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Commit 858d5881 authored by Masahiro Yamada's avatar Masahiro Yamada Committed by Stephen Boyd
Browse files

clk: avoid circular clock topology 



Currently, clk_register() never checks a circular parent looping,
but clock providers could register such an insane clock topology.
For example, "clk_a" could have "clk_b" as a parent, and vice versa.
In this case, clk_core_reparent() creates a circular parent list
and __clk_recalc_accuracies() calls itself recursively forever.

The core infrastructure should be kind enough to bail out, showing
an appropriate error message in such a case.  This helps to easily
find a bug in clock providers.  (uh, I made such a silly mistake
when I was implementing my clock providers first.  I was upset
because the kernel did not respond, without any error message.)

This commit adds a new helper function, __clk_is_ancestor().  It
returns true if the second argument is a possible ancestor of the
first one.  If a clock core is a possible ancestor of itself, it
would make a loop when it were registered.  That should be detected
as an error.

Signed-off-by: default avatarMasahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: default avatarVladimir Zapolskiy <vz@mleia.com>
Signed-off-by: default avatarStephen Boyd <sboyd@codeaurora.org>
parent 5146e0b0

drivers/clk/clk.c

+40 −0
Original line number Diff line number Diff line
@@ -2252,6 +2252,38 @@ static inline void clk_debug_unregister(struct clk_core *core) 
}

#endif



/**

 * __clk_is_ancestor - check if a clk_core is a possible ancestor of another

 * @core: clock core

 * @ancestor: ancestor clock core

 *

 * Returns true if there is a possibility that @ancestor can be an ancestor

 * of @core, false otherwise.

 *

 * This function can be used against @core or @ancestor that has not been

 * registered yet.

 */

static bool __clk_is_ancestor(struct clk_core *core, struct clk_core *ancestor)

{

	struct clk_core *parent;

	int i;



	for (i = 0; i < core->num_parents; i++) {

		parent = clk_core_get_parent_by_index(core, i);

		/*

		 * If ancestor has not been added to clk_{root,orphan}_list

		 * yet, clk_core_lookup() cannot find it.  If parent is NULL,

		 * compare the name strings, too.

		 */

		if ((parent && (parent == ancestor ||

				__clk_is_ancestor(parent, ancestor))) ||

		    (!parent && !strcmp(core->parent_names[i], ancestor->name)))

			return true;

	}



	return false;

}



/**

 * __clk_core_init - initialize the data structures in a struct clk_core

 * @core:	clk_core being initialized
@@ -2317,6 +2349,14 @@ static int __clk_core_init(struct clk_core *core) 
				"%s: invalid NULL in %s's .parent_names\n",

				__func__, core->name);



	/* If core is an ancestor of itself, it would make a loop. */

	if (__clk_is_ancestor(core, core)) {

		pr_err("%s: %s would create circular parent\n", __func__,

		       core->name);

		ret = -EINVAL;

		goto out;

	}



	core->parent = __clk_init_parent(core);



	/*