clk: Allow late cache allocation for clk->parents

Parent clocks for muxes are cached in clk->parents to
avoid frequent lookups, however the cache allocation happens
only during clock registeration and later clk_set_parent()
assumes a cache space available and allocated.

This is not entirely true for platforms which do early clock
registerations wherein the cache allocation using kzalloc
could fail during clock registeration.

Allow cache allocation to happen later as part of clk_set_parent()
to help such cases and avoid crashes assuming a cache being
available.

While here also replace existing kmalloc() with kzalloc()
in the file.
Signed-off-by: Rajendra Nayak <rnayak@ti.com>
Signed-off-by: Mike Turquette <mturquette@linaro.org>
Cc: stable@kernel.org

drivers/clk/clk.c

@@ -999,7 +999,7 @@ static struct clk *__clk_init_parent(struct clk *clk)
 
 	if (!clk->parents)
 		clk->parents =
-			kmalloc((sizeof(struct clk*) * clk->num_parents),
+			kzalloc((sizeof(struct clk*) * clk->num_parents),
 					GFP_KERNEL);
 
 	if (!clk->parents)
@@ -1065,9 +1065,13 @@ static int __clk_set_parent(struct clk *clk, struct clk *parent)
 	old_parent = clk->parent;
 
 	/* find index of new parent clock using cached parent ptrs */
+	if (clk->parents)
 		for (i = 0; i < clk->num_parents; i++)
 			if (clk->parents[i] == parent)
 				break;
+	else
+		clk->parents = kzalloc((sizeof(struct clk*) * clk->num_parents),
+								GFP_KERNEL);
 
 	/*
 	 * find index of new parent clock using string name comparison
@@ -1076,6 +1080,7 @@ static int __clk_set_parent(struct clk *clk, struct clk *parent)
 	if (i == clk->num_parents)
 		for (i = 0; i < clk->num_parents; i++)
 			if (!strcmp(clk->parent_names[i], parent->name)) {
+				if (clk->parents)
 					clk->parents[i] = __clk_lookup(parent->name);
 				break;
 			}