	clk_prepare_unlock();
 
 	return ret;
@@ -1671,12 +1804,18 @@ int clk_set_rate_range(struct clk *clk, unsigned long min, unsigned long max)
 
 	clk_prepare_lock();
 
+	if (clk->protect_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->protect_count)
+		clk_core_rate_protect(clk->core);
+
 	clk_prepare_unlock();
 
 	return ret;
@@ -1818,6 +1957,9 @@ static int clk_core_set_parent_nolock(struct clk_core *core,
 	if ((core->flags & CLK_SET_PARENT_GATE) && core->prepare_count)
 		return -EBUSY;
 
+	if (clk_core_rate_is_protected(core))
+		return -EBUSY;
+
 	/* try finding the new parent index */
 	if (parent) {
 		p_index = clk_fetch_parent_index(core, parent);
@@ -1875,8 +2017,16 @@ int clk_set_parent(struct clk *clk, struct clk *parent)
 		return 0;
 
 	clk_prepare_lock();
+
+	if (clk->protect_count)
+		clk_core_rate_unprotect(clk->core);
+
 	ret = clk_core_set_parent_nolock(clk->core,
 					 parent ? parent->core : NULL);
+
+	if (clk->protect_count)
+		clk_core_rate_protect(clk->core);
+
 	clk_prepare_unlock();
 
 	return ret;
@@ -1890,7 +2040,10 @@ static int clk_core_set_phase_nolock(struct clk_core *core, int degrees)
 	if (!core)
 		return 0;
 
-	trace_clk_set_phase(clk->core, degrees);
+	if (clk_core_rate_is_protected(core))
+		return -EBUSY;
+
+	trace_clk_set_phase(core, degrees);
 
 	if (core->ops->set_phase)
 		ret = core->ops->set_phase(core->hw, degrees);
@@ -1933,7 +2086,15 @@ int clk_set_phase(struct clk *clk, int degrees)
 		degrees += 360;
 
 	clk_prepare_lock();
+
+	if (clk->protect_count)
+		clk_core_rate_unprotect(clk->core);
+
 	ret = clk_core_set_phase_nolock(clk->core, degrees);
+
+	if (clk->protect_count)
+		clk_core_rate_protect(clk->core);
+
 	clk_prepare_unlock();
 
 	return ret;
@@ -2020,11 +2181,12 @@ static void clk_summary_show_one(struct seq_file *s, struct clk_core *c,
 	if (!c)
 		return;
 
-	seq_printf(s, "%*s%-*s %11d %12d %11lu %10lu %-3d\n",
+	seq_printf(s, "%*s%-*s %11d %12d %12d %11lu %10lu %-3d\n",
 		   level * 3 + 1, "",
 		   30 - level * 3, c->name,
-		   c->enable_count, c->prepare_count, clk_core_get_rate(c),
-		   clk_core_get_accuracy(c), clk_core_get_phase(c));
+		   c->enable_count, c->prepare_count, c->protect_count,
+		   clk_core_get_rate(c), clk_core_get_accuracy(c),
+		   clk_core_get_phase(c));
 }
 
 static void clk_summary_show_subtree(struct seq_file *s, struct clk_core *c,
@@ -2046,8 +2208,8 @@ static int clk_summary_show(struct seq_file *s, void *data)
 	struct clk_core *c;
 	struct hlist_head **lists = (struct hlist_head **)s->private;
 
-	seq_puts(s, "   clock                         enable_cnt  prepare_cnt        rate   accuracy   phase\n");
-	seq_puts(s, "----------------------------------------------------------------------------------------\n");
+	seq_puts(s, "   clock                         enable_cnt  prepare_cnt  protect_cnt        rate   accuracy   phase\n");
+	seq_puts(s, "----------------------------------------------------------------------------------------------------\n");
 
 	clk_prepare_lock();
 
@@ -2082,6 +2244,7 @@ static void clk_dump_one(struct seq_file *s, struct clk_core *c, int level)
 	seq_printf(s, "\"%s\": { ", c->name);
 	seq_printf(s, "\"enable_count\": %d,", c->enable_count);
 	seq_printf(s, "\"prepare_count\": %d,", c->prepare_count);
+	seq_printf(s, "\"protect_count\": %d,", c->protect_count);
 	seq_printf(s, "\"rate\": %lu,", clk_core_get_rate(c));
 	seq_printf(s, "\"accuracy\": %lu,", clk_core_get_accuracy(c));
 	seq_printf(s, "\"phase\": %d", clk_core_get_phase(c));
@@ -2212,6 +2375,11 @@ static int clk_debug_create_one(struct clk_core *core, struct dentry *pdentry)
 	if (!d)
 		goto err_out;
 
+	d = debugfs_create_u32("clk_protect_count", S_IRUGO, core->dentry,
+			(u32 *)&core->protect_count);
+	if (!d)
+		goto err_out;
+
 	d = debugfs_create_u32("clk_notifier_count", S_IRUGO, core->dentry,
 			(u32 *)&core->notifier_count);
 	if (!d)
@@ -2775,6 +2943,11 @@ void clk_unregister(struct clk *clk)
 	if (clk->core->prepare_count)
 		pr_warn("%s: unregistering prepared clock: %s\n",
 					__func__, clk->core->name);
+
+	if (clk->core->protect_count)
+		pr_warn("%s: unregistering protected clock: %s\n",
+					__func__, clk->core->name);
+
 	kref_put(&clk->core->ref, __clk_release);
 unlock:
 	clk_prepare_unlock();
@@ -2933,6 +3106,17 @@ void __clk_put(struct clk *clk)
 
 	clk_prepare_lock();
 
+	/*
+	 * Before calling clk_put, all calls to clk_rate_protect from a given
+	 * user must be balanced with calls to clk_rate_unprotect and by that
+	 * same user
+	 */
+	WARN_ON(clk->protect_count);
+
+	/* We voiced our concern, let's sanitize the situation */
+	for (; clk->protect_count; clk->protect_count--)
+		clk_core_rate_unprotect(clk->core);
+
 	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-provider.h b/include/linux/clk-provider.h
index a428aec36ace..ebd7df5f375f 100644
--- a/include/linux/clk-provider.h
+++ b/include/linux/clk-provider.h
@@ -739,6 +739,7 @@ unsigned long clk_hw_get_rate(const struct clk_hw *hw);
 unsigned long __clk_get_flags(struct clk *clk);
 unsigned long clk_hw_get_flags(const struct clk_hw *hw);
 bool clk_hw_is_prepared(const struct clk_hw *hw);
+bool clk_hw_rate_is_protected(const struct clk_hw *hw);
 bool clk_hw_is_enabled(const struct clk_hw *hw);
 bool __clk_is_enabled(struct clk *clk);
 struct clk *__clk_lookup(const char *name);
diff --git a/include/linux/clk.h b/include/linux/clk.h
index 024cd07870d0..85d73e02df40 100644
--- a/include/linux/clk.h
+++ b/include/linux/clk.h
@@ -265,6 +265,30 @@ 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_protect - inform the system when the clock rate must be protected.
+ * @clk: clock source
+ *
+ * This function informs the system that the consumer protecting the clock
+ * depends on the rate of the clock source and can't tolerate any glitches
+ * introduced by further clock rate change or re-parenting of the clock source.
+ *
+ * Must not be called from within atomic context.
+ */
+void clk_rate_protect(struct clk *clk);
+
+/**
+ * clk_rate_unprotect - release the protection of the clock source.
+ * @clk: clock source
+ *
+ * This function informs the system that the consumer previously protecting the
+ * clock rate can now deal with other consumer altering the clock source rate
+ *
+ * The caller must balance the number of rate_protect and rate_unprotect calls.
+ *
+ * Must not be called from within atomic context.
+ */
+void clk_rate_unprotect(struct clk *clk);
 
 /**
  * clk_enable - inform the system when the clock source should be running.
@@ -460,6 +484,11 @@ static inline void clk_put(struct clk *clk) {}
 
 static inline void devm_clk_put(struct device *dev, struct clk *clk) {}
 
+
+static inline void clk_protect(struct clk *clk) {}
+
+static inline void clk_unprotect(struct clk *clk) {}
+
 static inline int clk_enable(struct clk *clk)
 {
 	return 0;
-- 
2.9.4

[PATCH 05/10] clk: add clk_set_rate_protect

[Jerome Brunet]

clk_set_rate_protect is a combination of clk_set_rate and clk_rate_protect
within a critical section. In case where several protecting consumers
compete to set the rate of the same provider, it provides a way to make
sure that at least one of them will be satisfied before the resource is
locked.

This is to avoid the unlikely situation where several consumers protect a
clock provider and none actually get a rate it can work with.

Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
---
 drivers/clk/clk.c   | 45 +++++++++++++++++++++++++++++++++++++++++++++
 include/linux/clk.h | 14 ++++++++++++++
 2 files changed, 59 insertions(+)

diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index 9c15319bc454..132eb1a2938f 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -1781,6 +1781,51 @@ int clk_set_rate(struct clk *clk, unsigned long rate)
 EXPORT_SYMBOL_GPL(clk_set_rate);
 
 /**
+ * clk_set_rate_protect - specify a new rate and protect it
+ * @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_protect within
+ * a critical section
+ *
+ * This can be used initially to ensure that at least 1 consumers is
+ * statisfied when several protecting consummers are competing for the
+ * same clock provider.
+ *
+ * The protection is not applied if setting the rate failed.
+ *
+ * Returns 0 on success, -EERROR otherwise.
+ */
+int clk_set_rate_protect(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 in 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->protect_count++;
+	}
+
+	clk_prepare_unlock();
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(clk_set_rate_protect);
+
+/**
  * clk_set_rate_range - set a rate range for a clock source
  * @clk: clock source
  * @min: desired minimum clock rate in Hz, inclusive
diff --git a/include/linux/clk.h b/include/linux/clk.h
index 85d73e02df40..d3c299d23ae7 100644
--- a/include/linux/clk.h
+++ b/include/linux/clk.h
@@ -388,6 +388,15 @@ long clk_round_rate(struct clk *clk, unsigned long rate);
 int clk_set_rate(struct clk *clk, unsigned long rate);
 
 /**
+ * clk_set_rate_protect - set and protect the clock rate for a clock source
+ * @clk: clock source
+ * @rate: desired clock rate in Hz
+ *
+ * Returns success (0) or negative errno.
+ */
+int clk_set_rate_protect(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
@@ -506,6 +515,11 @@ static inline int clk_set_rate(struct clk *clk, unsigned long rate)
 	return 0;
 }
 
+static inline int clk_set_rate_protect(struct clk *clk, unsigned long rate)
+{
+	return 0;
+}
+
 static inline long clk_round_rate(struct clk *clk, unsigned long rate)
 {
 	return 0;
-- 
2.9.4

[PATCH 07/10] clk: cosmetic changes to clk_summary debugfs entry

[Jerome Brunet]

clk_summary debugfs entry was already well over the traditional 80
characters per line limit but it grew even larger with the addition of
clock protection.

Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
---
 drivers/clk/clk.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index d61218d1f41e..e60d86d7c082 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -2234,7 +2234,7 @@ static void clk_summary_show_one(struct seq_file *s, struct clk_core *c,
 	if (!c)
 		return;
 
-	seq_printf(s, "%*s%-*s %11d %12d %12d %11lu %10lu %-3d\n",
+	seq_printf(s, "%*s%-*s %7d %8d %8d %11lu %10lu %-3d\n",
 		   level * 3 + 1, "",
 		   30 - level * 3, c->name,
 		   c->enable_count, c->prepare_count, c->protect_count,
@@ -2261,8 +2261,9 @@ static int clk_summary_show(struct seq_file *s, void *data)
 	struct clk_core *c;
 	struct hlist_head **lists = (struct hlist_head **)s->private;
 
-	seq_puts(s, "   clock                         enable_cnt  prepare_cnt  protect_cnt        rate   accuracy   phase\n");
-	seq_puts(s, "----------------------------------------------------------------------------------------------------\n");
+	seq_puts(s, "                                 enable  prepare  protect                               \n");
+	seq_puts(s, "   clock                          count    count    count        rate   accuracy   phase\n");
+	seq_puts(s, "----------------------------------------------------------------------------------------\n");
 
 	clk_prepare_lock();
 
-- 
2.9.4

[PATCH 08/10] clk: fix incorrect usage of ENOSYS

[Jerome Brunet]

ENOSYS is special and should only be used for incorrect syscall number.
It does not seem to be the case here.

Reported by checkpatch.pl while working on clock protection.

Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
---
 drivers/clk/clk.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index e60d86d7c082..5980080a86c0 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -2004,7 +2004,7 @@ static int clk_core_set_parent_nolock(struct clk_core *core,
 
 	/* verify ops for for multi-parent clks */
 	if ((core->num_parents > 1) && (!core->ops->set_parent))
-		return -ENOSYS;
+		return -EPERM;
 
 	/* check that we are allowed to re-parent if the clock is in use */
 	if ((core->flags & CLK_SET_PARENT_GATE) && core->prepare_count)
-- 
2.9.4

[PATCH 09/10] clk: fix CLK_SET_RATE_GATE with clock rate protection

[Jerome Brunet]

Using clock rate protection, we can now enforce CLK_SET_RATE_GATE along the
clock tree

Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
---
 drivers/clk/clk.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index 5980080a86c0..1db3ad28dd85 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -491,6 +491,9 @@ static void clk_core_unprepare(struct clk_core *core)
 	if (WARN_ON(core->prepare_count == 1 && core->flags & CLK_IS_CRITICAL))
 		return;
 
+	if (core->flags & CLK_SET_RATE_GATE)
+		clk_core_rate_unprotect(core);
+
 	if (--core->prepare_count > 0)
 		return;
 
@@ -561,6 +564,14 @@ static int clk_core_prepare(struct clk_core *core)
 
 	core->prepare_count++;
 
+	/*
+	 * CLK_SET_RATE_GATE is a special case of clock protection
+	 * Instead of a consumer protection, the provider is protecting
+	 * itself when prepared
+	 */
+	if (core->flags & CLK_SET_RATE_GATE)
+		clk_core_rate_protect(core);
+
 	return 0;
 }
 
@@ -1710,9 +1721,6 @@ static int clk_core_set_rate_nolock(struct clk_core *core,
 	if (clk_core_rate_is_protected(core))
 		return -EBUSY;
 
-	if ((core->flags & CLK_SET_RATE_GATE) && core->prepare_count)
-		return -EBUSY;
-
 	/* calculate new rates and get the topmost changed clock */
 	top = clk_calc_new_rates(core, rate);
 	if (!top)
-- 
2.9.4

[PATCH 10/10] clk: move CLK_SET_RATE_GATE protection from prepare to enable

[Jerome Brunet]

CLK_SET_RATE_GATE name suggest that the rate can be set when the provider
is gated (disabled). With the current implementation, the rate can only be
set when the provider is unprepared, while it should be allowed to set a
prepared and disable provider.
Fix this by moving the rate protection mechanism in the enable/disable
core functions

Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
---
 drivers/clk/clk.c | 23 ++++++++++++-----------
 1 file changed, 12 insertions(+), 11 deletions(-)

diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index 1db3ad28dd85..3e2eb21ca8cd 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -491,9 +491,6 @@ static void clk_core_unprepare(struct clk_core *core)
 	if (WARN_ON(core->prepare_count == 1 && core->flags & CLK_IS_CRITICAL))
 		return;
 
-	if (core->flags & CLK_SET_RATE_GATE)
-		clk_core_rate_unprotect(core);
-
 	if (--core->prepare_count > 0)
 		return;
 
@@ -564,14 +561,6 @@ static int clk_core_prepare(struct clk_core *core)
 
 	core->prepare_count++;
 
-	/*
-	 * CLK_SET_RATE_GATE is a special case of clock protection
-	 * Instead of a consumer protection, the provider is protecting
-	 * itself when prepared
-	 */
-	if (core->flags & CLK_SET_RATE_GATE)
-		clk_core_rate_protect(core);
-
 	return 0;
 }
 
@@ -716,6 +705,9 @@ static void clk_core_disable(struct clk_core *core)
 	if (WARN_ON(core->enable_count == 1 && core->flags & CLK_IS_CRITICAL))
 		return;
 
+	if (core->flags & CLK_SET_RATE_GATE)
+		clk_core_rate_unprotect(core);
+
 	if (--core->enable_count > 0)
 		return;
 
@@ -791,6 +783,15 @@ static int clk_core_enable(struct clk_core *core)
 	}
 
 	core->enable_count++;
+
+	/*
+	 * CLK_SET_RATE_GATE is a special case of clock protection
+	 * Instead of a consumer protection, the provider is protecting
+	 * itself when enabled
+	 */
+	if (core->flags & CLK_SET_RATE_GATE)
+		clk_core_rate_protect(core);
+
 	return 0;
 }
 
-- 
2.9.4

[PATCH 00/10] clk: implement clock rate protection mechanism

[Jerome Brunet]

On Thu, 2017-05-18 at 18:37 +0200, Jerome Brunet wrote:
> This Patchset is related the RFC [0] and the discussion around
> CLK_SET_RATE_GATE available here [1]
> 
> The goal of this patchset is to provide a way for consumers to inform the
> system that they depend on the rate of the clock source and can't tolerate
> other consumers changing the rate or causing glitches.
> 
> 

Stephen, Mike,

I've realized that a few more changes would improve set_rate changes handling.
Please ignore this series.

I'll send another one soon.

Cheers

Jerome