linux-kernel - Re: [PATCH v2 2/3] clk: conf: Support assigned-clock-sscs

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Message-ID: <aLeEFzXkPog_dt2B@x1>
Date: Tue, 2 Sep 2025 19:56:07 -0400
From: Brian Masney <bmasney@...hat.com>
To: Peng Fan <peng.fan@....com>
Cc: Michael Turquette <mturquette@...libre.com>,
	Stephen Boyd <sboyd@...nel.org>,
	Sudeep Holla <sudeep.holla@....com>,
	Cristian Marussi <cristian.marussi@....com>,
	Marco Felsch <m.felsch@...gutronix.de>,
	Dan Carpenter <dan.carpenter@...aro.org>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org,
	arm-scmi@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 2/3] clk: conf: Support assigned-clock-sscs

Hi Peng,

On Mon, Sep 01, 2025 at 11:51:46AM +0800, Peng Fan wrote:
> Parse the Spread Spectrum Configuration(SSC) from device tree and configure
> them before using the clock.
> 
> Each SSC is three u32 elements which means '<modfreq spreaddepth
> modmethod>', so assigned-clock-sscs is an array of multiple three u32
> elements.
> 
> Signed-off-by: Peng Fan <peng.fan@....com>

Stephen has also been asking for kunit tests to be added for new
functionality in the clk core. There's already one kunit test that
calls of_clk_set_defaults(). I attached a very rough draft of a patch
showing that it'd be possible to mock this up in a test with what's
already there. I set a log statement with the configuration from
device tree:

test_assigned_rate0: Spread Sprectrum Configuration: modfreq_hz=10000 spread_bp=3 method=1

You can run the kunit tests with:

./tools/testing/kunit/kunit.py run \
	--kunitconfig drivers/clk/.kunitconfig \
	--raw_output=all

Additionally, what do you think about making a dt-bindings include file
for CLK_SSC_CENTER_SPREAD + friends? Right now, the test illustrates
that we need to hardcode the number from the clk-provider.h file inside
the DTS.

Here's the patch and feel free to make it your own as you see fit.

Brian



diff --git a/drivers/clk/clk_test.c b/drivers/clk/clk_test.c
index a268d7b5d4cb..6cc3ad883b35 100644
--- a/drivers/clk/clk_test.c
+++ b/drivers/clk/clk_test.c
@@ -28,6 +28,7 @@ static const struct clk_ops empty_clk_ops = { };
 struct clk_dummy_context {
 	struct clk_hw hw;
 	unsigned long rate;
+	struct clk_spread_spectrum sscs;
 };
 
 static unsigned long clk_dummy_recalc_rate(struct clk_hw *hw,
@@ -83,6 +84,17 @@ static int clk_dummy_set_rate(struct clk_hw *hw,
 	return 0;
 }
 
+static int clk_dummy_set_spread_spectrum(struct clk_hw *hw,
+					 struct clk_spread_spectrum *conf)
+{
+	struct clk_dummy_context *ctx =
+		container_of(hw, struct clk_dummy_context, hw);
+
+	ctx->sscs = *conf;
+
+	return 0;
+}
+
 static int clk_dummy_single_set_parent(struct clk_hw *hw, u8 index)
 {
 	if (index >= clk_hw_get_num_parents(hw))
@@ -100,18 +112,21 @@ static const struct clk_ops clk_dummy_rate_ops = {
 	.recalc_rate = clk_dummy_recalc_rate,
 	.determine_rate = clk_dummy_determine_rate,
 	.set_rate = clk_dummy_set_rate,
+	.set_spread_spectrum = clk_dummy_set_spread_spectrum,
 };
 
 static const struct clk_ops clk_dummy_maximize_rate_ops = {
 	.recalc_rate = clk_dummy_recalc_rate,
 	.determine_rate = clk_dummy_maximize_rate,
 	.set_rate = clk_dummy_set_rate,
+	.set_spread_spectrum = clk_dummy_set_spread_spectrum,
 };
 
 static const struct clk_ops clk_dummy_minimize_rate_ops = {
 	.recalc_rate = clk_dummy_recalc_rate,
 	.determine_rate = clk_dummy_minimize_rate,
 	.set_rate = clk_dummy_set_rate,
+	.set_spread_spectrum = clk_dummy_set_spread_spectrum,
 };
 
 static const struct clk_ops clk_dummy_single_parent_ops = {
@@ -3192,7 +3207,13 @@ static int clk_assigned_rates_test_init(struct kunit *test)
 			consumer = of_find_compatible_node(NULL, NULL, "test,clk-consumer"));
 		of_node_put_kunit(test, consumer);
 
+		// Here's an example of a test that shows where
+		// of_clk_set_defaults() is called for the consumer.
 		KUNIT_ASSERT_EQ(test, 0, of_clk_set_defaults(consumer, false));
+		pr_crit("%s: Spread Sprectrum Configuration: modfreq_hz=%u spread_bp=%u method=%u\n",
+			clk_hw_get_name(&ctx->clk0.hw), ctx->clk0.sscs.modfreq_hz,
+			ctx->clk0.sscs.spread_bp, ctx->clk0.sscs.method);
+
 	}
 
 	return 0;
diff --git a/drivers/clk/kunit_clk_assigned_rates_one_consumer.dtso b/drivers/clk/kunit_clk_assigned_rates_one_consumer.dtso
index a41dca806318..a157a316a10d 100644
--- a/drivers/clk/kunit_clk_assigned_rates_one_consumer.dtso
+++ b/drivers/clk/kunit_clk_assigned_rates_one_consumer.dtso
@@ -14,5 +14,6 @@ kunit-clock-consumer {
 		compatible = "test,clk-consumer";
 		assigned-clocks = <&clk>;
 		assigned-clock-rates = <ASSIGNED_RATES_0_RATE>;
+		assigned-clock-sscs = <10000 3 1>;
 	};
 };