Hi Mike,

On Sat, Mar 03, 2012 at 12:29:00AM -0800, Mike Turquette wrote:

[snip]

+static 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->hw);
+
+	if (clk->parent)
+		__clk_disable(clk->parent);

if __clk_xxx handle NULL clk, we might not need to check parent here?
There're also many places that checks parent below.

+}
+
+/**
+ * clk_disable - gate a clock
+ * @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);
+
+static 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);

ditto

+
+		if (ret)
+			return ret;
+
+		if (clk->ops->enable) {
+			ret = clk->ops->enable(clk->hw);
+			if (ret) {
+				__clk_disable(clk->parent);

it's good case that don't check parent is NULL.

+				return ret;
+			}
+		}
+	}
+
+	clk->enable_count++;
+	return 0;
+}
+
+/**
+ * clk_enable - ungate a clock
+ * @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 -EINVAL.
+ */
+unsigned long clk_get_rate(struct clk *clk)
+{
+	unsigned long rate;
+
+	mutex_lock(&prepare_lock);
+	rate = __clk_get_rate(clk);
+	mutex_unlock(&prepare_lock);
+
+	return rate;
+}
+EXPORT_SYMBOL_GPL(clk_get_rate);
+
+/**
+ * __clk_round_rate - round the given rate for a clk
+ * @clk: round the rate of this clock
+ *
+ * Caller must hold prepare_lock.  Useful for clk_ops such as .set_rate
+ */
+unsigned long __clk_round_rate(struct clk *clk, unsigned long rate)
+{
+	if (!clk && !clk->ops->round_rate)

be	         || ?

+		return -EINVAL;
+
+	return clk->ops->round_rate(clk->hw, rate, NULL);
+}
+
+/**
+ * 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)
+{
+	unsigned long ret = rate;
+
+	mutex_lock(&prepare_lock);
+	if (clk && clk->ops->round_rate)
+		ret = __clk_round_rate(clk, rate);
+	mutex_unlock(&prepare_lock);
+
+	return ret;

If clk is NULL, clk_round_rate and __clk_round_rate return different
values. Do you mean it?

+}
+EXPORT_SYMBOL_GPL(clk_round_rate);
+
+/**
+ * __clk_notify - call clk notifier chain
+ * @clk: struct clk * that is changing rate
+ * @msg: clk notifier type (see include/linux/clk.h)
+ * @old_rate: old clk rate
+ * @new_rate: new clk rate
+ *
+ * Triggers a notifier call chain on the clk rate-change notification
+ * for 'clk'.  Passes a pointer to the struct clk and the previous
+ * and current rates to the notifier callback.  Intended to be called by
+ * internal clock code only.  Returns NOTIFY_DONE from the last driver
+ * called if all went well, or NOTIFY_STOP or NOTIFY_BAD immediately if
+ * a driver returns that.
+ */
+static int __clk_notify(struct clk *clk, unsigned long msg,
+		unsigned long old_rate, unsigned long new_rate)
+{
+	struct clk_notifier *cn;
+	struct clk_notifier_data cnd;
+	int ret = NOTIFY_DONE;
+
+	cnd.clk = clk;
+	cnd.old_rate = old_rate;
+	cnd.new_rate = new_rate;
+
+	list_for_each_entry(cn, &clk_notifier_list, node) {
+		if (cn->clk == clk) {
+			ret = srcu_notifier_call_chain(&cn->notifier_head, msg,
+					&cnd);
+			break;
+		}
+	}
+
+	return ret;
+}
+
+/**
+ * __clk_recalc_rates
+ * @clk: first clk in the subtree
+ * @msg: notification type (see include/linux/clk.h)
+ *
+ * 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.
+ *
+ * clk_recalc_rates also propagates the POST_RATE_CHANGE notification,
+ * if necessary.
+ *
+ * Caller must hold prepare_lock.
+ */
+static void __clk_recalc_rates(struct clk *clk, unsigned long msg)
+{
+	unsigned long old_rate;
+	unsigned long parent_rate = 0;
+	struct hlist_node *tmp;
+	struct clk *child;
+
+	old_rate = clk->rate;
+
+	if (clk->parent)
+		parent_rate = clk->parent->rate;
+
+	if (clk->ops->recalc_rate)
+		clk->rate = clk->ops->recalc_rate(clk->hw, parent_rate);
+	else
+		clk->rate = parent_rate;
+
+	/*
+	 * ignore NOTIFY_STOP and NOTIFY_BAD return values for POST_RATE_CHANGE
+	 * & ABORT_RATE_CHANGE notifiers
+	 */
+	if (clk->notifier_count && msg)
+		__clk_notify(clk, msg, old_rate, clk->rate);
+
+	hlist_for_each_entry(child, tmp, &clk->children, child_node)
+		__clk_recalc_rates(child, msg);
+}
+
+/**
+ * __clk_speculate_rates
+ * @clk: first clk in the subtree
+ * @parent_rate: the "future" rate of clk's parent
+ *
+ * Walks the subtree of clks starting with clk, speculating rates as it
+ * goes and firing off PRE_RATE_CHANGE notifications as necessary.
+ *
+ * Unlike clk_recalc_rates, clk_speculate_rates exists only for sending
+ * pre-rate change notifications and returns early if no clks in the
+ * subtree have subscribed to the notifications.
+ *
+ * Caller must hold prepare_lock.
+ */
+static int __clk_speculate_rates(struct clk *clk, unsigned long parent_rate)
+{
+	struct hlist_node *tmp;
+	struct clk *child;
+	unsigned long new_rate;
+	int ret = NOTIFY_DONE;
+
+	if (!clk->ops->recalc_rate)
+		goto out;

When recalc_rate is NULL, it's possible for it and its children to have
notifier too.

+
+	new_rate = clk->ops->recalc_rate(clk->hw, parent_rate);
+
+	/* abort the rate change if a driver returns NOTIFY_BAD */
+	if (clk->notifier_count)
+		ret = __clk_notify(clk, PRE_RATE_CHANGE, clk->rate, new_rate);
+
+	if (ret == NOTIFY_BAD)
+		goto out;
+
+	hlist_for_each_entry(child, tmp, &clk->children, child_node) {
+		ret = __clk_speculate_rates(child, new_rate);
+		if (ret == NOTIFY_BAD)
+			break;
+	}

Tell the notifier that already receive PRE_RATE_CHANGE abort?

+
+out:
+	return ret;
+}
+
+/**
+ * DOC: Using the CLK_SET_RATE_PARENT 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_SET_RATE_GATE flag on any
+ * clk where you also set the CLK_SET_RATE_PARENT flag
+ *
+ * PRE_RATE_CHANGE notifications are supposed to stack as a rate change
+ * request propagates up the clk tree.  This reflects the different
+ * rates that a downstream clk might experience if left enabled while
+ * upstream parents change their rates.
+ */
+static struct clk *__clk_set_rate(struct clk *clk, unsigned long rate)
+{
+	struct clk *fail_clk = NULL;
+	int ret = NOTIFY_DONE;
+	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_SET_RATE_GATE) && 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->hw, rate, &parent_new_rate);
+
+	/* NOTE: pre-rate change notifications will stack */
+	if (clk->notifier_count)
+		ret = __clk_notify(clk, PRE_RATE_CHANGE, clk->rate, new_rate);

if ((clk->flags & CLK_SET_RATE_PARENT) && parent_new_rate)
	dowstream notify from parent clk?

+
+	if (ret == NOTIFY_BAD)
+		return clk;
+
+	/* speculate rate changes down the tree */
+	hlist_for_each_entry(child, tmp, &clk->children, child_node) {
+		ret = __clk_speculate_rates(child, new_rate);
+		if (ret == NOTIFY_BAD)

roll back?

+			return clk;
+	}
+
+	/* change the rate of this clk */
+	if (clk->ops->set_rate)

If set_rate is NULL, it can fail at the beginning of this function.

+		ret = clk->ops->set_rate(clk->hw, new_rate);
+
+	if (ret == NOTIFY_BAD)

you mean to check set_rate fail? Notify ABORT_RATE_CHANGE?

+		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_SET_RATE_PARENT) && 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);
+
+			/*
+			 * Send PRE_RATE_CHANGE notifiers down the tree
+			 * again, since we're rolling back the rate
+			 * changes due to the abort.
+			 *
+			 * Ignore any NOTIFY_BAD's since this *is* the
+			 * exception handler.
+			 *
+			 * NOTE: pre-rate change notifications will stack
+			 */
+			__clk_speculate_rates(clk, clk->parent->rate);

IMHO, driver can not be happy to receive multiple PRE_RATE_CHANGE.
Notify ABORT_RATE_CHANGE?

+
+			clk->ops->set_rate(clk->hw, 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.
+	 */
+	__clk_recalc_rates(clk, POST_RATE_CHANGE);
+
+	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_SET_RATE_GATE 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_SET_RATE_PARENT 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_SET_RATE_PARENT 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);
+		__clk_recalc_rates(clk, ABORT_RATE_CHANGE);

It might need to begin from parent clk. move it to __clk_set_rate?

+		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.  Returns NULL if clk is NULL.
+ */
+struct clk *clk_get_parent(struct clk *clk)
+{
+	struct clk *parent;
+
+	mutex_lock(&prepare_lock);
+	parent = __clk_get_parent(clk);
+	mutex_unlock(&prepare_lock);
+
+	return parent;
+}
+EXPORT_SYMBOL_GPL(clk_get_parent);
+
+/*
+ * .get_parent is mandatory for clocks with multiple possible parents.  It is
+ * optional for single-parent clocks.  Always call .get_parent if it is
+ * available and WARN if it is missing for multi-parent clocks.
+ *
+ * For single-parent clocks without .get_parent, first check to see if the
+ * .parents array exists, and if so use it to avoid an expensive tree
+ * traversal.  If .parents does not exist then walk the tree with __clk_lookup.
+ */
+static struct clk *__clk_init_parent(struct clk *clk)
+{
+	struct clk *ret = NULL;
+	u8 index;
+
+	/* handle the trivial cases */
+
+	if (!clk->num_parents)
+		goto out;
+
+	if (clk->num_parents == 1) {
+		if (IS_ERR_OR_NULL(clk->parent))
+			ret = clk->parent = __clk_lookup(clk->parent_names[0]);
+		ret = clk->parent;
+		goto out;
+	}
+
+	if (!clk->ops->get_parent) {
+		WARN(!clk->ops->get_parent,
+			"%s: multi-parent clocks must implement .get_parent\n",
+			__func__);
+		goto out;
+	};
+
+	/*
+	 * Do our best to cache parent clocks in clk->parents.  This prevents
+	 * unnecessary and expensive calls to __clk_lookup.  We don't set
+	 * clk->parent here; that is done by the calling function
+	 */
+
+	index = clk->ops->get_parent(clk->hw);
+
+	if (!clk->parents)
+		clk->parents =
+			kmalloc((sizeof(struct clk*) * clk->num_parents),
+					GFP_KERNEL);
+
+	if (!clk->parents)
+		ret = __clk_lookup(clk->parent_names[index]);
+	else if (!clk->parents[index])
+		ret = clk->parents[index] =
+			__clk_lookup(clk->parent_names[index]);
+	else
+		ret = clk->parents[index];
+
+out:
+	return ret;
+}
+
+void __clk_reparent(struct clk *clk, struct clk *new_parent)
+{
+#ifdef CONFIG_COMMON_CLK_DEBUG
+	struct dentry *d;
+	struct dentry *new_parent_d;
+#endif
+
+	if (!clk || !new_parent)
+		return;
+
+	hlist_del(&clk->child_node);
+
+	if (new_parent)
+		hlist_add_head(&clk->child_node, &new_parent->children);
+	else
+		hlist_add_head(&clk->child_node, &clk_orphan_list);
+
+#ifdef CONFIG_COMMON_CLK_DEBUG
+	if (!inited)
+		goto out;
+
+	if (new_parent)
+		new_parent_d = new_parent->dentry;
+	else
+		new_parent_d = orphandir;
+
+	d = debugfs_rename(clk->dentry->d_parent, clk->dentry,
+			new_parent_d, clk->name);
+	if (d)
+		clk->dentry = d;
+	else
+		pr_debug("%s: failed to rename debugfs entry for %s\n",
+				__func__, clk->name);
+out:
+#endif
+
+	clk->parent = new_parent;
+
+	__clk_recalc_rates(clk, POST_RATE_CHANGE);
+}
+
+static int __clk_set_parent(struct clk *clk, struct clk *parent)
+{
+	struct clk *old_parent;
+	unsigned long flags;
+	int ret = -EINVAL;
+	u8 i;
+
+	old_parent = clk->parent;
+
+	/* find index of new parent clock using cached parent ptrs */
+	for (i = 0; i < clk->num_parents; i++)
+		if (clk->parents[i] == parent)
+			break;
+
+	/*
+	 * find index of new parent clock using string name comparison
+	 * also try to cache the parent to avoid future calls to __clk_lookup
+	 */
+	if (i == clk->num_parents)
+		for (i = 0; i < clk->num_parents; i++)
+			if (!strcmp(clk->parent_names[i], parent->name)) {
+				clk->parents[i] = __clk_lookup(parent->name);
+				break;
+			}
+
+	if (i == clk->num_parents) {
+		pr_debug("%s: clock %s is not a possible parent of clock %s\n",
+				__func__, parent->name, clk->name);
+		goto out;
+	}
+
+	/* migrate prepare and enable */
+	if (clk->prepare_count)
+		__clk_prepare(parent);
+
+	/* FIXME replace with clk_is_enabled(clk) someday */
+	spin_lock_irqsave(&enable_lock, flags);
+	if (clk->enable_count)
+		__clk_enable(parent);
+	spin_unlock_irqrestore(&enable_lock, flags);
+
+	/* change clock input source */
+	ret = clk->ops->set_parent(clk->hw, i);
+
+	/* clean up old prepare and enable */
+	spin_lock_irqsave(&enable_lock, flags);
+	if (clk->enable_count)
+		__clk_disable(old_parent);
+	spin_unlock_irqrestore(&enable_lock, flags);
+
+	if (clk->prepare_count)
+		__clk_unprepare(old_parent);
+
+out:
+	return ret;
+}
+
+/**
+ * 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_SET_PARENT_GATE 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;
+
+	/* propagate PRE_RATE_CHANGE notifications */
+	if (clk->notifier_count)
+		ret = __clk_speculate_rates(clk, parent->rate);
+
+	/* abort if a driver objects */
+	if (ret == NOTIFY_STOP)
+		goto out;
+
+	/* only re-parent if the clock is not in use */
+	if ((clk->flags & CLK_SET_PARENT_GATE) && clk->prepare_count)
+		ret = -EBUSY;
+	else
+		ret = __clk_set_parent(clk, parent);
+
+	/* propagate ABORT_RATE_CHANGE if .set_parent failed */
+	if (ret) {
+		__clk_recalc_rates(clk, ABORT_RATE_CHANGE);
+		goto out;
+	}
+
+	/* propagate rate recalculation downstream */
+	__clk_reparent(clk, parent);
+
+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.
+ *
+ * Any struct clk passed into __clk_init must have the following members
+ * populated:
+ * 	.name
+ * 	.ops
+ * 	.hw
+ * 	.parent_names
+ * 	.num_parents
+ * 	.flags
+ *
+ * Essentially, everything that would normally be passed into clk_register is
+ * assumed to be initialized already in __clk_init.  The other members may be
+ * populated, but are optional.
+ *
+ * __clk_init is only exposed via clk-private.h and is intended for use with
+ * very large numbers of clocks that need to be statically initialized.  It is
+ * a layering violation to include clk-private.h from any code which implements
+ * a clock's .ops; as such any statically initialized clock data MUST be in a
+ * separate C file from the logic that implements it's operations.
+ */
+void __clk_init(struct device *dev, struct clk *clk)
+{
+	int i;
+	struct clk *orphan;
+	struct hlist_node *tmp;
+
+	if (!clk)
+		return;
+
+	mutex_lock(&prepare_lock);
+
+	/* check to see if a clock with this name is already registered */
+	if (__clk_lookup(clk->name))
+		goto out;
+
+	/*
+	 * Allocate an array of struct clk *'s to avoid unnecessary string
+	 * look-ups of clk's possible parents.  This can fail for clocks passed
+	 * in to clk_init during early boot; thus any access to clk->parents[]
+	 * must always check for a NULL pointer and try to populate it if
+	 * necessary.
+	 *
+	 * If clk->parents is not NULL we skip this entire block.  This allows
+	 * for clock drivers to statically initialize clk->parents.
+	 */
+	if (clk->num_parents && !clk->parents) {
+		clk->parents = kmalloc((sizeof(struct clk*) * clk->num_parents),
+				GFP_KERNEL);
+		/*
+		 * __clk_lookup returns NULL for parents that have not been
+		 * clk_init'd; thus any access to clk->parents[] must check
+		 * for a NULL pointer.  We can always perform lazy lookups for
+		 * missing parents later on.
+		 */
+		if (clk->parents)
+			for (i = 0; i < clk->num_parents; i++)
+				clk->parents[i] =
+					__clk_lookup(clk->parent_names[i]);
+	}
+
+	clk->parent = __clk_init_parent(clk);
+
+	/*
+	 * Populate clk->parent if parent has already been __clk_init'd.  If
+	 * parent has not yet been __clk_init'd then place clk in the orphan
+	 * list.  If clk has set the CLK_IS_ROOT flag then place it in the root
+	 * clk list.
+	 *
+	 * Every time a new clk is clk_init'd then we walk the list of orphan
+	 * clocks and re-parent any that are children of the clock currently
+	 * being clk_init'd.
+	 */
+	if (clk->parent)
+		hlist_add_head(&clk->child_node,
+				&clk->parent->children);
+	else if (clk->flags & CLK_IS_ROOT)
+		hlist_add_head(&clk->child_node, &clk_root_list);
+	else
+		hlist_add_head(&clk->child_node, &clk_orphan_list);
+
+	/*
+	 * Set clk's rate.  The preferred method is to use .recalc_rate.  For
+	 * simple clocks and lazy developers the default fallback is to use the
+	 * parent's rate.  If a clock doesn't have a parent (or is orphaned)
+	 * then rate is set to zero.
+	 */
+	if (clk->ops->recalc_rate)
+		clk->rate = clk->ops->recalc_rate(clk->hw,
+				__clk_get_rate(clk->parent));
+	else if (clk->parent)
+		clk->rate = clk->parent->rate;
+	else
+		clk->rate = 0;
+
+	/*
+	 * walk the list of orphan clocks and reparent any that are children of
+	 * this clock
+	 */
+	hlist_for_each_entry(orphan, tmp, &clk_orphan_list, child_node)
+		__clk_reparent(orphan, __clk_init_parent(orphan));

check whether orphan->parent is the value of  __clk_init_parent(orphan)
before reparent?

+
+	/*
+	 * optional platform-specific magic
+	 *
+	 * The .init callback is not used by any of the basic clock types, but
+	 * exists for weird hardware that must perform initialization magic.
+	 * Please consider other ways of solving initialization problems before
+	 * using this callback, as it's use is discouraged.
+	 */
+	if (clk->ops->init)
+		clk->ops->init(clk->hw);
+
+	clk_debug_register(clk);
+
+out:
+	mutex_unlock(&prepare_lock);
+
+	return;
+}
+
+/**
+ * clk_register - allocate a new clock, register it and return an opaque cookie
+ * @dev: device that is registering this clock
+ * @name: clock name
+ * @ops: operations this clock supports
+ * @hw: link to hardware-specific clock data
+ * @parent_names: array of string names for all possible parents
+ * @num_parents: number of possible parents
+ * @flags: framework-level hints and quirks
+ *
+ * clk_register is the primary interface for populating the clock tree with new
+ * clock nodes.  It returns a pointer to the newly allocated struct clk which
+ * cannot be dereferenced by driver code but may be used in conjuction with the
+ * rest of the clock API.
+ */
+struct clk *clk_register(struct device *dev, const char *name,
+		const struct clk_ops *ops, struct clk_hw *hw,
+		char **parent_names, u8 num_parents, unsigned long flags)
+{
+	struct clk *clk;
+
+	clk = kzalloc(sizeof(*clk), GFP_KERNEL);
+	if (!clk)
+		return NULL;
+
+	clk->name = name;
+	clk->ops = ops;
+	clk->hw = hw;
+	clk->flags = flags;
+	clk->parent_names = parent_names;
+	clk->num_parents = num_parents;
+	hw->clk = clk;
+
+	__clk_init(dev, clk);
+
+	return clk;
+}
+EXPORT_SYMBOL_GPL(clk_register);
+
+/***        clk rate change notifiers        ***/
+
+/**
+ * clk_notifier_register - add a clk rate change notifier
+ * @clk: struct clk * to watch
+ * @nb: struct notifier_block * with callback info
+ *
+ * Request notification when clk's rate changes.  This uses an SRCU
+ * notifier because we want it to block and notifier unregistrations are
+ * uncommon.  The callbacks associated with the notifier must not
+ * re-enter into the clk framework by calling any top-level clk APIs;
+ * this will cause a nested prepare_lock mutex.
+ *
+ * Pre-change notifier callbacks will be passed the current, pre-change
+ * rate of the clk via struct clk_notifier_data.old_rate.  The new,
+ * post-change rate of the clk is passed via struct
+ * clk_notifier.new_rate.

clk_notifier_data ?

+ *
+ * Post-change notifiers will pass the now-current, post-change rate of
+ * the clk in both struct clk_notifier_data.old_rate and struct
+ * clk_notifier_data.new_rate.
+ *
+ * Abort-change notifiers are effectively the opposite of pre-change
+ * notifiers: the original pre-change clk rate is passed in via struct
+ * clk_notifier_data.new_rate and the failed post-change rate is passed
+ * in via struct clk_notifier_data.old_rate.
+ *
+ * clk_notifier_register() must be called from non-atomic context.
+ * Returns -EINVAL if called with null arguments, -ENOMEM upon
+ * allocation failure; otherwise, passes along the return value of
+ * srcu_notifier_chain_register().
+ */
+int clk_notifier_register(struct clk *clk, struct notifier_block *nb)
+{
+	struct clk_notifier *cn;
+	int ret = -ENOMEM;
+
+	if (!clk || !nb)
+		return -EINVAL;
+
+	mutex_lock(&prepare_lock);
+
+	/* search the list of notifiers for this clk */
+	list_for_each_entry(cn, &clk_notifier_list, node)
+		if (cn->clk == clk)
+			break;
+
+	/* if clk wasn't in the notifier list, allocate new clk_notifier */
+	if (cn->clk != clk) {
+		cn = kzalloc(sizeof(struct clk_notifier), GFP_KERNEL);
+		if (!cn)
+			goto out;
+
+		cn->clk = clk;
+		srcu_init_notifier_head(&cn->notifier_head);
+
+		list_add(&cn->node, &clk_notifier_list);
+	}

why not embedd notifier_head to struct clk?

Add: clocks that call __clk_init don't need to call clk_register.

I can not find anywhere check it.

+#define CLK_IS_ROOT		BIT(4) /* root clk, has no parent */
+
+/**
+ * struct clk_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.  The
+ * 		parent rate is an input parameter.  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:	Given a target rate as input, returns the closest rate actually
+ * 		supported by the clock.
+ *
+ * @get_parent:	Queries the hardware to determine the parent of a clock.  The
+ * 		return value is a u8 which specifies the index corresponding to
+ * 		the parent clock.  This index can be applied to either the
+ * 		.parent_names or .parents arrays.  In short, this function
+ * 		translates the parent value read from hardware into an array
+ * 		index.  Currently only called when the clock is initialized by
+ * 		__clk_init.  This callback is mandatory for clocks with
+ * 		multiple parents.  It is optional (and unnecessary) for clocks
+ * 		with 0 or 1 parents.
+ *
+ * @set_parent:	Change the input source of this clock; for clocks with multiple
+ * 		possible parents specify a new parent by passing in the index
+ * 		as a u8 corresponding to the parent in either the .parent_names
+ * 		or .parents arrays.  This function in affect translates an
+ * 		array index into the value programmed into the hardware.
+ * 		Returns 0 on success, -EERROR otherwise.
+ *
+ * @set_rate:	Change the rate of this clock. If this callback returns
+ * 		CLK_SET_RATE_PARENT, 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_ops {
+	int		(*prepare)(struct clk_hw *hw);
+	void		(*unprepare)(struct clk_hw *hw);
+	int		(*enable)(struct clk_hw *hw);
+	void		(*disable)(struct clk_hw *hw);
+	unsigned long	(*recalc_rate)(struct clk_hw *hw,
+					unsigned long parent_rate);
+	long		(*round_rate)(struct clk_hw *hw, unsigned long,
+					unsigned long *);
+	int		(*set_parent)(struct clk_hw *hw, u8 index);
+	u8		(*get_parent)(struct clk_hw *hw);
+	int		(*set_rate)(struct clk_hw *hw, unsigned long);
+	void		(*init)(struct clk_hw *hw);
+};
+
+
+/**
+ * clk_register - allocate a new clock, register it and return an opaque cookie
+ * @dev: device that is registering this clock
+ * @name: clock name
+ * @ops: operations this clock supports
+ * @hw: link to hardware-specific clock data
+ * @parent_names: array of string names for all possible parents
+ * @num_parents: number of possible parents
+ * @flags: framework-level hints and quirks
+ *
+ * clk_register is the primary interface for populating the clock tree with new
+ * clock nodes.  It returns a pointer to the newly allocated struct clk which
+ * cannot be dereferenced by driver code but may be used in conjuction with the
+ * rest of the clock API.
+ */
+struct clk *clk_register(struct device *dev, const char *name,
+		const struct clk_ops *ops, struct clk_hw *hw,
+		char **parent_names, u8 num_parents, unsigned long flags);
+
+/* helper functions */
+const char *__clk_get_name(struct clk *clk);
+struct clk_hw *__clk_get_hw(struct clk *clk);
+u8 __clk_get_num_parents(struct clk *clk);
+struct clk *__clk_get_parent(struct clk *clk);
+unsigned long __clk_get_rate(struct clk *clk);
+unsigned long __clk_get_flags(struct clk *clk);
+struct clk *__clk_lookup(const char *name);
+
+/*
+ * FIXME clock api without lock protection
+ */
+int __clk_prepare(struct clk *clk);
+void __clk_unprepare(struct clk *clk);
+void __clk_reparent(struct clk *clk, struct clk *new_parent);

It only notify POST_RATE_CHANGE without PRE_RATE_CHANGE. Mabe we need
to move PRE_RATE_CHANGE to __clk_reparent too?

+unsigned long __clk_round_rate(struct clk *clk, unsigned long rate);

why're there no enable/disable functions?

Thanks
Richard