[PATCH v2 0/3] Fix clk-divider rates above 4.29 GHz on 64-bit

[PATCH v2 0/3] Fix clk-divider rates above 4.29 GHz on 64-bit

[Carlo Caione]

On 64-bit platforms, the clk-divider truncates requested rates above
4.29 GHz when computing a divisor. Fix it and add KUnit tests.

Sebastian Reichel fixed this in 2023 [1], but later versions moved to a
new generic macro and were never applied. Patch 1 builds on his v1 and
rounds up with (parent_rate - 1) / rate + 1, which does not overflow
with clk_round_rate(clk, ULONG_MAX). Patch 2 fixes a division by zero
found by the new tests.

[1] https://lore.kernel.org/linux-clk/20230519190522.194729-3-sebastian.reichel@collabora.com/

---
Changes in v2:
- Patch 1: round up with (parent_rate - 1) / rate + 1, as
  DIV64_U64_ROUND_UP() overflows with clk_round_rate(clk, ULONG_MAX)
  (Jerome, David)
- New patch 2: fix a division by zero in round-closest dividers
- Patch 3: also test the maximum rate (Brian) and rates above the parent
- Link to v1: https://patch.msgid.link/20261102-upstream-clk-divider-large-rates-v1-0-eb17035bfad2@baylibre.com

---
Carlo Caione (3):
      clk: divider: Fix the divisor for rates above 4.29 GHz
      clk: divider: Fix round-closest for rates above the parent rate
      clk: divider: test: Add tests for rates above 4.29 GHz

 drivers/clk/clk-divider.c      |  21 +++-
 drivers/clk/clk-divider_test.c | 244 ++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 260 insertions(+), 5 deletions(-)
---
base-commit: ab94dbf302331eed3679e262e1d8d1a73f308640
change-id: 20261102-upstream-clk-divider-large-rates-872467864e39

Best regards,
--  
Carlo Caione <ccaione@baylibre.com>

[PATCH v2 1/3] clk: divider: Fix the divisor for rates above 4.29 GHz

[Carlo Caione]

DIV_ROUND_UP_ULL() takes a 32-bit divisor, so on 64-bit platforms a
requested rate above 4.29 GHz is truncated. A divider fed by a 5.94 GHz
PLL then computes a divisor of 7, not 1, for 5.94 GHz.

Round up with (parent_rate - 1) / rate + 1 instead, building on an
earlier fix by Sebastian Reichel. It divides by the full rate and does
not overflow with clk_round_rate(clk, ULONG_MAX).

Fixes: 9556f9dad8f5 ("clk: divider: handle integer overflow when dividing large clock rates")
Suggested-by: Jerome Brunet <jbrunet@baylibre.com>
Suggested-by: David Laight <david.laight.linux@gmail.com>
Signed-off-by: Carlo Caione <ccaione@baylibre.com>
---
 drivers/clk/clk-divider.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/drivers/clk/clk-divider.c b/drivers/clk/clk-divider.c
index f68216c65d3d..c3f46f9ee451 100644
--- a/drivers/clk/clk-divider.c
+++ b/drivers/clk/clk-divider.c
@@ -223,11 +223,21 @@ static int _round_down_table(const struct clk_div_table *table, int div)
 	return down;
 }
 
+/*
+ * DIV_ROUND_UP() without the addition, which overflows for rates close to
+ * ULONG_MAX, as with clk_round_rate(clk, ULONG_MAX)
+ */
+static unsigned long _get_div_round_up(unsigned long parent_rate,
+				       unsigned long rate)
+{
+	return parent_rate ? (parent_rate - 1) / rate + 1 : 0;
+}
+
 static int _div_round_up(const struct clk_div_table *table,
 			 unsigned long parent_rate, unsigned long rate,
 			 unsigned long flags)
 {
-	int div = DIV_ROUND_UP_ULL((u64)parent_rate, rate);
+	int div = _get_div_round_up(parent_rate, rate);
 
 	if (flags & CLK_DIVIDER_POWER_OF_TWO)
 		div = __roundup_pow_of_two(div);
@@ -244,7 +254,7 @@ static int _div_round_closest(const struct clk_div_table *table,
 	int up, down;
 	unsigned long up_rate, down_rate;
 
-	up = DIV_ROUND_UP_ULL((u64)parent_rate, rate);
+	up = _get_div_round_up(parent_rate, rate);
 	down = parent_rate / rate;
 
 	if (flags & CLK_DIVIDER_POWER_OF_TWO) {
@@ -423,7 +433,7 @@ int divider_get_val(unsigned long rate, unsigned long parent_rate,
 {
 	unsigned int div, value;
 
-	div = DIV_ROUND_UP_ULL((u64)parent_rate, rate);
+	div = _get_div_round_up(parent_rate, rate);
 
 	if (!_is_valid_div(table, div, flags))
 		return -EINVAL;

-- 
2.56.0

[PATCH v2 2/3] clk: divider: Fix round-closest for rates above the parent rate

[Carlo Caione]

When the requested rate is above the parent rate, _div_round_closest()
computes a down divider of 0 and divides the parent rate by it. Asking a
CLK_DIVIDER_ROUND_CLOSEST divider without CLK_SET_RATE_PARENT for its
maximum rate with clk_round_rate(clk, ULONG_MAX) then traps on x86.

No divider goes above the parent rate, so the smallest one is the
closest. Return it before dividing.

Fixes: 26bac95aa88c ("clk: divider: fix selection of divider when rounding to closest")
Signed-off-by: Carlo Caione <ccaione@baylibre.com>
---
 drivers/clk/clk-divider.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/clk/clk-divider.c b/drivers/clk/clk-divider.c
index c3f46f9ee451..ed60fa9b04fa 100644
--- a/drivers/clk/clk-divider.c
+++ b/drivers/clk/clk-divider.c
@@ -254,6 +254,11 @@ static int _div_round_closest(const struct clk_div_table *table,
 	int up, down;
 	unsigned long up_rate, down_rate;
 
+	/* No divider goes above the parent rate: the smallest one is the closest */
+	if (rate >= parent_rate)
+		return table && !(flags & CLK_DIVIDER_POWER_OF_TWO) ?
+		       _get_table_mindiv(table) : 1;
+
 	up = _get_div_round_up(parent_rate, rate);
 	down = parent_rate / rate;
 

-- 
2.56.0

[PATCH v2 3/3] clk: divider: test: Add tests for rates above 4.29 GHz

[Carlo Caione]

On 64-bit platforms, the divider truncated rates above 4.29 GHz when
computing a divisor.

Add tests rounding and setting such rates on a divider with a 6 GHz
parent, one for each divisor computation, and rounding the maximum rate
(ULONG_MAX). They are skipped on 32-bit platforms, where rates cannot
exceed 4.29 GHz. Also test round-closest dividers above their parent
rate.

Signed-off-by: Carlo Caione <ccaione@baylibre.com>
---
 drivers/clk/clk-divider_test.c | 244 ++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 242 insertions(+), 2 deletions(-)

diff --git a/drivers/clk/clk-divider_test.c b/drivers/clk/clk-divider_test.c
index 8ee1614128d0..734cbdad55dd 100644
--- a/drivers/clk/clk-divider_test.c
+++ b/drivers/clk/clk-divider_test.c
@@ -1,16 +1,20 @@
 // SPDX-License-Identifier: GPL-2.0
 /*
- * KUnit tests for clk_divider_bestdiv()
+ * KUnit tests for clk divider
  */
+#include <kunit/clk.h>
 #include <kunit/test.h>
 #include <linux/clk.h>
 #include <linux/clk-provider.h>
+#include <linux/io.h>
 #include <linux/limits.h>
 #include <linux/units.h>
 
 #define PARENT_RATE_1GHZ	GIGA
 #define PARENT_RATE_2GHZ	(2 * GIGA)
 #define PARENT_RATE_4GHZ	(4 * GIGA)
+#define PARENT_RATE_6GHZ	(6 * GIGA)
+#define PARENT_RATE_10GHZ	(10 * GIGA)
 
 KUNIT_DEFINE_ACTION_WRAPPER(clk_hw_unregister_fixed_rate_wrapper,
 			    clk_hw_unregister_fixed_rate, struct clk_hw *);
@@ -147,7 +151,243 @@ static struct kunit_suite clk_divider_bestdiv_test_suite = {
 	.test_cases = clk_divider_bestdiv_test_cases,
 };
 
-kunit_test_suite(clk_divider_bestdiv_test_suite);
+/*
+ * Register a fixed-rate parent at @parent_rate and a 3-bit divider (/1 to
+ * /8) using @fake_reg as its register.
+ */
+static struct clk_hw *clk_divider_large_rate_init(struct kunit *test,
+						  u32 *fake_reg,
+						  unsigned long parent_rate,
+						  unsigned long flags,
+						  u8 div_flags)
+{
+	struct clk_hw *parent_hw, *div_hw;
+
+	if (BITS_PER_LONG < 64)
+		kunit_skip(test, "rates above 4.29 GHz need a 64-bit unsigned long");
+
+	parent_hw = clk_hw_register_fixed_rate(NULL, "large-rate-parent",
+					       NULL, 0, parent_rate);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, parent_hw);
+	KUNIT_ASSERT_EQ(test, 0,
+			kunit_add_action_or_reset(test, clk_hw_unregister_fixed_rate_wrapper,
+						  parent_hw));
+
+	div_hw = clk_hw_register_divider(NULL, "large-rate-div",
+					 "large-rate-parent", flags,
+					 (void __iomem __force *)fake_reg,
+					 0, 3, div_flags, NULL);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, div_hw);
+	KUNIT_ASSERT_EQ(test, 0,
+			kunit_add_action_or_reset(test, clk_hw_unregister_divider_wrapper,
+						  div_hw));
+
+	return div_hw;
+}
+
+/*
+ * Test that rounding a rate above 4.29 GHz computes the divisor from the
+ * full rate: the parent rate needs /1.
+ */
+static void clk_divider_large_rate_round_up(struct kunit *test)
+{
+	struct clk_hw *div_hw;
+	u32 *fake_reg;
+
+	fake_reg = kunit_kzalloc(test, sizeof(*fake_reg), GFP_KERNEL);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, fake_reg);
+
+	div_hw = clk_divider_large_rate_init(test, fake_reg, PARENT_RATE_6GHZ,
+					     0, 0);
+
+	KUNIT_EXPECT_EQ(test, clk_hw_round_rate(div_hw, PARENT_RATE_6GHZ),
+			PARENT_RATE_6GHZ);
+}
+
+/*
+ * Same with CLK_DIVIDER_ROUND_CLOSEST: 4.4 GHz is closer to 3 GHz (/2) than
+ * to 6 GHz (/1).
+ */
+static void clk_divider_large_rate_round_closest(struct kunit *test)
+{
+	struct clk_hw *div_hw;
+	u32 *fake_reg;
+
+	fake_reg = kunit_kzalloc(test, sizeof(*fake_reg), GFP_KERNEL);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, fake_reg);
+
+	div_hw = clk_divider_large_rate_init(test, fake_reg, PARENT_RATE_6GHZ,
+					     0, CLK_DIVIDER_ROUND_CLOSEST);
+
+	KUNIT_EXPECT_EQ(test, clk_hw_round_rate(div_hw, 4400 * MEGA),
+			PARENT_RATE_6GHZ / 2);
+}
+
+/*
+ * Test that setting a rate above 4.29 GHz programs the right divisor.
+ * With CLK_SET_RATE_PARENT the rounding searches the parent rates and
+ * finds /1, so this only checks the set_rate path.
+ */
+static void clk_divider_large_rate_set_rate(struct kunit *test)
+{
+	struct clk_hw *div_hw;
+	struct clk *clk;
+	u32 *fake_reg;
+
+	fake_reg = kunit_kzalloc(test, sizeof(*fake_reg), GFP_KERNEL);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, fake_reg);
+
+	/* Start from /2 */
+	writel(1, (void __iomem __force *)fake_reg);
+
+	div_hw = clk_divider_large_rate_init(test, fake_reg, PARENT_RATE_6GHZ,
+					     CLK_SET_RATE_PARENT, 0);
+	clk = clk_hw_get_clk_kunit(test, div_hw, NULL);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, clk);
+
+	KUNIT_ASSERT_EQ(test, clk_set_rate(clk, PARENT_RATE_6GHZ), 0);
+	KUNIT_EXPECT_EQ(test, clk_get_rate(clk), PARENT_RATE_6GHZ);
+	KUNIT_EXPECT_EQ(test, *fake_reg, 0);
+}
+
+/*
+ * Round ULONG_MAX, the usual way to ask for the maximum rate, on a divider
+ * with a @parent_rate parent: it must return the parent rate.
+ */
+static void clk_divider_large_rate_check_max(struct kunit *test,
+					     unsigned long parent_rate,
+					     u8 div_flags)
+{
+	struct clk_hw *div_hw;
+	u32 *fake_reg;
+
+	fake_reg = kunit_kzalloc(test, sizeof(*fake_reg), GFP_KERNEL);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, fake_reg);
+
+	div_hw = clk_divider_large_rate_init(test, fake_reg, parent_rate, 0,
+					     div_flags);
+
+	KUNIT_EXPECT_EQ(test, clk_hw_round_rate(div_hw, ULONG_MAX), parent_rate);
+}
+
+static void clk_divider_large_rate_round_max(struct kunit *test)
+{
+	clk_divider_large_rate_check_max(test, PARENT_RATE_6GHZ, 0);
+}
+
+/* Same with a parent more than twice the 32-bit limit */
+static void clk_divider_large_rate_round_max_10ghz(struct kunit *test)
+{
+	clk_divider_large_rate_check_max(test, PARENT_RATE_10GHZ, 0);
+}
+
+/* Same with CLK_DIVIDER_ROUND_CLOSEST */
+static void clk_divider_large_rate_round_max_closest(struct kunit *test)
+{
+	clk_divider_large_rate_check_max(test, PARENT_RATE_6GHZ,
+					 CLK_DIVIDER_ROUND_CLOSEST);
+}
+
+/* Same with CLK_DIVIDER_POWER_OF_TWO and a 1 GHz parent */
+static void clk_divider_large_rate_round_max_pow2(struct kunit *test)
+{
+	clk_divider_large_rate_check_max(test, PARENT_RATE_1GHZ,
+					 CLK_DIVIDER_POWER_OF_TWO);
+}
+
+static struct kunit_case clk_divider_large_rate_test_cases[] = {
+	KUNIT_CASE(clk_divider_large_rate_round_up),
+	KUNIT_CASE(clk_divider_large_rate_round_closest),
+	KUNIT_CASE(clk_divider_large_rate_set_rate),
+	KUNIT_CASE(clk_divider_large_rate_round_max),
+	KUNIT_CASE(clk_divider_large_rate_round_max_10ghz),
+	KUNIT_CASE(clk_divider_large_rate_round_max_closest),
+	KUNIT_CASE(clk_divider_large_rate_round_max_pow2),
+	{}
+};
+
+static struct kunit_suite clk_divider_large_rate_test_suite = {
+	.name = "clk_divider_large_rate",
+	.test_cases = clk_divider_large_rate_test_cases,
+};
+
+/*
+ * Register a 1 GHz fixed-rate parent and a round-closest 3-bit divider using
+ * @fake_reg as its register and @table, if not NULL, as its divider table.
+ */
+static struct clk_hw *clk_divider_above_parent_init(struct kunit *test,
+						    u32 *fake_reg,
+						    const struct clk_div_table *table)
+{
+	struct clk_hw *parent_hw, *div_hw;
+
+	parent_hw = clk_hw_register_fixed_rate(NULL, "above-parent-parent",
+					       NULL, 0, PARENT_RATE_1GHZ);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, parent_hw);
+	KUNIT_ASSERT_EQ(test, 0,
+			kunit_add_action_or_reset(test, clk_hw_unregister_fixed_rate_wrapper,
+						  parent_hw));
+
+	div_hw = clk_hw_register_divider_table(NULL, "above-parent-div",
+					       "above-parent-parent", 0,
+					       (void __iomem __force *)fake_reg,
+					       0, 3, CLK_DIVIDER_ROUND_CLOSEST,
+					       table, NULL);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, div_hw);
+	KUNIT_ASSERT_EQ(test, 0,
+			kunit_add_action_or_reset(test, clk_hw_unregister_divider_wrapper,
+						  div_hw));
+
+	return div_hw;
+}
+
+/*
+ * Test that a round-closest divider asked for more than its parent rate
+ * picks its smallest divider: /1.
+ */
+static void clk_divider_above_parent_round_closest(struct kunit *test)
+{
+	struct clk_hw *div_hw;
+	u32 *fake_reg;
+
+	fake_reg = kunit_kzalloc(test, sizeof(*fake_reg), GFP_KERNEL);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, fake_reg);
+
+	div_hw = clk_divider_above_parent_init(test, fake_reg, NULL);
+
+	KUNIT_EXPECT_EQ(test, clk_hw_round_rate(div_hw, PARENT_RATE_2GHZ),
+			PARENT_RATE_1GHZ);
+}
+
+/* Same with a divider table, whose smallest divider is /2 */
+static void clk_divider_above_parent_round_closest_table(struct kunit *test)
+{
+	struct clk_hw *div_hw;
+	u32 *fake_reg;
+
+	fake_reg = kunit_kzalloc(test, sizeof(*fake_reg), GFP_KERNEL);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, fake_reg);
+
+	div_hw = clk_divider_above_parent_init(test, fake_reg, bestdiv_table);
+
+	KUNIT_EXPECT_EQ(test, clk_hw_round_rate(div_hw, PARENT_RATE_2GHZ),
+			PARENT_RATE_1GHZ / 2);
+}
+
+static struct kunit_case clk_divider_above_parent_test_cases[] = {
+	KUNIT_CASE(clk_divider_above_parent_round_closest),
+	KUNIT_CASE(clk_divider_above_parent_round_closest_table),
+	{}
+};
+
+static struct kunit_suite clk_divider_above_parent_test_suite = {
+	.name = "clk_divider_above_parent",
+	.test_cases = clk_divider_above_parent_test_cases,
+};
+
+kunit_test_suites(&clk_divider_bestdiv_test_suite,
+		  &clk_divider_large_rate_test_suite,
+		  &clk_divider_above_parent_test_suite);
 
 MODULE_DESCRIPTION("KUnit tests for clk divider");
 MODULE_LICENSE("GPL");

-- 
2.56.0

Re: [PATCH v2 1/3] clk: divider: Fix the divisor for rates above 4.29 GHz

[Brian Masney]

Hi Carlo,

> DIV_ROUND_UP_ULL() takes a 32-bit divisor, so on 64-bit platforms a
> requested rate above 4.29 GHz is truncated. A divider fed by a 5.94 GHz
> PLL then computes a divisor of 7, not 1, for 5.94 GHz.
> 
> Round up with (parent_rate - 1) / rate + 1 instead, building on an
> earlier fix by Sebastian Reichel. It divides by the full rate and does
> not overflow with clk_round_rate(clk, ULONG_MAX).
> 
> Fixes: 9556f9dad8f5 ("clk: divider: handle integer overflow when dividing large clock rates")
> Suggested-by: Jerome Brunet <jbrunet@baylibre.com>
> Suggested-by: David Laight <david.laight.linux@gmail.com>
> Signed-off-by: Carlo Caione <ccaione@baylibre.com>
> ---
>  drivers/clk/clk-divider.c | 16 +++++++++++++---
>  1 file changed, 13 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/clk/clk-divider.c b/drivers/clk/clk-divider.c
> index f68216c65d3d..c3f46f9ee451 100644
> --- a/drivers/clk/clk-divider.c
> +++ b/drivers/clk/clk-divider.c
> @@ -223,11 +223,21 @@ static int _round_down_table(const struct clk_div_table *table, int div)
>  	return down;
>  }
>  
> +/*
> + * DIV_ROUND_UP() without the addition, which overflows for rates close to
> + * ULONG_MAX, as with clk_round_rate(clk, ULONG_MAX)
> + */
> +static unsigned long _get_div_round_up(unsigned long parent_rate,
> +				       unsigned long rate)
> +{
> +	return parent_rate ? (parent_rate - 1) / rate + 1 : 0;
> +}
> +
>  static int _div_round_up(const struct clk_div_table *table,
>  			 unsigned long parent_rate, unsigned long rate,
>  			 unsigned long flags)
>  {
> -	int div = DIV_ROUND_UP_ULL((u64)parent_rate, rate);
> +	int div = _get_div_round_up(parent_rate, rate);

_get_div_round_up() returns an unsigned long however it's downsized to
an int here.

Brian

-- 
Brian Masney <masneyb@kernel.org>

Re: [PATCH v2 1/3] clk: divider: Fix the divisor for rates above 4.29 GHz

[Carlo Caione]

On Thu, Nov 12, 2026 at 10:09:46 +0100, Brian Masney wrote:
> Hi Carlo,

Hi Brian,

> >  static int _div_round_up(const struct clk_div_table *table,
> >  			 unsigned long parent_rate, unsigned long rate,
> >  			 unsigned long flags)
> >  {
> > -	int div = DIV_ROUND_UP_ULL((u64)parent_rate, rate);
> > +	int div = _get_div_round_up(parent_rate, rate);
> 
> _get_div_round_up() returns an unsigned long however it's downsized to
> an int here.

Right, but wasn't also DIV_ROUND_UP_ULL() previously returning a u64
that was stored in the same int?

thanks,

--
Carlo Caione

Re: [PATCH v2 1/3] clk: divider: Fix the divisor for rates above 4.29 GHz

[Sebastian Reichel]

[-- Attachment #1: Type: text/plain, Size: 2617 bytes --]

Hi,

On Thu, Nov 12, 2026 at 10:36:59AM +0100, Carlo Caione wrote:
> DIV_ROUND_UP_ULL() takes a 32-bit divisor, so on 64-bit platforms a
> requested rate above 4.29 GHz is truncated. A divider fed by a 5.94 GHz
> PLL then computes a divisor of 7, not 1, for 5.94 GHz.
> 
> Round up with (parent_rate - 1) / rate + 1 instead, building on an
> earlier fix by Sebastian Reichel. It divides by the full rate and does
> not overflow with clk_round_rate(clk, ULONG_MAX).
> 
> Fixes: 9556f9dad8f5 ("clk: divider: handle integer overflow when dividing large clock rates")
> Suggested-by: Jerome Brunet <jbrunet@baylibre.com>
> Suggested-by: David Laight <david.laight.linux@gmail.com>
> Signed-off-by: Carlo Caione <ccaione@baylibre.com>
> ---

Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.com>

Greetings,

-- Sebastian

>  drivers/clk/clk-divider.c | 16 +++++++++++++---
>  1 file changed, 13 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/clk/clk-divider.c b/drivers/clk/clk-divider.c
> index f68216c65d3d..c3f46f9ee451 100644
> --- a/drivers/clk/clk-divider.c
> +++ b/drivers/clk/clk-divider.c
> @@ -223,11 +223,21 @@ static int _round_down_table(const struct clk_div_table *table, int div)
>  	return down;
>  }
>  
> +/*
> + * DIV_ROUND_UP() without the addition, which overflows for rates close to
> + * ULONG_MAX, as with clk_round_rate(clk, ULONG_MAX)
> + */
> +static unsigned long _get_div_round_up(unsigned long parent_rate,
> +				       unsigned long rate)
> +{
> +	return parent_rate ? (parent_rate - 1) / rate + 1 : 0;
> +}
> +
>  static int _div_round_up(const struct clk_div_table *table,
>  			 unsigned long parent_rate, unsigned long rate,
>  			 unsigned long flags)
>  {
> -	int div = DIV_ROUND_UP_ULL((u64)parent_rate, rate);
> +	int div = _get_div_round_up(parent_rate, rate);
>  
>  	if (flags & CLK_DIVIDER_POWER_OF_TWO)
>  		div = __roundup_pow_of_two(div);
> @@ -244,7 +254,7 @@ static int _div_round_closest(const struct clk_div_table *table,
>  	int up, down;
>  	unsigned long up_rate, down_rate;
>  
> -	up = DIV_ROUND_UP_ULL((u64)parent_rate, rate);
> +	up = _get_div_round_up(parent_rate, rate);
>  	down = parent_rate / rate;
>  
>  	if (flags & CLK_DIVIDER_POWER_OF_TWO) {
> @@ -423,7 +433,7 @@ int divider_get_val(unsigned long rate, unsigned long parent_rate,
>  {
>  	unsigned int div, value;
>  
> -	div = DIV_ROUND_UP_ULL((u64)parent_rate, rate);
> +	div = _get_div_round_up(parent_rate, rate);
>  
>  	if (!_is_valid_div(table, div, flags))
>  		return -EINVAL;
> 
> -- 
> 2.56.0
> 

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Re: [PATCH v2 1/3] clk: divider: Fix the divisor for rates above 4.29 GHz

[Sebastian Reichel]

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Hi,

On Thu, Nov 12, 2026 at 04:29:55PM +0100, Carlo Caione wrote:
> On Thu, Nov 12, 2026 at 10:09:46 +0100, Brian Masney wrote:
> > Hi Carlo,
> 
> Hi Brian,
> 
> > >  static int _div_round_up(const struct clk_div_table *table,
> > >  			 unsigned long parent_rate, unsigned long rate,
> > >  			 unsigned long flags)
> > >  {
> > > -	int div = DIV_ROUND_UP_ULL((u64)parent_rate, rate);
> > > +	int div = _get_div_round_up(parent_rate, rate);
> > 
> > _get_div_round_up() returns an unsigned long however it's downsized to
> > an int here.
> 
> Right, but wasn't also DIV_ROUND_UP_ULL() previously returning a u64
> that was stored in the same int?

I would also argue, that this is a separate fix. Looking at the code
involved it goes all the way down to this incorrectly using int for
a clock rate:

/*
 * ...
 * @determine_rate: Given a target rate as input, returns the closest rate
 *		actually supported by the clock, and optionally the parent clock
 *		that should be used to provide the clock rate.
 * ...
 */
struct clk_ops {
    ...
    int (*determine_rate)(struct clk_hw *hw,
                          struct clk_rate_request *req);
    ...
}

Fixing that will be a bigger task.

Greetings,

-- Sebastian

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Re: [PATCH v2 2/3] clk: divider: Fix round-closest for rates above the parent rate

[Sebastian Reichel]

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Hi,

On Thu, Nov 12, 2026 at 10:37:00AM +0100, Carlo Caione wrote:
> When the requested rate is above the parent rate, _div_round_closest()
> computes a down divider of 0 and divides the parent rate by it. Asking a
> CLK_DIVIDER_ROUND_CLOSEST divider without CLK_SET_RATE_PARENT for its
> maximum rate with clk_round_rate(clk, ULONG_MAX) then traps on x86.
> 
> No divider goes above the parent rate, so the smallest one is the
> closest. Return it before dividing.
> 
> Fixes: 26bac95aa88c ("clk: divider: fix selection of divider when rounding to closest")
> Signed-off-by: Carlo Caione <ccaione@baylibre.com>
> ---

Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.com>

Greetings,

-- Sebastian

>  drivers/clk/clk-divider.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/clk/clk-divider.c b/drivers/clk/clk-divider.c
> index c3f46f9ee451..ed60fa9b04fa 100644
> --- a/drivers/clk/clk-divider.c
> +++ b/drivers/clk/clk-divider.c
> @@ -254,6 +254,11 @@ static int _div_round_closest(const struct clk_div_table *table,
>  	int up, down;
>  	unsigned long up_rate, down_rate;
>  
> +	/* No divider goes above the parent rate: the smallest one is the closest */
> +	if (rate >= parent_rate)
> +		return table && !(flags & CLK_DIVIDER_POWER_OF_TWO) ?
> +		       _get_table_mindiv(table) : 1;
> +
>  	up = _get_div_round_up(parent_rate, rate);
>  	down = parent_rate / rate;
>  
> 
> -- 
> 2.56.0
> 

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