[PATCH v4 3/6] clk: introduce the common clock framework

[Mike Turquette]

The common clk framework is an attempt to define a common struct clk
which can be used by most platforms, and an API that drivers can always
use safely for managing clks.

The net result is consolidation of many different struct clk definitions
and platform-specific clk framework implementations.

This patch introduces the common struct clk, struct clk_ops and
definitions for the long-standing clk API in include/clk/clk.h.
Platforms may define their own hardware-specific clk structure, so long
as it wraps an instance of the common struct clk which is passed to
clk_init at initialization time.  From this point on all of the usual
clk APIs should be supported, so long as the platform supports them
through hardware-specific callbacks in struct clk_ops.

See Documentation/clk.txt for more details.

This patch is based on the work of Jeremy Kerr, which in turn was based
on the work of Ben Herrenschmidt.  Big thanks to both of them for
kickstarting this effort.

Signed-off-by: Mike Turquette <mturquette at linaro.org>
Cc: Jeremy Kerr <jeremy.kerr at canonical.com>
---
 drivers/clk/Kconfig  |    4 +
 drivers/clk/Makefile |    1 +
 drivers/clk/clk.c    |  564 ++++++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/clk.h  |  130 +++++++++++-
 4 files changed, 695 insertions(+), 4 deletions(-)
 create mode 100644 drivers/clk/clk.c

diff --git a/drivers/clk/Kconfig b/drivers/clk/Kconfig
index 7a9899bd..adc0586 100644
--- a/drivers/clk/Kconfig
+++ b/drivers/clk/Kconfig
@@ -8,3 +8,7 @@ config HAVE_MACH_CLKDEV
 
 config HAVE_CLK_PREPARE
 	bool
+
+config GENERIC_CLK
+	bool
+	select HAVE_CLK_PREPARE
diff --git a/drivers/clk/Makefile b/drivers/clk/Makefile
index 07613fa..570d5b9 100644
--- a/drivers/clk/Makefile
+++ b/drivers/clk/Makefile
@@ -1,2 +1,3 @@
 
 obj-$(CONFIG_CLKDEV_LOOKUP)	+= clkdev.o
+obj-$(CONFIG_GENERIC_CLK)	+= clk.o
diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
new file mode 100644
index 0000000..8cadadd
--- /dev/null
+++ b/drivers/clk/clk.c
@@ -0,0 +1,564 @@
+/*
+ * Copyright (C) 2010-2011 Canonical Ltd <jeremy.kerr at canonical.com>
+ * Copyright (C) 2011 Linaro Ltd <mturquette at linaro.org>
+ *
+ * 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.
+ *
+ * Standard functionality for the common clock API.  See Documentation/clk.txt
+ */
+
+#include <linux/clk.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/spinlock.h>
+#include <linux/err.h>
+#include <linux/list.h>
+
+static DEFINE_SPINLOCK(enable_lock);
+static DEFINE_MUTEX(prepare_lock);
+
+static HLIST_HEAD(clk_root_list);
+
+/***        clk API        ***/
+
+void __clk_unprepare(struct clk *clk)
+{
+	if (!clk)
+		return;
+
+	if (WARN_ON(clk->prepare_count == 0))
+		return;
+
+	if (--clk->prepare_count > 0)
+		return;
+
+	WARN_ON(clk->enable_count > 0);
+
+	if (clk->ops->unprepare)
+		clk->ops->unprepare(clk);
+
+	__clk_unprepare(clk->parent);
+}
+
+/**
+ * clk_unprepare - perform the slow part of a clk gate
+ * @clk: the clk being gated
+ *
+ * clk_unprepare may sleep, which differentiates it from clk_disable.  In a
+ * simple case, clk_unprepare can be used instead of clk_disable to gate a clk
+ * if the operation may sleep.  One example is a clk which is accessed over
+ * I2c.  In the complex case a clk gate operation may require a fast and a slow
+ * part.  It is this reason that clk_unprepare and clk_disable are not mutually
+ * exclusive.  In fact clk_disable must be called before clk_unprepare.
+ */
+void clk_unprepare(struct clk *clk)
+{
+	mutex_lock(&prepare_lock);
+	__clk_unprepare(clk);
+	mutex_unlock(&prepare_lock);
+}
+EXPORT_SYMBOL_GPL(clk_unprepare);
+
+int __clk_prepare(struct clk *clk)
+{
+	int ret = 0;
+
+	if (!clk)
+		return 0;
+
+	if (clk->prepare_count == 0) {
+		ret = __clk_prepare(clk->parent);
+		if (ret)
+			return ret;
+
+		if (clk->ops->prepare) {
+			ret = clk->ops->prepare(clk);
+			if (ret) {
+				__clk_unprepare(clk->parent);
+				return ret;
+			}
+		}
+	}
+
+	clk->prepare_count++;
+
+	return 0;
+}
+
+/**
+ * clk_prepare - perform the slow part of a clk ungate
+ * @clk: the clk being ungated
+ *
+ * clk_prepare may sleep, which differentiates it from clk_enable.  In a simple
+ * case, clk_prepare can be used instead of clk_enable to ungate a clk if the
+ * operation may sleep.  One example is a clk which is accessed over I2c.  In
+ * the complex case a clk ungate operation may require a fast and a slow part.
+ * It is this reason that clk_prepare and clk_enable are not mutually
+ * exclusive.  In fact clk_prepare must be called before clk_enable.
+ * Returns 0 on success, -EERROR otherwise.
+ */
+int clk_prepare(struct clk *clk)
+{
+	int ret;
+
+	mutex_lock(&prepare_lock);
+	ret = __clk_prepare(clk);
+	mutex_unlock(&prepare_lock);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(clk_prepare);
+
+void __clk_disable(struct clk *clk)
+{
+	if (!clk)
+		return;
+
+	if (WARN_ON(clk->enable_count == 0))
+		return;
+
+	if (--clk->enable_count > 0)
+		return;
+
+	if (clk->ops->disable)
+		clk->ops->disable(clk);
+
+	if (clk->parent)
+		__clk_disable(clk->parent);
+}
+
+/**
+ * clk_disable - perform the fast part of a clk gate
+ * @clk: the clk being gated
+ *
+ * clk_disable must not sleep, which differentiates it from clk_unprepare.  In
+ * a simple case, clk_disable can be used instead of clk_unprepare to gate a
+ * clk if the operation is fast and will never sleep.  One example is a
+ * SoC-internal clk which is controlled via simple register writes.  In the
+ * complex case a clk gate operation may require a fast and a slow part.  It is
+ * this reason that clk_unprepare and clk_disable are not mutually exclusive.
+ * In fact clk_disable must be called before clk_unprepare.
+ */
+void clk_disable(struct clk *clk)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&enable_lock, flags);
+	__clk_disable(clk);
+	spin_unlock_irqrestore(&enable_lock, flags);
+}
+EXPORT_SYMBOL_GPL(clk_disable);
+
+int __clk_enable(struct clk *clk)
+{
+	int ret = 0;
+
+	if (!clk)
+		return 0;
+
+	if (WARN_ON(clk->prepare_count == 0))
+		return -ESHUTDOWN;
+
+	if (clk->enable_count == 0) {
+		if (clk->parent)
+			ret = __clk_enable(clk->parent);
+
+		if (ret)
+			return ret;
+
+		if (clk->ops->enable) {
+			ret = clk->ops->enable(clk);
+			if (ret) {
+				__clk_disable(clk->parent);
+				return ret;
+			}
+		}
+	}
+
+	clk->enable_count++;
+	return 0;
+}
+
+/**
+ * clk_enable - perform the fast part of a clk ungate
+ * @clk: the clk being ungated
+ *
+ * clk_enable must not sleep, which differentiates it from clk_prepare.  In a
+ * simple case, clk_enable can be used instead of clk_prepare to ungate a clk
+ * if the operation will never sleep.  One example is a SoC-internal clk which
+ * is controlled via simple register writes.  In the complex case a clk ungate
+ * operation may require a fast and a slow part.  It is this reason that
+ * clk_enable and clk_prepare are not mutually exclusive.  In fact clk_prepare
+ * must be called before clk_enable.  Returns 0 on success, -EERROR
+ * otherwise.
+ */
+int clk_enable(struct clk *clk)
+{
+	unsigned long flags;
+	int ret;
+
+	spin_lock_irqsave(&enable_lock, flags);
+	ret = __clk_enable(clk);
+	spin_unlock_irqrestore(&enable_lock, flags);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(clk_enable);
+
+/**
+ * clk_get_rate - return the rate of clk
+ * @clk: the clk whose rate is being returned
+ *
+ * Simply returns the cached rate of the clk.  Does not query the hardware.  If
+ * clk is NULL then returns 0.
+ */
+unsigned long clk_get_rate(struct clk *clk)
+{
+	unsigned long rate;
+
+	if (!clk)
+		return 0;
+
+	mutex_lock(&prepare_lock);
+	rate = clk->rate;
+	mutex_unlock(&prepare_lock);
+
+	return rate;
+}
+EXPORT_SYMBOL_GPL(clk_get_rate);
+
+/**
+ * clk_round_rate - round the given rate for a clk
+ * @clk: the clk for which we are rounding a rate
+ * @rate: the rate which is to be rounded
+ *
+ * Takes in a rate as input and rounds it to a rate that the clk can actually
+ * use which is then returned.  If clk doesn't support round_rate operation
+ * then the rate passed in is returned.
+ */
+long clk_round_rate(struct clk *clk, unsigned long rate)
+{
+	if (clk && clk->ops->round_rate)
+		return clk->ops->round_rate(clk, rate, NULL);
+
+	return rate;
+}
+EXPORT_SYMBOL_GPL(clk_round_rate);
+
+/**
+ * __clk_recalc_rates
+ * @clk: first clk in the subtree
+ *
+ * Walks the subtree of clks starting with clk and recalculates rates as it
+ * goes.  Note that if a clk does not implement the recalc_rate operation then
+ * propagation of that subtree stops and all of that clks children will not
+ * have their rates updated.  Caller must hold prepare_lock.
+ */
+static void __clk_recalc_rates(struct clk *clk)
+{
+	struct hlist_node *tmp;
+	struct clk *child;
+
+	if (!clk->ops->recalc_rate) {
+		pr_debug("%s: no .recalc_rate for clk %s\n",
+				__func__, clk->name);
+		return;
+	}
+
+	clk->rate = clk->ops->recalc_rate(clk);
+
+	/* FIXME add post-rate change notification here */
+
+	hlist_for_each_entry(child, tmp, &clk->children, child_node)
+		__clk_recalc_rates(child);
+}
+
+/**
+ * DOC: Using the CLK_PARENT_SET_RATE flag
+ *
+ * __clk_set_rate changes the child's rate before the parent's to more
+ * easily handle failure conditions.
+ *
+ * This means clk might run out of spec for a short time if its rate is
+ * increased before the parent's rate is updated.
+ *
+ * To prevent this consider setting the CLK_GATE_SET_RATE flag on any
+ * clk where you also set the CLK_PARENT_SET_RATE flag
+ */
+struct clk *__clk_set_rate(struct clk *clk, unsigned long rate)
+{
+	struct clk *fail_clk = NULL;
+	int ret = 0;
+	unsigned long old_rate = clk->rate;
+	unsigned long new_rate;
+	unsigned long parent_old_rate;
+	unsigned long parent_new_rate = 0;
+	struct clk *child;
+	struct hlist_node *tmp;
+
+	/* bail early if we can't change rate while clk is enabled */
+	if ((clk->flags & CLK_GATE_SET_RATE) && clk->enable_count)
+		return clk;
+
+	/* find the new rate and see if parent rate should change too */
+	WARN_ON(!clk->ops->round_rate);
+
+	new_rate = clk->ops->round_rate(clk, rate, &parent_new_rate);
+
+	/* FIXME propagate pre-rate change notification here */
+	/* XXX note that pre-rate change notifications will stack */
+
+	/* change the rate of this clk */
+	if (clk->ops->set_rate)
+		ret = clk->ops->set_rate(clk, new_rate);
+
+	if (ret)
+		return clk;
+
+	/*
+	 * change the rate of the parent clk if necessary
+	 *
+	 * hitting the nested 'if' path implies we have hit a .set_rate
+	 * failure somewhere upstream while propagating __clk_set_rate
+	 * up the clk tree.  roll back the clk rates one by one and
+	 * return the pointer to the clk that failed.  clk_set_rate will
+	 * use the pointer to propagate a rate-change abort notifier
+	 * from the "highest" point.
+	 */
+	if ((clk->flags & CLK_PARENT_SET_RATE) && parent_new_rate) {
+		parent_old_rate = clk->parent->rate;
+		fail_clk = __clk_set_rate(clk->parent, parent_new_rate);
+
+		/* roll back changes if parent rate change failed */
+		if (fail_clk) {
+			pr_warn("%s: failed to set parent %s rate to %lu\n",
+					__func__, fail_clk->name,
+					parent_new_rate);
+			clk->ops->set_rate(clk, old_rate);
+		}
+		return fail_clk;
+	}
+
+	/*
+	 * set clk's rate & recalculate the rates of clk's children
+	 *
+	 * hitting this path implies we have successfully finished
+	 * propagating recursive calls to __clk_set_rate up the clk tree
+	 * (if necessary) and it is safe to propagate __clk_recalc_rates
+	 * and post-rate change notifiers down the clk tree from this
+	 * point.
+	 */
+	/* FIXME propagate post-rate change notifier starting with this clk */
+	__clk_recalc_rates(clk);
+
+	return NULL;
+}
+
+/**
+ * clk_set_rate - specify a new rate for clk
+ * @clk: the clk whose rate is being changed
+ * @rate: the new rate for clk
+ *
+ * In the simplest case clk_set_rate will only change the rate of clk.
+ *
+ * If clk has the CLK_GATE_SET_RATE flag set and it is enabled this call
+ * will fail; only when the clk is disabled will it be able to change
+ * its rate.
+ *
+ * Setting the CLK_PARENT_SET_RATE flag allows clk_set_rate to
+ * recursively propagate up to clk's parent; whether or not this happens
+ * depends on the outcome of clk's .round_rate implementation.  If
+ * *parent_rate is 0 after calling .round_rate then upstream parent
+ * propagation is ignored.  If *parent_rate comes back with a new rate
+ * for clk's parent then we propagate up to clk's parent and set it's
+ * rate.  Upward propagation will continue until either a clk does not
+ * support the CLK_PARENT_SET_RATE flag or .round_rate stops requesting
+ * changes to clk's parent_rate.  If there is a failure during upstream
+ * propagation then clk_set_rate will unwind and restore each clk's rate
+ * that had been successfully changed.  Afterwards a rate change abort
+ * notification will be propagated downstream, starting from the clk
+ * that failed.
+ *
+ * At the end of all of the rate setting, clk_set_rate internally calls
+ * __clk_recalc_rates and propagates the rate changes downstream,
+ * starting from the highest clk whose rate was changed.  This has the
+ * added benefit of propagating post-rate change notifiers.
+ *
+ * Note that while post-rate change and rate change abort notifications
+ * are guaranteed to be sent to a clk only once per call to
+ * clk_set_rate, pre-change notifications will be sent for every clk
+ * whose rate is changed.  Stacking pre-change notifications is noisy
+ * for the drivers subscribed to them, but this allows drivers to react
+ * to intermediate clk rate changes up until the point where the final
+ * rate is achieved at the end of upstream propagation.
+ *
+ * Returns 0 on success, -EERROR otherwise.
+ */
+int clk_set_rate(struct clk *clk, unsigned long rate)
+{
+	struct clk *fail_clk;
+	int ret = 0;
+
+	/* prevent racing with updates to the clock topology */
+	mutex_lock(&prepare_lock);
+
+	/* bail early if nothing to do */
+	if (rate == clk->rate)
+		goto out;
+
+	fail_clk = __clk_set_rate(clk, rate);
+	if (fail_clk) {
+		pr_warn("%s: failed to set %s rate\n", __func__,
+				fail_clk->name);
+		/* FIXME propagate rate change abort notification here */
+		ret = -EIO;
+	}
+out:
+	mutex_unlock(&prepare_lock);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(clk_set_rate);
+
+/**
+ * clk_get_parent - return the parent of a clk
+ * @clk: the clk whose parent gets returned
+ *
+ * Simply returns clk->parent.  It is up to the caller to hold the
+ * prepare_lock, if desired.  Returns NULL if clk is NULL.
+ */
+struct clk *clk_get_parent(struct clk *clk)
+{
+	struct clk *parent;
+
+	if (!clk)
+		return NULL;
+
+	mutex_lock(&prepare_lock);
+	parent = clk->parent;
+	mutex_unlock(&prepare_lock);
+
+	return parent;
+}
+EXPORT_SYMBOL_GPL(clk_get_parent);
+
+void __clk_reparent(struct clk *clk, struct clk *new_parent)
+{
+	if (!clk || !new_parent)
+		return;
+
+	hlist_del(&clk->child_node);
+	hlist_add_head(&clk->child_node, &new_parent->children);
+
+	clk->parent = new_parent;
+
+	/* FIXME update sysfs clock topology */
+}
+
+/**
+ * clk_set_parent - switch the parent of a mux clk
+ * @clk: the mux clk whose input we are switching
+ * @parent: the new input to clk
+ *
+ * Re-parent clk to use parent as it's new input source.  If clk has the
+ * CLK_GATE_SET_PARENT flag set then clk must be gated for this
+ * operation to succeed.  After successfully changing clk's parent
+ * clk_set_parent will update the clk topology, sysfs topology and
+ * propagate rate recalculation via __clk_recalc_rates.  Returns 0 on
+ * success, -EERROR otherwise.
+ */
+int clk_set_parent(struct clk *clk, struct clk *parent)
+{
+	int ret = 0;
+
+	if (!clk || !clk->ops)
+		return -EINVAL;
+
+	if (!clk->ops->set_parent)
+		return -ENOSYS;
+
+	/* prevent racing with updates to the clock topology */
+	mutex_lock(&prepare_lock);
+
+	if (clk->parent == parent)
+		goto out;
+
+	/* FIXME add pre-rate change notification here */
+
+	/* only re-parent if the clock is not in use */
+	if ((clk->flags & CLK_GATE_SET_PARENT) && clk->prepare_count)
+		ret = -EBUSY;
+	else
+		ret = clk->ops->set_parent(clk, parent);
+
+	if (ret < 0)
+		/* FIXME add rate change abort notification here */
+		goto out;
+
+	/* update tree topology */
+	__clk_reparent(clk, parent);
+
+	/*
+	 * If successful recalculate the rates of the clock, including
+	 * children.
+	 */
+	__clk_recalc_rates(clk);
+
+out:
+	mutex_unlock(&prepare_lock);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(clk_set_parent);
+
+/**
+ * clk_init - initialize the data structures in a struct clk
+ * @dev: device initializing this clk, placeholder for now
+ * @clk: clk being initialized
+ *
+ * Initializes the lists in struct clk, queries the hardware for the
+ * parent and rate and sets them both.  Adds the clk to the sysfs tree
+ * topology.
+ *
+ * Caller must populate clk->name and clk->flags before calling
+ * clk_init.  A key assumption in the call to .get_parent is that clks
+ * are being initialized in-order.
+ */
+void clk_init(struct device *dev, struct clk *clk)
+{
+	if (!clk)
+		return;
+
+	INIT_HLIST_HEAD(&clk->children);
+	INIT_HLIST_NODE(&clk->child_node);
+
+	mutex_lock(&prepare_lock);
+
+	/*
+	 * .get_parent is mandatory for populating .parent for clks with
+	 * multiple possible parents.  For clks with a fixed parent
+	 * .get_parent is not mandatory and .parent can be statically
+	 * initialized
+	 */
+	if (clk->ops->get_parent)
+		clk->parent = clk->ops->get_parent(clk);
+
+	/* clks without a parent are considered root clks */
+	if (clk->parent)
+		hlist_add_head(&clk->child_node,
+				&clk->parent->children);
+	else
+		hlist_add_head(&clk->child_node, &clk_root_list);
+
+	if (clk->ops->recalc_rate)
+		clk->rate = clk->ops->recalc_rate(clk);
+	else
+		clk->rate = 0;
+
+	mutex_unlock(&prepare_lock);
+
+	return;
+}
+EXPORT_SYMBOL_GPL(clk_init);
diff --git a/include/linux/clk.h b/include/linux/clk.h
index 7213b52..9cb8d72 100644
--- a/include/linux/clk.h
+++ b/include/linux/clk.h
@@ -3,6 +3,8 @@
  *
  *  Copyright (C) 2004 ARM Limited.
  *  Written by Deep Blue Solutions Limited.
+ *  Copyright (c) 2010-2011 Jeremy Kerr <jeremy.kerr at canonical.com>
+ *  Copyright (C) 2011 Linaro Ltd <mturquette at linaro.org>
  *
  * 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
@@ -12,18 +14,137 @@
 #define __LINUX_CLK_H
 
 #include <linux/kernel.h>
+#include <linux/errno.h>
 
 struct device;
 
+struct clk;
+
+#ifdef CONFIG_GENERIC_CLK
+
 /*
- * The base API.
+ * flags used across common struct clk.  these flags should only affect the
+ * top-level framework.  custom flags for dealing with hardware specifics
+ * belong in struct clk_hw_your_unique_device
  */
+#define CLK_GATE_SET_RATE	BIT(0) /* must be gated across rate change */
+#define CLK_GATE_SET_PARENT	BIT(1) /* must be gated across re-parent */
+#define CLK_PARENT_SET_RATE	BIT(2) /* propagate rate change up one level */
+#define CLK_IGNORE_UNUSED	BIT(3) /* do not gate even if unused */
 
+#define CLK_GATE_RATE_CHANGE	(CLK_GATE_SET_RATE | CLK_GATE_SET_PARENT)
 
-/*
- * struct clk - an machine class defined object / cookie.
+struct clk {
+	const char		*name;
+	const struct clk_hw_ops	*ops;
+	struct clk		*parent;
+	unsigned long		rate;
+	unsigned long		flags;
+	unsigned int		enable_count;
+	unsigned int		prepare_count;
+	struct hlist_head	children;
+	struct hlist_node	child_node;
+};
+
+/**
+ * struct clk_hw_ops -  Callback operations for hardware clocks; these are to
+ * be provided by the clock implementation, and will be called by drivers
+ * through the clk_* API.
+ *
+ * @prepare:	Prepare the clock for enabling. This must not return until
+ * 		the clock is fully prepared, and it's safe to call clk_enable.
+ * 		This callback is intended to allow clock implementations to
+ * 		do any initialisation that may sleep. Called with
+ * 		prepare_lock held.
+ *
+ * @unprepare:	Release the clock from its prepared state. This will typically
+ * 		undo any work done in the @prepare callback. Called with
+ * 		prepare_lock held.
+ *
+ * @enable:	Enable the clock atomically. This must not return until the
+ * 		clock is generating a valid clock signal, usable by consumer
+ * 		devices. Called with enable_lock held. This function must not
+ * 		sleep.
+ *
+ * @disable:	Disable the clock atomically. Called with enable_lock held.
+ * 		This function must not sleep.
+ *
+ * @recalc_rate	Recalculate the rate of this clock, by quering hardware
+ * 		and/or the clock's parent. It is up to the caller to insure
+ * 		that the prepare_mutex is held across this call.  Returns the
+ * 		calculated rate.  Optional, but recommended - if this op is not
+ * 		set then clock rate will be initialized to 0.
+ *
+ * @round_rate	XXX FIXME
+ *
+ * @get_parent	Return the parent of this clock; for clocks with multiple
+ * 		possible parents, query the hardware for the current parent.
+ * 		Clocks with fixed parents should still implement this and
+ * 		return something like struct clk *fixed_parent from their
+ * 		respective struct clk_hw_* data.  Currently called only when
+ * 		the clock is initialized.  Clocks that do not implement this
+ * 		will have their parent set to NULL.
+ *
+ * @set_parent	Change the input source of this clock; for clocks with multiple
+ * 		possible parents specify a new parent by passing in a struct
+ * 		clk *parent.  Returns 0 on success, -EERROR otherwise.
+ *
+ * @set_rate	Change the rate of this clock. If this callback returns
+ * 		CLK_PARENT_SET_RATE, the rate change will be propagated to the
+ * 		parent clock (which may propagate again if the parent clock
+ * 		also sets this flag). The requested rate of the parent is
+ * 		passed back from the callback in the second 'unsigned long *'
+ * 		argument.  Note that it is up to the hardware clock's set_rate
+ * 		implementation to insure that clocks do not run out of spec
+ * 		when propgating the call to set_rate up to the parent.  One way
+ * 		to do this is to gate the clock (via clk_disable and/or
+ * 		clk_unprepare) before calling clk_set_rate, then ungating it
+ * 		afterward.  If your clock also has the CLK_GATE_SET_RATE flag
+ * 		set then this will insure safety.  Returns 0 on success,
+ * 		-EERROR otherwise.
+ *
+ * The clk_enable/clk_disable and clk_prepare/clk_unprepare pairs allow
+ * implementations to split any work between atomic (enable) and sleepable
+ * (prepare) contexts.  If enabling a clock requires code that might sleep,
+ * this must be done in clk_prepare.  Clock enable code that will never be
+ * called in a sleepable context may be implement in clk_enable.
+ *
+ * Typically, drivers will call clk_prepare when a clock may be needed later
+ * (eg. when a device is opened), and clk_enable when the clock is actually
+ * required (eg. from an interrupt). Note that clk_prepare MUST have been
+ * called before clk_enable.
  */
-struct clk;
+struct clk_hw_ops {
+	int		(*prepare)(struct clk *clk);
+	void		(*unprepare)(struct clk *clk);
+	int		(*enable)(struct clk *clk);
+	void		(*disable)(struct clk *clk);
+	unsigned long	(*recalc_rate)(struct clk *clk);
+	long		(*round_rate)(struct clk *clk, unsigned long,
+					unsigned long *);
+	int		(*set_parent)(struct clk *clk, struct clk *);
+	struct clk *	(*get_parent)(struct clk *clk);
+	int		(*set_rate)(struct clk *clk, unsigned long);
+};
+
+/**
+ * clk_init - initialize the data structures in a struct clk
+ * @dev: device initializing this clk, placeholder for now
+ * @clk: clk being initialized
+ *
+ * Initializes the lists in struct clk, queries the hardware for the
+ * parent and rate and sets them both.  Adds the clk to the sysfs tree
+ * topology.
+ *
+ * Caller must populate .name, .flags and .ops before calling clk_init.
+ */
+void clk_init(struct device *dev, struct clk *clk);
+
+int __clk_prepare(struct clk *clk);
+void __clk_unprepare(struct clk *clk);
+void __clk_reparent(struct clk *clk, struct clk *new_parent);
+
+#endif /* !CONFIG_GENERIC_CLK */
 
 /**
  * clk_get - lookup and obtain a reference to a clock producer.
@@ -110,6 +231,7 @@ static inline void clk_unprepare(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.
+ *		  Returns zero if the clock rate is unknown.
  * @clk: clock source
  */
 unsigned long clk_get_rate(struct clk *clk);
-- 
1.7.5.4