[PATCH 1/2] clk: Drive clk_leaf_mux_set_rate_parent test from clk_ops

Stephen Boyd
2023-09-12T17:55:38Z

Running this kunit test with lockdep enabled leads to warning splats
about calling clk provider APIs without the clk_prepare lock held. I
proposed adding a wrapper around these APIs to grab the prepare lock so
we can call them from anywhere, and Maxime implemented that approach[1],
but it didn't look great. That's because we had to make more kunit
testing APIs just to call code from a place that isn't a clk provider
when the prepare lock isn't held.

Instead of doing that, let's implement a determine_rate clk_op for a new
leaf clk that is the child of the existing leaf clk. We can call
__clk_determine_rate() on the existing leaf clk from there, and stash
away the clk_rate_request struct to check once the clk_op returns. Drive
that clk_op by calling clk_round_rate() to keep things similar to how it
was before (i.e. nothing actually changes rate, just the new rate is
determined). This silences the warning by driving the test from a
clk_op where we know the prepare lock is held.

While looking at this in more detail, it was determined that the code we
intended to test in commit 262ca38f4b6e ("clk: Stop forwarding
clk_rate_requests to the parent") wasn't actually tested. The call to
__clk_determine_rate() wasn't actually getting to the newly introduced
code under the CLK_SET_RATE_PARENT if condition in
clk_core_round_rate_nolock() because the parent clk (the mux) could
round rates. We introduce a new leaf and make sure the parent of that
clk has no clk_ops so that we can be certain that the
CLK_SET_RATE_PARENT condition in clk_core_round_rate_nolock() is
evaluated.

Reported-by: Guenter Roeck <linux@roeck-us.net>
Closes: https://lore.kernel.org/linux-clk/2b594e50-2bbf-4a2d-88e6-49fc39f3957a@roeck-us.net/
Reported-by: kernel test robot <yujie.liu@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202301310919.b9d56ee3-yujie.liu@intel.com
Cc: Maxime Ripard <mripard@kernel.org>
Link: https://lore.kernel.org/r/20230721-clk-fix-kunit-lockdep-v1-0-32cdba4c8fc1@kernel.org [1]
Fixes: 262ca38f4b6e ("clk: Stop forwarding clk_rate_requests to the parent")
Signed-off-by: Stephen Boyd <sboyd@kernel.org>
---
drivers/clk/clk_test.c | 65 +++++++++++++++++++++++++++++++-----------
1 file changed, 48 insertions(+), 17 deletions(-)

diff --git a/drivers/clk/clk_test.c b/drivers/clk/clk_test.c
index a154ec9d0111..43e85fc0b025 100644
--- a/drivers/clk/clk_test.c
+++ b/drivers/clk/clk_test.c
@@ -10,6 +10,8 @@

#include <kunit/test.h>

+static const struct clk_ops empty_clk_ops = { };
+
#define DUMMY_CLOCK_INIT_RATE (42 * 1000 * 1000)
#define DUMMY_CLOCK_RATE_1 (142 * 1000 * 1000)
#define DUMMY_CLOCK_RATE_2 (242 * 1000 * 1000)
@@ -2155,6 +2157,30 @@ static struct kunit_suite clk_range_minimize_test_suite = {
struct clk_leaf_mux_ctx {
struct clk_multiple_parent_ctx mux_ctx;
struct clk_hw hw;
+ struct clk_hw parent;
+ struct clk_rate_request *req;
+};
+
+static int clk_leaf_mux_determine_rate(struct clk_hw *hw, struct clk_rate_request *req)
+{
+ struct clk_leaf_mux_ctx *ctx = container_of(hw, struct clk_leaf_mux_ctx, hw);
+ int ret;
+ struct clk_rate_request *parent_req = ctx->req;
+
+ clk_hw_forward_rate_request(hw, req, req->best_parent_hw, parent_req, req->rate);
+ ret = __clk_determine_rate(req->best_parent_hw, parent_req);
+ if (ret)
+ return ret;
+
+ req->rate = parent_req->rate;
+
+ return 0;
+}
+
+static const struct clk_ops clk_leaf_mux_set_rate_parent_ops = {
+ .determine_rate = clk_leaf_mux_determine_rate,
+ .set_parent = clk_dummy_single_set_parent,
+ .get_parent = clk_dummy_single_get_parent,
};

static int
@@ -2193,8 +2219,14 @@ clk_leaf_mux_set_rate_parent_test_init(struct kunit *test)
if (ret)
return ret;

- ctx->hw.init = CLK_HW_INIT_HW("test-clock", &ctx->mux_ctx.hw,
- &clk_dummy_single_parent_ops,
+ ctx->parent.init = CLK_HW_INIT_HW("test-parent", &ctx->mux_ctx.hw,
+ &empty_clk_ops, CLK_SET_RATE_PARENT);
+ ret = clk_hw_register(NULL, &ctx->parent);
+ if (ret)
+ return ret;
+
+ ctx->hw.init = CLK_HW_INIT_HW("test-clock", &ctx->parent,
+ &clk_leaf_mux_set_rate_parent_ops,
CLK_SET_RATE_PARENT);
ret = clk_hw_register(NULL, &ctx->hw);
if (ret)
@@ -2208,32 +2240,31 @@ static void clk_leaf_mux_set_rate_parent_test_exit(struct kunit *test)
struct clk_leaf_mux_ctx *ctx = test->priv;

clk_hw_unregister(&ctx->hw);
+ clk_hw_unregister(&ctx->parent);
clk_hw_unregister(&ctx->mux_ctx.hw);
clk_hw_unregister(&ctx->mux_ctx.parents_ctx[0].hw);
clk_hw_unregister(&ctx->mux_ctx.parents_ctx[1].hw);
}

/*
- * Test that, for a clock that will forward any rate request to its
- * parent, the rate request structure returned by __clk_determine_rate
- * is sane and will be what we expect.
+ * Test that, for a clock that will forward any rate request to its parent, the
+ * rate request structure returned by __clk_determine_rate() is sane and
+ * doesn't have the clk_rate_request's best_parent_hw pointer point to the
+ * clk_hw passed into __clk_determine_rate(). See commit 262ca38f4b6e ("clk:
+ * Stop forwarding clk_rate_requests to the parent") for more background.
*/
-static void clk_leaf_mux_set_rate_parent_determine_rate(struct kunit *test)
+static void clk_leaf_mux_set_rate_parent__clk_determine_rate_proper_parent(struct kunit *test)
{
struct clk_leaf_mux_ctx *ctx = test->priv;
struct clk_hw *hw = &ctx->hw;
struct clk *clk = clk_hw_get_clk(hw, NULL);
struct clk_rate_request req;
unsigned long rate;
- int ret;

+ ctx->req = &req;
rate = clk_get_rate(clk);
KUNIT_ASSERT_EQ(test, rate, DUMMY_CLOCK_RATE_1);
-
- clk_hw_init_rate_request(hw, &req, DUMMY_CLOCK_RATE_2);
-
- ret = __clk_determine_rate(hw, &req);
- KUNIT_ASSERT_EQ(test, ret, 0);
+ KUNIT_ASSERT_EQ(test, DUMMY_CLOCK_RATE_2, clk_round_rate(clk, DUMMY_CLOCK_RATE_2));

KUNIT_EXPECT_EQ(test, req.rate, DUMMY_CLOCK_RATE_2);
KUNIT_EXPECT_EQ(test, req.best_parent_rate, DUMMY_CLOCK_RATE_2);
@@ -2243,15 +2274,15 @@ static void clk_leaf_mux_set_rate_parent_determine_rate(struct kunit *test)
}

static struct kunit_case clk_leaf_mux_set_rate_parent_test_cases[] = {
- KUNIT_CASE(clk_leaf_mux_set_rate_parent_determine_rate),
+ KUNIT_CASE(clk_leaf_mux_set_rate_parent__clk_determine_rate_proper_parent),
{}
};

/*
- * Test suite for a clock whose parent is a mux with multiple parents.
- * The leaf clock has CLK_SET_RATE_PARENT, and will forward rate
- * requests to the mux, which will then select which parent is the best
- * fit for a given rate.
+ * Test suite for a clock whose parent is a pass-through clk whose parent is a
+ * mux with multiple parents. The leaf and pass-through clocks have the
+ * CLK_SET_RATE_PARENT flag, and will forward rate requests to the mux, which
+ * will then select which parent is the best fit for a given rate.
*
* These tests exercise the behaviour of muxes, and the proper selection
* of parents.