These new API calls will firstly provide a mechanisms to tag a clock as
critical and secondly allow any knowledgeable driver to (un)gate clocks,
even if they are marked as critical.

Suggested-by: Maxime Ripard <redacted>
Signed-off-by: Lee Jones <redacted>
---
 drivers/clk/clk.c            | 45 ++++++++++++++++++++++++++++++++++++++++++++
 include/linux/clk-provider.h |  2 ++
 include/linux/clk.h          | 30 +++++++++++++++++++++++++++++
 3 files changed, 77 insertions(+)

diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index 61c3fc5..486b1da 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c

@@ -46,6 +46,21 @@ static struct clk_core *clk_core_lookup(const char *name);
 
 /***    private data structures    ***/
 
+/**
+ * struct critical -   Provides 'play' over critical clocks.  A clock can be
+ *                     marked as critical, meaning that it should not be
+ *                     disabled.  However, if a driver which is aware of the
+ *                     critical behaviour wants to control it, it can do so
+ *                     using clk_enable_critical() and clk_disable_critical().
+ *
+ * @enabled    Is clock critical?  Once set, doesn't change
+ * @leave_on   Self explanatory.  Can be disabled by knowledgeable drivers

+ */
+struct critical {
+       bool enabled;
+       bool leave_on;
+};
+
 struct clk_core {
        const char              *name;
        const struct clk_ops    *ops;

@@ -75,6 +90,7 @@ struct clk_core {
        struct dentry           *dentry;
 #endif
        struct kref             ref;
+       struct critical         critical;
 };
 
 struct clk {

@@ -995,6 +1011,10 @@ static void clk_core_disable(struct clk_core *clk)
        if (WARN_ON(clk->enable_count == 0))
                return;
 
+       /* Refuse to turn off a critical clock */
+       if (clk->enable_count == 1 && clk->critical.leave_on)
+               return;

+
        if (--clk->enable_count > 0)
                return;
 

@@ -1037,6 +1057,13 @@ void clk_disable(struct clk *clk)
 }
 EXPORT_SYMBOL_GPL(clk_disable);
 
+void clk_disable_critical(struct clk *clk)
+{
+       clk->core->critical.leave_on = false;
+       clk_disable(clk);
+}
+EXPORT_SYMBOL_GPL(clk_disable_critical);
+
 static int clk_core_enable(struct clk_core *clk)
 {
        int ret = 0;

@@ -1100,6 +1127,15 @@ int clk_enable(struct clk *clk)
 }
 EXPORT_SYMBOL_GPL(clk_enable);
 
+int clk_enable_critical(struct clk *clk)
+{
+       if (clk->core->critical.enabled)
+               clk->core->critical.leave_on = true;
+
+       return clk_enable(clk);
+}
+EXPORT_SYMBOL_GPL(clk_enable_critical);
+
 static unsigned long clk_core_round_rate_nolock(struct clk_core *clk,
                                                unsigned long rate,
                                                unsigned long min_rate,

@@ -2482,6 +2518,15 @@ fail_out:
 }
 EXPORT_SYMBOL_GPL(clk_register);
 
+void clk_init_critical(struct clk *clk)
+{
+       struct critical *critical = &clk->core->critical;
+
+       critical->enabled = true;
+       critical->leave_on = true;
+}
+EXPORT_SYMBOL_GPL(clk_init_critical);
+
 /*
  * Free memory allocated for a clock.
  * Caller must hold prepare_lock.

diff --git a/include/linux/clk-provider.h b/include/linux/clk-provider.h
index 5591ea7..15ef8c9 100644
--- a/include/linux/clk-provider.h
+++ b/include/linux/clk-provider.h

@@ -563,6 +563,8 @@ struct clk *devm_clk_register(struct device *dev, struct clk_hw *hw);
 void clk_unregister(struct clk *clk);
 void devm_clk_unregister(struct device *dev, struct clk *clk);
 
+void clk_init_critical(struct clk *clk);
+
 /* helper functions */
 const char *__clk_get_name(struct clk *clk);
 struct clk_hw *__clk_get_hw(struct clk *clk);

diff --git a/include/linux/clk.h b/include/linux/clk.h
index 8381bbf..9807f3b 100644
--- a/include/linux/clk.h
+++ b/include/linux/clk.h

@@ -231,6 +231,19 @@ struct clk *devm_clk_get(struct device *dev, const char *id);
 int clk_enable(struct clk *clk);
 
 /**
+ * clk_enable_critical - inform the system when the clock source should be
+ *                      running, even if clock is critical.
+ * @clk: clock source
+ *
+ * If the clock can not be enabled/disabled, this should return success.
+ *
+ * May be called from atomic contexts.
+ *
+ * Returns success (0) or negative errno.
+ */
+int clk_enable_critical(struct clk *clk);
+
+/**
  * clk_disable - inform the system when the clock source is no longer required.
  * @clk: clock source
  *

@@ -247,6 +260,23 @@ int clk_enable(struct clk *clk);
 void clk_disable(struct clk *clk);
 
 /**
+ * clk_disable_critical - inform the system when the clock source is no
+ *                       longer required, even if clock is critical.
+ * @clk: clock source
+ *
+ * Inform the system that a clock source is no longer required by
+ * a driver and may be shut down.
+ *
+ * May be called from atomic contexts.
+ *
+ * Implementation detail: if the clock source is shared between
+ * multiple drivers, clk_enable_critical() calls must be balanced
+ * by the same number of clk_disable_critical() calls for the clock
+ * source to be disabled.
+ */
+void clk_disable_critical(struct clk *clk);
+
+/**
  * clk_get_rate - obtain the current clock rate (in Hz) for a clock source.
  *               This is only valid once the clock source has been enabled.
  * @clk: clock source

-- 
1.9.1