The purpose of this function is to be used along with the notifier
mechanism.
When a parent clock can see its rate externally changed at any moment,
and a driver needs a specific clock rate to function, it can register a
notifier on the parent clock, and call clk_set_rate() on the base clock
to adjust its frequency according to the new parent clock.
This works fine, until the base clock has the CLK_SET_RATE_PARENT flag
set. In that case, calling clk_set_rate() on the base clock will call
clk_set_rate() on the parent clock, which will trigger the notifier
again, and we're in a loop.
For that reason, we need to register the notifier on the parent clock of
the first ancestor of the base clock that will effectively modify its
rate when clk_set_rate() is called, which we can now obtain with
clk_get_first_to_set_rate().
Signed-off-by: Paul Cercueil <paul@xxxxxxxxxxxxxxx>
---
drivers/clk/clk.c | 9 +++++++++
include/linux/clk.h | 16 ++++++++++++++++
2 files changed, 25 insertions(+)
diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index 5052541a0986..3fd75e283482 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -2450,6 +2450,15 @@ struct clk *clk_get_parent(struct clk *clk)
}
EXPORT_SYMBOL_GPL(clk_get_parent);
+struct clk *clk_get_first_to_set_rate(struct clk *clk)
+{
+ while (clk && (clk->core->flags & CLK_SET_RATE_PARENT))
+ clk = clk_get_parent(clk);
+
+ return clk;
+}
+
+
static struct clk_core *__clk_init_parent(struct clk_core *core)
{
u8 index = 0;
diff --git a/include/linux/clk.h b/include/linux/clk.h
index 266e8de3cb51..f0ea6ac6aa39 100644
--- a/include/linux/clk.h
+++ b/include/linux/clk.h
@@ -766,6 +766,17 @@ struct clk *clk_get_parent(struct clk *clk);
*/
struct clk *clk_get_sys(const char *dev_id, const char *con_id);
+/**
+ * clk_get_first_to_set_rate - get a pointer to the clock that will
+ * effectively modify its rate when clk_set_rate(clk) is called
+ * (might be clk itself, or any ancestor)
+ * @clk: clock source
+ *
+ * Returns struct clk corresponding to the matched clock source, or
+ * NULL on error.
+ */
+struct clk *clk_get_first_to_set_rate(struct clk *clk);
+
/**
* clk_save_context - save clock context for poweroff
*
@@ -928,6 +939,11 @@ static inline struct clk *clk_get_parent(struct clk *clk)
return NULL;
}
+static inline struct clk *clk_get_first_to_set_rate(struct clk *clk)
+{
+ return NULL;
+}
+
static inline struct clk *clk_get_sys(const char *dev_id, const char *con_id)
{
return NULL;
--
2.30.1
