[PATCH v2 2/2] clk: tests: Add tests for fractional divisor approximation

[Frank Oltmanns <frank@oltmanns.dev>]

In light of the recent discovery that the fractional divisor
approximation does not utilize the full available range for clocks that
are flagged CLK_FRAC_DIVIDER_ZERO_BASED, implement tests for the edge
cases of this clock type.

Signed-off-by: Frank Oltmanns <frank@oltmanns.dev>
Link: https://lore.kernel.org/lkml/20230529133433.56215-1-frank@oltmanns.dev
---
 drivers/clk/clk_test.c | 69 +++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 68 insertions(+), 1 deletion(-)

diff --git a/drivers/clk/clk_test.c b/drivers/clk/clk_test.c
index f9a5c2964c65..b247ba841cbd 100644
--- a/drivers/clk/clk_test.c
+++ b/drivers/clk/clk_test.c
@@ -8,6 +8,9 @@
 /* Needed for clk_hw_get_clk() */
 #include "clk.h"
 
+/* Needed for clk_fractional_divider_general_approximation */
+#include "clk-fractional-divider.h"
+
 #include <kunit/test.h>
 
 #define DUMMY_CLOCK_INIT_RATE	(42 * 1000 * 1000)
@@ -2394,6 +2397,69 @@ static struct kunit_suite clk_mux_notifier_test_suite = {
 	.test_cases = clk_mux_notifier_test_cases,
 };
 
+
+/*
+ * Test that clk_fractional_divider_general_approximation will work with the
+ * highest available numerator and denominator.
+ */
+static void clk_fd_test_round_rate_max_mn(struct kunit *test)
+{
+	struct clk_fractional_divider *fd;
+	struct clk_hw *hw;
+	unsigned long rate, parent_rate, m, n;
+
+	fd = kunit_kzalloc(test, sizeof(*fd), GFP_KERNEL);
+	KUNIT_ASSERT_NOT_NULL(test, fd);
+
+	fd->mwidth = 3;
+	fd->nwidth = 3;
+
+	hw = &fd->hw;
+
+	rate = DUMMY_CLOCK_RATE_1;
+
+	// Highest denominator, no flags
+	parent_rate = 10 * DUMMY_CLOCK_RATE_1;
+	clk_fractional_divider_general_approximation(hw, rate, &parent_rate, &m, &n);
+	KUNIT_EXPECT_EQ(test, m, 1);
+	KUNIT_EXPECT_EQ(test, n, 7);
+
+	// Highest numerator, no flags
+	parent_rate = DUMMY_CLOCK_RATE_1 / 10;
+	clk_fractional_divider_general_approximation(hw, rate, &parent_rate, &m, &n);
+	KUNIT_EXPECT_EQ(test, m, 7);
+	KUNIT_EXPECT_EQ(test, n, 1);
+
+	// Highest denominator, zero based
+	parent_rate = 10 * DUMMY_CLOCK_RATE_1;
+	fd->flags = CLK_FRAC_DIVIDER_ZERO_BASED;
+	clk_fractional_divider_general_approximation(hw, rate, &parent_rate, &m, &n);
+	KUNIT_EXPECT_EQ(test, m, 1);
+	KUNIT_EXPECT_EQ(test, n, 8);
+
+	// Highest numerator, zero based
+	parent_rate = DUMMY_CLOCK_RATE_1 / 10;
+	clk_fractional_divider_general_approximation(hw, rate, &parent_rate, &m, &n);
+	KUNIT_EXPECT_EQ(test, m, 8);
+	KUNIT_EXPECT_EQ(test, n, 1);
+}
+
+static struct kunit_case clk_fd_test_cases[] = {
+	KUNIT_CASE(clk_fd_test_round_rate_max_mn),
+	{}
+};
+
+/*
+ * Test suite for a fractional divider clock.
+ *
+ * These tests exercise the fractional divider API: clk_recalc_rate,
+ * clk_set_rate(), clk_round_rate().
+ */
+static struct kunit_suite clk_fd_test_suite = {
+	.name = "clk-fd-test",
+	.test_cases = clk_fd_test_cases,
+};
+
 kunit_test_suites(
 	&clk_leaf_mux_set_rate_parent_test_suite,
 	&clk_test_suite,
@@ -2406,6 +2472,7 @@ kunit_test_suites(
 	&clk_range_maximize_test_suite,
 	&clk_range_minimize_test_suite,
 	&clk_single_parent_mux_test_suite,
-	&clk_uncached_test_suite
+	&clk_uncached_test_suite,
+	&clk_fd_test_suite
 );
 MODULE_LICENSE("GPL v2");
-- 
2.41.0