[PATCH v13 3/4] clk: validate spread spectrum configuration

[Dario Binacchi <dario.binacchi@amarulasolutions.com>]

The spread spectrum configuration is passed to the provider's
set_spread_spectrum() callback without any validation, as clk-conf.c
only skips all-zero triplets from "assigned-clock-sscs". An invalid
device tree can hand providers a zero modulation frequency or a spread
ratio above 100%, and each provider would have to add the same checks
to protect e.g. divisions in its rate computations.

The KUnit test data for assigned-clock-sscs uses spread values of 30000
and 40000 permyriad (300% and 400%), which the new check rejects, as
reported by Sashiko, so fix them to 300 and 400 (3% and 4%). Also use
a realistic 6% value for the initial settings of the skip tests, for
consistency.

Fixes: c86814e70390 ("clk: Introduce clk_hw_set_spread_spectrum")
Reported-by: Sashiko <sashiko-bot@kernel.org>
Closes: https://lore.kernel.org/r/20260901155657.6A5981F00A3A@smtp.kernel.org
Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>

---

Changes in v13:
 - Fix the KUnit test data to realistic spread values.
 - Add the Reported-by/Closes tag for Sashiko.

 drivers/clk/clk.c                      | 14 ++++++++++++++
 drivers/clk/clk_test.c                 | 12 ++++++------
 drivers/clk/kunit_clk_assigned_rates.h |  4 ++--
 3 files changed, 22 insertions(+), 8 deletions(-)

diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index fef87167a60b..208caf60eeb5 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -2851,6 +2851,20 @@ int clk_hw_set_spread_spectrum(struct clk_hw *hw, const struct clk_spread_spectr
 	if (!hw)
 		return 0;
 
+	switch (ss_conf->method) {
+	case CLK_SPREAD_NO:
+		break;
+	case CLK_SPREAD_CENTER:
+	case CLK_SPREAD_UP:
+	case CLK_SPREAD_DOWN:
+		if (!ss_conf->modfreq_hz || !ss_conf->spread_bp ||
+		    ss_conf->spread_bp > 10000)
+			return -EINVAL;
+		break;
+	default:
+		return -EINVAL;
+	}
+
 	core = hw->core;
 
 	clk_prepare_lock();
diff --git a/drivers/clk/clk_test.c b/drivers/clk/clk_test.c
index 1c5c8b7c1f3c..21e62d68f87f 100644
--- a/drivers/clk/clk_test.c
+++ b/drivers/clk/clk_test.c
@@ -3526,7 +3526,7 @@ static const struct clk_assigned_rates_test_param clk_assigned_sscs_skips_test_p
 		 */
 		.desc = "provider missing assigned-clocks",
 		TEST_PARAM_OVERLAY(kunit_clk_assigned_sscs_without),
-		.sscs = {50000, 60000, 3},
+		.sscs = {50000, 600, 3},
 	},
 	{
 		/*
@@ -3535,7 +3535,7 @@ static const struct clk_assigned_rates_test_param clk_assigned_sscs_skips_test_p
 		 */
 		.desc = "consumer missing assigned-clocks",
 		TEST_PARAM_OVERLAY(kunit_clk_assigned_sscs_without_consumer),
-		.sscs = {50000, 60000, 3},
+		.sscs = {50000, 600, 3},
 		.consumer_test = true,
 	},
 	{
@@ -3545,7 +3545,7 @@ static const struct clk_assigned_rates_test_param clk_assigned_sscs_skips_test_p
 		 */
 		.desc = "provider assigned-clock-sscs of zero",
 		TEST_PARAM_OVERLAY(kunit_clk_assigned_sscs_zero),
-		.sscs = {50000, 60000, 3},
+		.sscs = {50000, 600, 3},
 	},
 	{
 		/*
@@ -3554,7 +3554,7 @@ static const struct clk_assigned_rates_test_param clk_assigned_sscs_skips_test_p
 		 */
 		.desc = "consumer assigned-clock-sscs of zero",
 		TEST_PARAM_OVERLAY(kunit_clk_assigned_sscs_zero_consumer),
-		.sscs = {50000, 60000, 3},
+		.sscs = {50000, 600, 3},
 		.consumer_test = true,
 	},
 	{
@@ -3564,7 +3564,7 @@ static const struct clk_assigned_rates_test_param clk_assigned_sscs_skips_test_p
 		 */
 		.desc = "provider assigned-clocks null phandle",
 		TEST_PARAM_OVERLAY(kunit_clk_assigned_sscs_null),
-		.sscs = {50000, 60000, 3},
+		.sscs = {50000, 600, 3},
 	},
 	{
 		/*
@@ -3573,7 +3573,7 @@ static const struct clk_assigned_rates_test_param clk_assigned_sscs_skips_test_p
 		 */
 		.desc = "consumer assigned-clocks null phandle",
 		TEST_PARAM_OVERLAY(kunit_clk_assigned_sscs_null_consumer),
-		.sscs = {50000, 60000, 3},
+		.sscs = {50000, 600, 3},
 		.consumer_test = true,
 	},
 };
diff --git a/drivers/clk/kunit_clk_assigned_rates.h b/drivers/clk/kunit_clk_assigned_rates.h
index d7ae5ec2d25b..c5d9f004ee81 100644
--- a/drivers/clk/kunit_clk_assigned_rates.h
+++ b/drivers/clk/kunit_clk_assigned_rates.h
@@ -9,10 +9,10 @@
 #define ASSIGNED_RATES_1_RATE		9700000
 
 #define ASSIGNED_SSCS_0_MODFREQ		10000
-#define ASSIGNED_SSCS_0_SPREAD		30000
+#define ASSIGNED_SSCS_0_SPREAD		300
 #define ASSIGNED_SSCS_0_METHOD		CLK_SSC_CENTER_SPREAD
 #define ASSIGNED_SSCS_1_MODFREQ		20000
-#define ASSIGNED_SSCS_1_SPREAD		40000
+#define ASSIGNED_SSCS_1_SPREAD		400
 #define ASSIGNED_SSCS_1_METHOD		CLK_SSC_UP_SPREAD
 
 #endif
-- 
2.43.0