From: Thierry Reding <treding@xxxxxxxxxx>
This new function is similar to clk_set_parent(), except that it doesn't
actually change the parent. It merely checks that the given parent clock
can be a parent for the given clock.
A situation where this is useful is to check that a particular setup is
valid before switching to it. One specific use-case for this is atomic
modesetting in the DRM framework where setting a mode is divided into a
check phase where a given configuration is validated before applying
changes to the hardware.
Cc: Russell King <linux@xxxxxxxxxxxxxxxx>
Cc: Mike Turquette <mturquette@xxxxxxxxxx>
Cc: Stephen Boyd <sboyd@xxxxxxxxxxxxxx>
Signed-off-by: Thierry Reding <treding@xxxxxxxxxx>
---
drivers/clk/clk.c | 36 ++++++++++++++++++++++++++++++++++++
include/linux/clk.h | 14 ++++++++++++++
2 files changed, 50 insertions(+)
diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index af06b7377d37..297910815dea 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -1672,6 +1672,42 @@ void __clk_reparent(struct clk *clk, struct clk *new_parent)
}
/**
+ * clk_try_parent - check if a clock can be the parent clock source of another
+ * @clk: clock source
+ * @parent: parent clock source
+ *
+ * This is like clk_set_parent(), except that it only checks that parent can
+ * be the parent clock source for clock.
+ *
+ * Returns success (0) or negative errno.
+ */
+int clk_try_parent(struct clk *clk, struct clk *parent)
+{
+ int err = 0;
+
+ if (!clk || !parent)
+ return -EINVAL;
+
+ if ((clk->num_parents > 1) && !clk->ops->set_parent)
+ return -ENOSYS;
+
+ clk_prepare_lock();
+
+ if (clk->parent == parent)
+ goto unlock;
+
+ err = clk_fetch_parent_index(clk, parent);
+ if (err > 0)
+ err = 0;
+
+unlock:
+ clk_prepare_unlock();
+
+ return err;
+}
+EXPORT_SYMBOL_GPL(clk_try_parent);
+
+/**
* 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
diff --git a/include/linux/clk.h b/include/linux/clk.h
index fb1ac65f127c..94da8c68a515 100644
--- a/include/linux/clk.h
+++ b/include/linux/clk.h
@@ -328,6 +328,15 @@ long clk_round_rate(struct clk *clk, unsigned long rate);
int clk_set_rate(struct clk *clk, unsigned long rate);
/**
+ * clk_try_parent - check if a clock can be the parent clock source of another
+ * @clk: clock source
+ * @parent: parent clock source
+ *
+ * Returns success (0) or negative errno.
+ */
+int clk_try_parent(struct clk *clk, struct clk *parent);
+
+/**
* clk_set_parent - set the parent clock source for this clock
* @clk: clock source
* @parent: parent clock source
@@ -400,6 +409,11 @@ static inline long clk_round_rate(struct clk *clk, unsigned long rate)
return 0;
}
+static inline int clk_try_parent(struct clk *clk, struct clk *parent)
+{
+ return 0;
+}
+
static inline int clk_set_parent(struct clk *clk, struct clk *parent)
{
return 0;
--
2.1.3
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