clk: test: Add a determine_rate hook

The single parent clock in our kunit tests implements a mux with a
set_parent hook, but doesn't provide a determine_rate implementation.

This is not entirely unexpected, since its whole purpose it to have a
single parent. When determine_rate is missing, and since
CLK_SET_RATE_PARENT is set for all its instances, the default behaviour
of the framework will be to forward it to the current parent.

This is totally fine as far as the tests are concerned, but we'll start
to mandate a determine_rate implementation when set_parent is set, so
let's fill it with __clk_mux_determine_rate() which will have the same
behavior.
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/20221018-clk-range-checks-fixes-v4-7-971d5077e7d2@cerno.techSigned-off-by: Stephen Boyd <sboyd@kernel.org>

drivers/clk/clk_test.c

@@ -104,6 +104,23 @@ static const struct clk_ops clk_dummy_minimize_rate_ops = {
 };
 
 static const struct clk_ops clk_dummy_single_parent_ops = {
+	/*
+	 * FIXME: Even though we should probably be able to use
+	 * __clk_mux_determine_rate() here, if we use it and call
+	 * clk_round_rate() or clk_set_rate() with a rate lower than
+	 * what all the parents can provide, it will return -EINVAL.
+	 *
+	 * This is due to the fact that it has the undocumented
+	 * behaviour to always pick up the closest rate higher than the
+	 * requested rate. If we get something lower, it thus considers
+	 * that it's not acceptable and will return an error.
+	 *
+	 * It's somewhat inconsistent and creates a weird threshold
+	 * between rates above the parent rate which would be rounded to
+	 * what the parent can provide, but rates below will simply
+	 * return an error.
+	 */
+	.determine_rate = __clk_mux_determine_rate_closest,
 	.set_parent = clk_dummy_single_set_parent,
 	.get_parent = clk_dummy_single_get_parent,
 };