This patch implements the remaining code for notification of clock
rate changes via the clock framework:
- a notifier registration function, clk_notifier_register()
- a notifier unregistration function, clk_notifier_unregister()
- the clk_notify_post_rate_chg() call-chain function, has been fleshed out
The implementation is via an atomic notifier, called with the clockfw
spinlock held. Callback functions must not sleep and must not re-enter
the clock framework, and should execute quickly.
In the medium-term future, there are likely to be few users of these
notifiers. So, rather than storing one notifier per struct clk,
notifiers are stored in a separate, dynamically allocated list,
effectively trading execution speed (in terms of a sequential scan of
the notifier list) for memory savings. The implementation is
completely hidden from the callbacks and is easily changed if
necessary.
Signed-off-by: Paul Walmsley <paul@xxxxxxxxx>
---
arch/arm/plat-omap/clock.c | 118 +++++++++++++++++++++++++++++++++++++++++++-
1 files changed, 115 insertions(+), 3 deletions(-)
diff --git a/arch/arm/plat-omap/clock.c b/arch/arm/plat-omap/clock.c
index 421d076..354f45f 100644
--- a/arch/arm/plat-omap/clock.c
+++ b/arch/arm/plat-omap/clock.c
@@ -22,6 +22,7 @@
#include <linux/mutex.h>
#include <linux/platform_device.h>
#include <linux/cpufreq.h>
+#include <linux/notifier.h>
#include <linux/debugfs.h>
#include <asm/io.h>
@@ -34,6 +35,8 @@ static DEFINE_SPINLOCK(clockfw_lock);
static struct clk_functions *arch_clock;
+static LIST_HEAD(clk_notifier_list);
+
/*-------------------------------------------------------------------------
* Standard clock functions defined in include/linux/clk.h
*-------------------------------------------------------------------------*/
@@ -380,6 +383,110 @@ EXPORT_SYMBOL(clk_init_cpufreq_table);
#endif
/**
+<<<<<<< current:arch/arm/plat-omap/clock.c
+=======
+ * clk_notifier_register - add a clock rate change notifier
+ * @clk: struct clk * to watch for rate echanges
+ * @nb: struct notifier_block * with callback info
+ *
+ * Request notification after a frequency change on clock 'clk'. This
+ * uses an atomic notifier. The callback will be called with
+ * interrupts disabled; therefore callback code should be very
+ * lightweight. Callback code must not call back into the clock
+ * framework. Callback code will be passed the previous and new rate
+ * of the clock.
+ *
+ * clk_notifier_register() must be called from process
+ * context. Returns -EINVAL if called with null arguments, -ENOMEM
+ * upon allocation failure; otherwise, passes along the return value
+ * of atomic_notifier_chain_register().
+ */
+int clk_notifier_register(struct clk *clk, struct notifier_block *nb)
+{
+ struct clk_notifier *cn = NULL, *cn_new = NULL;
+ int r;
+ unsigned long flags;
+
+ if (!clk || !nb)
+ return -EINVAL;
+
+ /* Allocate this here speculatively so we can avoid GFP_ATOMIC */
+ cn_new = kzalloc(sizeof(struct clk_notifier), GFP_KERNEL);
+ if (!cn_new)
+ return -ENOMEM;
+
+ spin_lock_irqsave(&clockfw_lock, flags);
+
+ list_for_each_entry(cn, &clk_notifier_list, node) {
+ if (cn->clk == clk)
+ break;
+ }
+
+ if (cn->clk != clk) {
+ cn_new->clk = clk;
+ ATOMIC_INIT_NOTIFIER_HEAD(&cn_new->notifier_head);
+
+ list_add(&cn_new->node, &clk_notifier_list);
+ cn = cn_new;
+ } else {
+ kfree(cn_new); /* didn't need it after all */
+ }
+
+ r = atomic_notifier_chain_register(&cn->notifier_head, nb);
+
+ spin_unlock_irqrestore(&clockfw_lock, flags);
+
+ return r;
+}
+
+/**
+ * clk_notifier_unregister - remove a clock rate change notifier
+ * @clk: struct clk *
+ * @nb: struct notifier_block * with callback info
+ *
+ * Request no further notification for frequency changes on clock
+ * 'clk'. This function presently does not release memory allocated
+ * by its corresponding _register function; see inline comments for
+ * more informations. Returns -EINVAL if called with null arguments;
+ * otherwise, passes along the return value of
+ * atomic_notifier_chain_unregister().
+ */
+int clk_notifier_unregister(struct clk *clk, struct notifier_block *nb)
+{
+ struct clk_notifier *cn = NULL;
+ int r = -EINVAL;
+ unsigned long flags;
+
+ if (!clk || !nb)
+ return -EINVAL;
+
+ spin_lock_irqsave(&clockfw_lock, flags);
+
+ list_for_each_entry(cn, &clk_notifier_list, node) {
+ if (cn->clk == clk)
+ break;
+ }
+
+ if (cn->clk == clk) {
+ r = atomic_notifier_chain_unregister(&cn->notifier_head, nb);
+
+ /*
+ * XXX unfortunately it seems that there is no polite
+ * way to test if a notifier has zero users. So once
+ * a post-notifier has been registered on a clock,
+ * that struct clk_notifier will not be freed, even if
+ * all of its users unregister.
+ */
+ } else {
+ r = -ENOENT;
+ }
+
+ spin_unlock_irqrestore(&clockfw_lock, flags);
+
+ return r;
+}
+
+/**
* clk_notify_post_rate_chg - call post-clk-rate-change notifier chain
* @clk: struct clk * that is changing rate
* @old_rate: old rate
@@ -400,11 +507,16 @@ void clk_notify_post_rate_chg(struct clk *clk, unsigned long old_rate,
cnd.old_rate = old_rate;
cnd.new_rate = new_rate;
- /* XXX Call notifier here */
-
+ list_for_each_entry(cn, &clk_notifier_list, node) {
+ if (cn->clk == clk) {
+ atomic_notifier_call_chain(&cn->notifier_head,
+ CLK_POST_RATE_CHANGE,
+ &cnd);
+ break;
+ }
+ }
}
-
/*-------------------------------------------------------------------------*/
#ifdef CONFIG_OMAP_RESET_CLOCKS
--
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