clk: Introduce clk_has_parent()
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@arm.linux.org.uk>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Reviewed-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Michael Turquette <mturquette@linaro.org>
diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index f4963b7..5272ad7 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -1652,6 +1652,36 @@
}
/**
+ * clk_has_parent - check if a clock is a possible parent for another
+ * @clk: clock source
+ * @parent: parent clock source
+ *
+ * This function can be used in drivers that need to check that a clock can be
+ * the parent of another without actually changing the parent.
+ *
+ * Returns true if @parent is a possible parent for @clk, false otherwise.
+ */
+bool clk_has_parent(struct clk *clk, struct clk *parent)
+{
+ unsigned int i;
+
+ /* NULL clocks should be nops, so return success if either is NULL. */
+ if (!clk || !parent)
+ return true;
+
+ /* Optimize for the case where the parent is already the parent. */
+ if (clk->parent == parent)
+ return true;
+
+ for (i = 0; i < clk->num_parents; i++)
+ if (strcmp(clk->parent_names[i], parent->name) == 0)
+ return true;
+
+ return false;
+}
+EXPORT_SYMBOL_GPL(clk_has_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