[PATCH v3 0/5] clk: clock deregistration support

[PATCH v3 0/5] clk: clock deregistration support

[Sylwester Nawrocki]

This patch set is intended to add clock deregistration support to
the common clock framework, required for clock suppliers as loadable
modules.  Previous version of this series can be found at [1].

Changes since v2:
 - reordered the patches so the race condition is fixed before it can
   actually cause any issues,
 - fixed handling of NULL clock pointers in __clk_get(), __clk_put(),
 - added patch adding actual asignment of clk->owner; more details are
   discussed in that specific patch.

Changes since v1:
 - moved of_clk_{lock, unlock}, __of_clk_get_from_provider() function
   declaractions to a local header,
 - renamed clk_dummy_* to clk_nodrv_*.


[1] http://www.spinics.net/lists/linux-sh/msg22948.html

Sylwester Nawrocki (5):
  clk: Provide not locked variant of of_clk_get_from_provider()
  clkdev: Fix race condition in clock lookup from device tree
  clk: Add common __clk_get(), __clk_put() implementations
  clk: Assign module owner of a clock being registered
  clk: Implement clk_unregister

 arch/arm/include/asm/clkdev.h      |    2 +
 arch/blackfin/include/asm/clkdev.h |    2 +
 arch/mips/include/asm/clkdev.h     |    2 +
 arch/sh/include/asm/clkdev.h       |    2 +
 drivers/clk/clk.c                  |  189 +++++++++++++++++++++++++++++++++---
 drivers/clk/clk.h                  |   16 +++
 drivers/clk/clkdev.c               |   12 ++-
 include/linux/clk-private.h        |    5 +
 include/linux/clk-provider.h       |    2 +
 include/linux/clkdev.h             |    5 +
 10 files changed, 224 insertions(+), 13 deletions(-)
 create mode 100644 drivers/clk/clk.h

--
1.7.9.5

[PATCH v3 1/5] clk: Provide not locked variant of of_clk_get_from_provider()

[Sylwester Nawrocki]

Add helper functions for the of_clk_providers list locking and
an unlocked variant of of_clk_get_from_provider().
These functions are intended to be used in the clkdev to avoid
race condition in the device tree based clock look up in clk_get().

Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Acked-by: Russell King <rmk+kernel@arm.linux.org.uk>
---
Changes since v2:
 - fixed typo in clk.h.

Changes since v1:
 - moved the function declaractions to a local header.
---
 drivers/clk/clk.c |   38 ++++++++++++++++++++++++++++++--------
 drivers/clk/clk.h |   16 ++++++++++++++++
 2 files changed, 46 insertions(+), 8 deletions(-)
 create mode 100644 drivers/clk/clk.h

diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index 54a191c..eb3207e 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -21,6 +21,8 @@
 #include <linux/init.h>
 #include <linux/sched.h>
 
+#include "clk.h"
+
 static DEFINE_SPINLOCK(enable_lock);
 static DEFINE_MUTEX(prepare_lock);
 
@@ -1990,7 +1992,18 @@ static const struct of_device_id __clk_of_table_sentinel
 	__used __section(__clk_of_table_end);
 
 static LIST_HEAD(of_clk_providers);
-static DEFINE_MUTEX(of_clk_lock);
+static DEFINE_MUTEX(of_clk_mutex);
+
+/* of_clk_provider list locking helpers */
+void of_clk_lock(void)
+{
+	mutex_lock(&of_clk_mutex);
+}
+
+void of_clk_unlock(void)
+{
+	mutex_unlock(&of_clk_mutex);
+}
 
 struct clk *of_clk_src_simple_get(struct of_phandle_args *clkspec,
 				     void *data)
@@ -2034,9 +2047,9 @@ int of_clk_add_provider(struct device_node *np,
 	cp->data = data;
 	cp->get = clk_src_get;
 
-	mutex_lock(&of_clk_lock);
+	mutex_lock(&of_clk_mutex);
 	list_add(&cp->link, &of_clk_providers);
-	mutex_unlock(&of_clk_lock);
+	mutex_unlock(&of_clk_mutex);
 	pr_debug("Added clock from %s\n", np->full_name);
 
 	return 0;
@@ -2051,7 +2064,7 @@ void of_clk_del_provider(struct device_node *np)
 {
 	struct of_clk_provider *cp;
 
-	mutex_lock(&of_clk_lock);
+	mutex_lock(&of_clk_mutex);
 	list_for_each_entry(cp, &of_clk_providers, link) {
 		if (cp->node == np) {
 			list_del(&cp->link);
@@ -2060,24 +2073,33 @@ void of_clk_del_provider(struct device_node *np)
 			break;
 		}
 	}
-	mutex_unlock(&of_clk_lock);
+	mutex_unlock(&of_clk_mutex);
 }
 EXPORT_SYMBOL_GPL(of_clk_del_provider);
 
-struct clk *of_clk_get_from_provider(struct of_phandle_args *clkspec)
+struct clk *__of_clk_get_from_provider(struct of_phandle_args *clkspec)
 {
 	struct of_clk_provider *provider;
 	struct clk *clk = ERR_PTR(-ENOENT);
 
 	/* Check if we have such a provider in our array */
-	mutex_lock(&of_clk_lock);
 	list_for_each_entry(provider, &of_clk_providers, link) {
 		if (provider->node == clkspec->np)
 			clk = provider->get(clkspec, provider->data);
 		if (!IS_ERR(clk))
 			break;
 	}
-	mutex_unlock(&of_clk_lock);
+
+	return clk;
+}
+
+struct clk *of_clk_get_from_provider(struct of_phandle_args *clkspec)
+{
+	struct clk *clk;
+
+	mutex_lock(&of_clk_mutex);
+	clk = __of_clk_get_from_provider(clkspec);
+	mutex_unlock(&of_clk_mutex);
 
 	return clk;
 }
diff --git a/drivers/clk/clk.h b/drivers/clk/clk.h
new file mode 100644
index 0000000..795cc9f
--- /dev/null
+++ b/drivers/clk/clk.h
@@ -0,0 +1,16 @@
+/*
+ * linux/drivers/clk/clk.h
+ *
+ * Copyright (C) 2013 Samsung Electronics Co., Ltd.
+ * Sylwester Nawrocki <s.nawrocki@samsung.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#if defined(CONFIG_OF) && defined(CONFIG_COMMON_CLK)
+struct clk *__of_clk_get_from_provider(struct of_phandle_args *clkspec);
+void of_clk_lock(void);
+void of_clk_unlock(void);
+#endif
-- 
1.7.9.5

[PATCH v3 2/5] clkdev: Fix race condition in clock lookup from device tree

[Sylwester Nawrocki]

There is currently a race condition in the device tree part of clk_get()
function, since the pointer returned from of_clk_get_by_name() may become
invalid before __clk_get() call. I.e. due to the clock provider driver
remove() callback being called in between of_clk_get_by_name() and
__clk_get().

Fix this by doing both the look up and __clk_get() operations with the
clock providers list mutex held. This ensures that the clock pointer
returned from __of_clk_get_from_provider() call and passed to __clk_get()
is valid, as long as the clock supplier module first removes its clock
provider instance and then does clk_unregister() on the corresponding
clocks.

Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Acked-by: Russell King <rmk+kernel@arm.linux.org.uk>
---
Changes since v2:
 - none.

Changes since v1:
 - include "clk.h".
---
 drivers/clk/clkdev.c |   12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/clk/clkdev.c b/drivers/clk/clkdev.c
index 442a313..48f6721 100644
--- a/drivers/clk/clkdev.c
+++ b/drivers/clk/clkdev.c
@@ -21,6 +21,8 @@
 #include <linux/clkdev.h>
 #include <linux/of.h>
 
+#include "clk.h"
+
 static LIST_HEAD(clocks);
 static DEFINE_MUTEX(clocks_mutex);
 
@@ -39,7 +41,13 @@ struct clk *of_clk_get(struct device_node *np, int index)
 	if (rc)
 		return ERR_PTR(rc);
 
-	clk = of_clk_get_from_provider(&clkspec);
+	of_clk_lock();
+	clk = __of_clk_get_from_provider(&clkspec);
+
+	if (!IS_ERR(clk) && !__clk_get(clk))
+		clk = ERR_PTR(-ENOENT);
+
+	of_clk_unlock();
 	of_node_put(clkspec.np);
 	return clk;
 }
@@ -157,7 +165,7 @@ struct clk *clk_get(struct device *dev, const char *con_id)
 
 	if (dev) {
 		clk = of_clk_get_by_name(dev->of_node, con_id);
-		if (!IS_ERR(clk) && __clk_get(clk))
+		if (!IS_ERR(clk))
 			return clk;
 	}
 
-- 
1.7.9.5

[PATCH v3 2/5] clkdev: Fix race condition in clock lookup from device tree

[Sylwester Nawrocki]

On 08/23/2013 05:03 PM, Sylwester Nawrocki wrote:
> There is currently a race condition in the device tree part of clk_get()
> function, since the pointer returned from of_clk_get_by_name() may become
> invalid before __clk_get() call. I.e. due to the clock provider driver
> remove() callback being called in between of_clk_get_by_name() and
> __clk_get().
> 
> Fix this by doing both the look up and __clk_get() operations with the
> clock providers list mutex held. This ensures that the clock pointer
> returned from __of_clk_get_from_provider() call and passed to __clk_get()
> is valid, as long as the clock supplier module first removes its clock
> provider instance and then does clk_unregister() on the corresponding
> clocks.
> 
> Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
> Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>

Oops, I missed to add:

Reviewed-by: Mike Turquette <mturquette@linaro.org>

> Acked-by: Russell King <rmk+kernel@arm.linux.org.uk>

[PATCH v3 3/5] clk: Add common __clk_get(), __clk_put() implementations

[Sylwester Nawrocki]

This patch adds common __clk_get(), __clk_put() clkdev helpers which
replace their platform specific counterparts when the common clock
API is enabled.

The owner module pointer field is added to struct clk so a reference
to the clock supplier module can be taken by the clock consumers.

Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
---
Changes since v2:
 - fixed handling of NULL clock pointers in __clk_get(), __clk_put();
---
 arch/arm/include/asm/clkdev.h      |    2 ++
 arch/blackfin/include/asm/clkdev.h |    2 ++
 arch/mips/include/asm/clkdev.h     |    2 ++
 arch/sh/include/asm/clkdev.h       |    2 ++
 drivers/clk/clk.c                  |   22 ++++++++++++++++++++++
 include/linux/clk-private.h        |    3 +++
 include/linux/clk-provider.h       |    2 ++
 include/linux/clkdev.h             |    5 +++++
 8 files changed, 40 insertions(+)

diff --git a/arch/arm/include/asm/clkdev.h b/arch/arm/include/asm/clkdev.h
index 80751c1..4e8a4b2 100644
--- a/arch/arm/include/asm/clkdev.h
+++ b/arch/arm/include/asm/clkdev.h
@@ -14,12 +14,14 @@
 
 #include <linux/slab.h>
 
+#ifndef CONFIG_COMMON_CLK
 #ifdef CONFIG_HAVE_MACH_CLKDEV
 #include <mach/clkdev.h>
 #else
 #define __clk_get(clk)	({ 1; })
 #define __clk_put(clk)	do { } while (0)
 #endif
+#endif
 
 static inline struct clk_lookup_alloc *__clkdev_alloc(size_t size)
 {
diff --git a/arch/blackfin/include/asm/clkdev.h b/arch/blackfin/include/asm/clkdev.h
index 9053bed..7ac2436 100644
--- a/arch/blackfin/include/asm/clkdev.h
+++ b/arch/blackfin/include/asm/clkdev.h
@@ -8,7 +8,9 @@ static inline struct clk_lookup_alloc *__clkdev_alloc(size_t size)
 	return kzalloc(size, GFP_KERNEL);
 }
 
+#ifndef CONFIG_COMMON_CLK
 #define __clk_put(clk)
 #define __clk_get(clk) ({ 1; })
+#endif
 
 #endif
diff --git a/arch/mips/include/asm/clkdev.h b/arch/mips/include/asm/clkdev.h
index 2624754..1b3ad7b 100644
--- a/arch/mips/include/asm/clkdev.h
+++ b/arch/mips/include/asm/clkdev.h
@@ -14,8 +14,10 @@
 
 #include <linux/slab.h>
 
+#ifndef CONFIG_COMMON_CLK
 #define __clk_get(clk)	({ 1; })
 #define __clk_put(clk)	do { } while (0)
+#endif
 
 static inline struct clk_lookup_alloc *__clkdev_alloc(size_t size)
 {
diff --git a/arch/sh/include/asm/clkdev.h b/arch/sh/include/asm/clkdev.h
index 6ba9186..c419014 100644
--- a/arch/sh/include/asm/clkdev.h
+++ b/arch/sh/include/asm/clkdev.h
@@ -25,7 +25,9 @@ static inline struct clk_lookup_alloc *__clkdev_alloc(size_t size)
 		return kzalloc(size, GFP_KERNEL);
 }
 
+#ifndef CONFIG_COMMON_CLK
 #define __clk_put(clk)
 #define __clk_get(clk) ({ 1; })
+#endif
 
 #endif /* __CLKDEV_H__ */
diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index eb3207e..c173f30 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -1852,6 +1852,28 @@ void devm_clk_unregister(struct device *dev, struct clk *clk)
 }
 EXPORT_SYMBOL_GPL(devm_clk_unregister);
 
+/*
+ * clkdev helpers
+ */
+int __clk_get(struct clk *clk)
+{
+	if (clk && !try_module_get(clk->owner))
+		return 0;
+
+	return 1;
+}
+EXPORT_SYMBOL(__clk_get);
+
+void __clk_put(struct clk *clk)
+{
+	if (WARN_ON_ONCE(IS_ERR(clk)))
+		return;
+
+	if (clk)
+		module_put(clk->owner);
+}
+EXPORT_SYMBOL(__clk_put);
+
 /***        clk rate change notifiers        ***/
 
 /**
diff --git a/include/linux/clk-private.h b/include/linux/clk-private.h
index dd7adff..b7c0b58 100644
--- a/include/linux/clk-private.h
+++ b/include/linux/clk-private.h
@@ -25,10 +25,13 @@
 
 #ifdef CONFIG_COMMON_CLK
 
+struct module;
+
 struct clk {
 	const char		*name;
 	const struct clk_ops	*ops;
 	struct clk_hw		*hw;
+	struct module		*owner;
 	struct clk		*parent;
 	const char		**parent_names;
 	struct clk		**parents;
diff --git a/include/linux/clk-provider.h b/include/linux/clk-provider.h
index 1ec14a7..2c42fde 100644
--- a/include/linux/clk-provider.h
+++ b/include/linux/clk-provider.h
@@ -133,6 +133,8 @@ struct clk_ops {
 	void		(*init)(struct clk_hw *hw);
 };
 
+struct module;
+
 /**
  * struct clk_init_data - holds init data that's common to all clocks and is
  * shared between the clock provider and the common clock framework.
diff --git a/include/linux/clkdev.h b/include/linux/clkdev.h
index a6a6f60..94bad77 100644
--- a/include/linux/clkdev.h
+++ b/include/linux/clkdev.h
@@ -43,4 +43,9 @@ int clk_add_alias(const char *, const char *, char *, struct device *);
 int clk_register_clkdev(struct clk *, const char *, const char *, ...);
 int clk_register_clkdevs(struct clk *, struct clk_lookup *, size_t);
 
+#ifdef CONFIG_COMMON_CLK
+int __clk_get(struct clk *clk);
+void __clk_put(struct clk *clk);
+#endif
+
 #endif
-- 
1.7.9.5

[PATCH v3 3/5] clk: Add common __clk_get(), __clk_put() implementations

[Russell King - ARM Linux]

On Fri, Aug 23, 2013 at 05:03:45PM +0200, Sylwester Nawrocki wrote:
> This patch adds common __clk_get(), __clk_put() clkdev helpers which
> replace their platform specific counterparts when the common clock
> API is enabled.
> 
> The owner module pointer field is added to struct clk so a reference
> to the clock supplier module can be taken by the clock consumers.
> 
> Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
> Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>

I'm mostly happy with this now.

> +int __clk_get(struct clk *clk)
> +{
> +	if (clk && !try_module_get(clk->owner))
> +		return 0;
> +
> +	return 1;
> +}
> +EXPORT_SYMBOL(__clk_get);
> +
> +void __clk_put(struct clk *clk)
> +{
> +	if (WARN_ON_ONCE(IS_ERR(clk)))
> +		return;
> +
> +	if (clk)
> +		module_put(clk->owner);
> +}
> +EXPORT_SYMBOL(__clk_put);

Why are these exported?  clkdev can only be built into the kernel, as can
the common clk framework - they can't be modular.  So why would a module
wish to access these directly?

[PATCH v3 3/5] clk: Add common __clk_get(), __clk_put() implementations

[Sylwester Nawrocki]

On 08/24/2013 01:13 AM, Russell King - ARM Linux wrote:
> On Fri, Aug 23, 2013 at 05:03:45PM +0200, Sylwester Nawrocki wrote:
>> >  This patch adds common __clk_get(), __clk_put() clkdev helpers which
>> >  replace their platform specific counterparts when the common clock
>> >  API is enabled.
>> >
>> >  The owner module pointer field is added to struct clk so a reference
>> >  to the clock supplier module can be taken by the clock consumers.
>> >
>> >  Signed-off-by: Sylwester Nawrocki<s.nawrocki@samsung.com>
>> >  Signed-off-by: Kyungmin Park<kyungmin.park@samsung.com>
>
> I'm mostly happy with this now.
>
>> >  +int __clk_get(struct clk *clk)
>> >  +{
>> >  +	if (clk&&  !try_module_get(clk->owner))
>> >  +		return 0;
>> >  +
>> >  +	return 1;
>> >  +}
>> >  +EXPORT_SYMBOL(__clk_get);
>> >  +
>> >  +void __clk_put(struct clk *clk)
>> >  +{
>> >  +	if (WARN_ON_ONCE(IS_ERR(clk)))
>> >  +		return;
>> >  +
>> >  +	if (clk)
>> >  +		module_put(clk->owner);
>> >  +}
>> >  +EXPORT_SYMBOL(__clk_put);
>
> Why are these exported?  clkdev can only be built into the kernel, as can
> the common clk framework - they can't be modular.  So why would a module
> wish to access these directly?

I must have been mislead by the fact that some ARM sub-architecture exports
those, have added them initially and then didn't think enough about it and
left these in. Actually, at some point I noticed the exporting is not 
needed,
but never did get around to remove it. Thanks. The updated series to 
follow.

[PATCH v3 4/5] clk: Assign module owner of a clock being registered

[Sylwester Nawrocki]

Assign module owner of a driver of a device passed to _clk_register()
and __clk_register() functions so the module_{get,put} calls in
__clk_get(), __clk_put() can have required effect.

Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
---
Initially I had an 'owner' field added to struct clk_init_data so it can
be set explicitly in clock providers.  But this required modifications
of all users of (devm_)clk_register() as struct clk_init_data instance
was in most cases an unitialized stack variable.  This would also require
adding yet another argument to various clk_register_* functions
registering the standard clocks.  So I went for assigning clk->owner from
dev->driver->owner.  The disadvantages are that dereferencing dev->driver
may be potentially unsafe when not holding struct device::mutex.  And
there might be cases where clk->owner will need to be NULL.  One option
is to set dev argument of clk_register_*() to NULL for that, but it
predates devm_*.

Presumably a requirement could be added that callers of clk_register*()
must ensure dev->driver won't change during a call to these functions ?
---
 drivers/clk/clk.c |    6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index c173f30..272d68d 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -1692,6 +1692,10 @@ struct clk *__clk_register(struct device *dev, struct clk_hw *hw)
 	clk->flags = hw->init->flags;
 	clk->parent_names = hw->init->parent_names;
 	clk->num_parents = hw->init->num_parents;
+	if (dev && dev->driver)
+		clk->owner = dev->driver->owner;
+	else
+		clk->owner = NULL;

 	ret = __clk_init(dev, clk);
 	if (ret)
@@ -1712,6 +1716,8 @@ static int _clk_register(struct device *dev, struct clk_hw *hw, struct clk *clk)
 		goto fail_name;
 	}
 	clk->ops = hw->init->ops;
+	if (dev && dev->driver)
+		clk->owner = dev->driver->owner;
 	clk->hw = hw;
 	clk->flags = hw->init->flags;
 	clk->num_parents = hw->init->num_parents;
--
1.7.9.5

[PATCH v3 5/5] clk: Implement clk_unregister

[Sylwester Nawrocki]

clk_unregister() is currently not implemented and it is required when
a clock provider module needs to be unloaded.

Normally the clock supplier module is prevented to be unloaded by
taking reference on the module in clk_get().

For cases when the clock supplier module deinitializes despite the
consumers of its clocks holding a reference on the module, e.g. when
the driver is unbound through "unbind" sysfs attribute, there are
empty clock ops added. These ops are assigned temporarily to struct
clk and used until all consumers release the clock, to avoid invoking
callbacks from the module which just got removed.

Signed-off-by: Jiada Wang <jiada_wang@mentor.com>
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
---
Changes since v2:
 - none.

Changes since RFC v1:
 - renamed clk_dummy_* to clk_nodrv_*.

Changes since v3 of the original patch [1]:
 - reparent all children to the orphan list instead of leaving
   the clock unregistered when it has child clocks,
 - removed unnecessary prerequisite checks in clk_debug_unregister(),
 - struct clk is now being freed only when the last clock consumer
   calls clk_put(),
 - empty clock ops are used after clk_unregister() has been called
   until all references to the clock are released and the clock
   object is freed.

[1] http://www.spinics.net/lists/arm-kernel/msg247548.html
---
 drivers/clk/clk.c           |  123 +++++++++++++++++++++++++++++++++++++++++--
 include/linux/clk-private.h |    2 +
 2 files changed, 122 insertions(+), 3 deletions(-)

diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index 272d68d..738c2cc 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -344,6 +344,21 @@ out:
 	return ret;
 }
 
+ /**
+ * clk_debug_unregister - remove a clk node from the debugfs clk tree
+ * @clk: the clk being removed from the debugfs clk tree
+ *
+ * Dynamically removes a clk and all it's children clk nodes from the
+ * debugfs clk tree if clk->dentry points to debugfs created by
+ * clk_debug_register in __clk_init.
+ *
+ * Caller must hold prepare_lock.
+ */
+static void clk_debug_unregister(struct clk *clk)
+{
+	debugfs_remove_recursive(clk->dentry);
+}
+
 /**
  * clk_debug_reparent - reparent clk node in the debugfs clk tree
  * @clk: the clk being reparented
@@ -434,6 +449,9 @@ static inline int clk_debug_register(struct clk *clk) { return 0; }
 static inline void clk_debug_reparent(struct clk *clk, struct clk *new_parent)
 {
 }
+static inline void clk_debug_unregister(struct clk *clk)
+{
+}
 #endif
 
 /* caller must hold prepare_lock */
@@ -1657,6 +1675,7 @@ int __clk_init(struct device *dev, struct clk *clk)
 
 	clk_debug_register(clk);
 
+	kref_init(&clk->ref);
 out:
 	clk_prepare_unlock();
 
@@ -1792,13 +1811,106 @@ fail_out:
 }
 EXPORT_SYMBOL_GPL(clk_register);
 
+/*
+ * Free memory allocated for a clock.
+ * Caller must hold prepare_lock.
+ */
+static void __clk_release(struct kref *ref)
+{
+	struct clk *clk = container_of(ref, struct clk, ref);
+	int i = clk->num_parents;
+
+	kfree(clk->parents);
+	while (--i >= 0)
+		kfree(clk->parent_names[i]);
+
+	kfree(clk->parent_names);
+	kfree(clk->name);
+	kfree(clk);
+}
+
+/*
+ * Empty clk_ops for unregistered clocks. These are used temporarily
+ * after clk_unregister() was called on a clock and until last clock
+ * consumer calls clk_put() and the struct clk object is freed.
+ */
+static int clk_nodrv_prepare_enable(struct clk_hw *hw)
+{
+	return -ENXIO;
+}
+
+static void clk_nodrv_disable_unprepare(struct clk_hw *hw)
+{
+	WARN_ON(1);
+}
+
+static int clk_nodrv_set_rate(struct clk_hw *hw, unsigned long rate,
+					unsigned long parent_rate)
+{
+	return -ENXIO;
+}
+
+static int clk_nodrv_set_parent(struct clk_hw *hw, u8 index)
+{
+	return -ENXIO;
+}
+
+static const struct clk_ops clk_nodrv_ops = {
+	.enable		= clk_nodrv_prepare_enable,
+	.disable	= clk_nodrv_disable_unprepare,
+	.prepare	= clk_nodrv_prepare_enable,
+	.unprepare	= clk_nodrv_disable_unprepare,
+	.set_rate	= clk_nodrv_set_rate,
+	.set_parent	= clk_nodrv_set_parent,
+};
+
 /**
  * clk_unregister - unregister a currently registered clock
  * @clk: clock to unregister
- *
- * Currently unimplemented.
  */
-void clk_unregister(struct clk *clk) {}
+void clk_unregister(struct clk *clk)
+{
+	unsigned long flags;
+
+	clk_prepare_lock();
+
+	if (!clk || IS_ERR(clk)) {
+		pr_err("%s: invalid clock: %p\n", __func__, clk);
+		goto out;
+	}
+
+	if (clk->ops == &clk_nodrv_ops) {
+		pr_err("%s: unregistered clock: %s\n", __func__, clk->name);
+		goto out;
+	}
+	/*
+	 * Assign empty clock ops for consumers that might still hold
+	 * a reference to this clock.
+	 */
+	flags = clk_enable_lock();
+	clk->ops = &clk_nodrv_ops;
+	clk_enable_unlock(flags);
+
+	if (!hlist_empty(&clk->children)) {
+		struct clk *child;
+
+		/* Reparent all children to the orphan list. */
+		hlist_for_each_entry(child, &clk->children, child_node)
+			clk_set_parent(child, NULL);
+	}
+
+	clk_debug_unregister(clk);
+
+	hlist_del_init(&clk->child_node);
+
+	if (clk->prepare_count)
+		pr_warn("%s: unregistering prepared clock: %s\n",
+					__func__, clk->name);
+
+	kref_put(&clk->ref, __clk_release);
+out:
+	clk_prepare_unlock();
+}
 EXPORT_SYMBOL_GPL(clk_unregister);
 
 static void devm_clk_release(struct device *dev, void *res)
@@ -1866,6 +1978,7 @@ int __clk_get(struct clk *clk)
 	if (clk && !try_module_get(clk->owner))
 		return 0;
 
+	kref_get(&clk->ref);
 	return 1;
 }
 EXPORT_SYMBOL(__clk_get);
@@ -1875,6 +1988,10 @@ void __clk_put(struct clk *clk)
 	if (WARN_ON_ONCE(IS_ERR(clk)))
 		return;
 
+	clk_prepare_lock();
+	kref_put(&clk->ref, __clk_release);
+	clk_prepare_unlock();
+
 	if (clk)
 		module_put(clk->owner);
 }
diff --git a/include/linux/clk-private.h b/include/linux/clk-private.h
index b7c0b58..36c1fc8 100644
--- a/include/linux/clk-private.h
+++ b/include/linux/clk-private.h
@@ -12,6 +12,7 @@
 #define __LINUX_CLK_PRIVATE_H
 
 #include <linux/clk-provider.h>
+#include <linux/kref.h>
 #include <linux/list.h>
 
 /*
@@ -47,6 +48,7 @@ struct clk {
 #ifdef CONFIG_COMMON_CLK_DEBUG
 	struct dentry		*dentry;
 #endif
+	struct kref		ref;
 };
 
 /*
-- 
1.7.9.5