clk: tests: Add tests for uncached clock

The clock framework supports clocks that can have their rate changed
without the kernel knowing about it using the CLK_GET_RATE_NOCACHE flag.

As its name suggests, this flag turns off the rate caching in the clock
framework, reading out the rate from the hardware any time we need to
read it.

Let's add a couple of tests to make sure it works as intended.

Tested-by: Alexander Stein <alexander.stein@ew.tq-group.com> # imx8mp
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com> # exynos4210, meson g12b
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/20220816112530.1837489-9-maxime@cerno.tech
Tested-by: Linux Kernel Functional Testing <lkft@linaro.org>
Tested-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>

drivers/clk/clk_test.c

@@ -270,6 +270,96 @@ static struct kunit_suite clk_test_suite = {
 	.test_cases = clk_test_cases,
 };
 
+static int clk_uncached_test_init(struct kunit *test)
+{
+	struct clk_dummy_context *ctx;
+	int ret;
+
+	ctx = kunit_kzalloc(test, sizeof(*ctx), GFP_KERNEL);
+	if (!ctx)
+		return -ENOMEM;
+	test->priv = ctx;
+
+	ctx->rate = DUMMY_CLOCK_INIT_RATE;
+	ctx->hw.init = CLK_HW_INIT_NO_PARENT("test-clk",
+					     &clk_dummy_rate_ops,
+					     CLK_GET_RATE_NOCACHE);
+
+	ret = clk_hw_register(NULL, &ctx->hw);
+	if (ret)
+		return ret;
+
+	return 0;
+}
+
+/*
+ * Test that for an uncached clock, the clock framework doesn't cache
+ * the rate and clk_get_rate() will return the underlying clock rate
+ * even if it changed.
+ */
+static void clk_test_uncached_get_rate(struct kunit *test)
+{
+	struct clk_dummy_context *ctx = test->priv;
+	struct clk_hw *hw = &ctx->hw;
+	struct clk *clk = clk_hw_get_clk(hw, NULL);
+	unsigned long rate;
+
+	rate = clk_get_rate(clk);
+	KUNIT_ASSERT_GT(test, rate, 0);
+	KUNIT_EXPECT_EQ(test, rate, DUMMY_CLOCK_INIT_RATE);
+
+	/* We change the rate behind the clock framework's back */
+	ctx->rate = DUMMY_CLOCK_RATE_1;
+	rate = clk_get_rate(clk);
+	KUNIT_ASSERT_GT(test, rate, 0);
+	KUNIT_EXPECT_EQ(test, rate, DUMMY_CLOCK_RATE_1);
+
+	clk_put(clk);
+}
+
+/*
+ * Test that for an uncached clock, clk_set_rate_range() will work
+ * properly if the rate hasn't changed.
+ */
+static void clk_test_uncached_set_range(struct kunit *test)
+{
+	struct clk_dummy_context *ctx = test->priv;
+	struct clk_hw *hw = &ctx->hw;
+	struct clk *clk = clk_hw_get_clk(hw, NULL);
+	unsigned long rate;
+
+	KUNIT_ASSERT_EQ(test,
+			clk_set_rate_range(clk,
+					   DUMMY_CLOCK_RATE_1,
+					   DUMMY_CLOCK_RATE_2),
+			0);
+
+	rate = clk_get_rate(clk);
+	KUNIT_ASSERT_GT(test, rate, 0);
+	KUNIT_EXPECT_GE(test, rate, DUMMY_CLOCK_RATE_1);
+	KUNIT_EXPECT_LE(test, rate, DUMMY_CLOCK_RATE_2);
+
+	clk_put(clk);
+}
+
+static struct kunit_case clk_uncached_test_cases[] = {
+	KUNIT_CASE(clk_test_uncached_get_rate),
+	KUNIT_CASE(clk_test_uncached_set_range),
+	{}
+};
+
+/*
+ * Test suite for a basic, uncached, rate clock, without any parent.
+ *
+ * These tests exercise the rate API with simple scenarios
+ */
+static struct kunit_suite clk_uncached_test_suite = {
+	.name = "clk-uncached-test",
+	.init = clk_uncached_test_init,
+	.exit = clk_test_exit,
+	.test_cases = clk_uncached_test_cases,
+};
+
 struct clk_single_parent_ctx {
 	struct clk_dummy_context parent_ctx;
 	struct clk_hw hw;
@@ -1077,6 +1167,7 @@ kunit_test_suites(
 	&clk_orphan_transparent_single_parent_test_suite,
 	&clk_range_test_suite,
 	&clk_range_maximize_test_suite,
-	&clk_range_minimize_test_suite
+	&clk_range_minimize_test_suite,
+	&clk_uncached_test_suite
 );
 MODULE_LICENSE("GPL v2");