[PATCH v4 0/2] clk: fractional-divider: Improve approximation when zero based and export

[PATCH v4 0/2] clk: fractional-divider: Improve approximation when zero based and export

[Frank Oltmanns]

The fractional divider approximation does not utilize the full available
range for clocks that are flagged CLK_FRAC_DIVIDER_ZERO_BASED. This
patchset aims to fix that.

It also adds test cases for the edge cases of fractional divider clocks
with and without the CLK_FRAC_DIVIDER_ZERO_BASED flag to highlight the
changes.

Finally, it also exports clk_fractional_divider_general_approximation so
that the test cases (but also other users like rockchip clk driver) can
be compiled as a module.

Unfortunately, I have no boards to test this patch. So all we have are
the unit tests. It seems the only user of this flag in mainline is
drivers/clk/imx/clk-composite-7ulp.c, therefore I'm cc-ing
get_maintainers.pl --git-blame -f drivers/clk/imx/clk-composite-7ulp.c
in the hopes of a wider audience.

Thank you for considering this contribution,
  Frank

V3: https://lore.kernel.org/all/20230614185521.477924-1-frank@oltmanns.dev/
V2: https://lore.kernel.org/lkml/20230613083626.227476-1-frank@oltmanns.dev/
V1: https://lore.kernel.org/lkml/20230529133433.56215-1-frank@oltmanns.dev/

Changes in V4 (since V3):
 - Export clk_fractional_divider_general_approximation so that users
   (e.g., the testcases) can be compiled as modules.
 - Change test cases so that they test
   clk_fractional_divider_general_approximation again (like in V2)
   instead of clk_fd_round_rate (like in V3), but keeping the structure
   of V3 with separate file and individual test cases for each edge
   case.

Changes in V3 (since V2):
 - Completely reworked the test cases
   - Moved tests to separate file as per Stephen's request
   - Move each edge case into their individual test case as per
     Stephen's request
   - Test clk_fd_round_rate instead of
     clk_fractional_divider_general_approximation as testing the latter
     broke builds

Changes in V2 (since V1):
 - Added test case as requested by Stephen Boyd
 - Fixed commit message as the Cc: was missing a closing bracket, so that the
   original mail unfortunately did not go out to A. s. Dong.

Frank Oltmanns (2):
  clk: fractional-divider: Improve approximation when zero based and
    export
  clk: fractional-divider: tests: Add test suite for edge cases

 drivers/clk/.kunitconfig                  |   1 +
 drivers/clk/Kconfig                       |   7 +
 drivers/clk/Makefile                      |   1 +
 drivers/clk/clk-fractional-divider.c      |  27 +++-
 drivers/clk/clk-fractional-divider_test.c | 161 ++++++++++++++++++++++
 5 files changed, 190 insertions(+), 7 deletions(-)
 create mode 100644 drivers/clk/clk-fractional-divider_test.c

-- 
2.41.0


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[PATCH v4 1/2] clk: fractional-divider: Improve approximation when zero based and export

[Frank Oltmanns]

Consider the CLK_FRAC_DIVIDER_ZERO_BASED flag when finding the best
approximation for m and n. By doing so, increase the range of valid
values for the numerator and denominator by 1.

Furthermore, export the approximation function so that users of this
function can be compiled as modules.

Cc: A.s. Dong <aisheng.dong@nxp.com>
Signed-off-by: Frank Oltmanns <frank@oltmanns.dev>
---
 drivers/clk/clk-fractional-divider.c | 27 ++++++++++++++++++++-------
 1 file changed, 20 insertions(+), 7 deletions(-)

diff --git a/drivers/clk/clk-fractional-divider.c b/drivers/clk/clk-fractional-divider.c
index 479297763e70..5067e067e906 100644
--- a/drivers/clk/clk-fractional-divider.c
+++ b/drivers/clk/clk-fractional-divider.c
@@ -123,6 +123,7 @@ void clk_fractional_divider_general_approximation(struct clk_hw *hw,
 						  unsigned long *m, unsigned long *n)
 {
 	struct clk_fractional_divider *fd = to_clk_fd(hw);
+	unsigned long max_m, max_n;
 
 	/*
 	 * Get rate closer to *parent_rate to guarantee there is no overflow
@@ -138,10 +139,17 @@ void clk_fractional_divider_general_approximation(struct clk_hw *hw,
 			rate <<= scale - fd->nwidth;
 	}
 
-	rational_best_approximation(rate, *parent_rate,
-			GENMASK(fd->mwidth - 1, 0), GENMASK(fd->nwidth - 1, 0),
-			m, n);
+	if (fd->flags & CLK_FRAC_DIVIDER_ZERO_BASED) {
+		max_m = 1 << fd->mwidth;
+		max_n = 1 << fd->nwidth;
+	} else {
+		max_m = GENMASK(fd->mwidth - 1, 0);
+		max_n = GENMASK(fd->nwidth - 1, 0);
+	}
+
+	rational_best_approximation(rate, *parent_rate, max_m, max_n, m, n);
 }
+EXPORT_SYMBOL_GPL(clk_fractional_divider_general_approximation);
 
 static long clk_fd_round_rate(struct clk_hw *hw, unsigned long rate,
 			      unsigned long *parent_rate)
@@ -169,13 +177,18 @@ static int clk_fd_set_rate(struct clk_hw *hw, unsigned long rate,
 {
 	struct clk_fractional_divider *fd = to_clk_fd(hw);
 	unsigned long flags = 0;
-	unsigned long m, n;
+	unsigned long m, n, max_m, max_n;
 	u32 mmask, nmask;
 	u32 val;
 
-	rational_best_approximation(rate, parent_rate,
-			GENMASK(fd->mwidth - 1, 0), GENMASK(fd->nwidth - 1, 0),
-			&m, &n);
+	if (fd->flags & CLK_FRAC_DIVIDER_ZERO_BASED) {
+		max_m = 1 << fd->mwidth;
+		max_n = 1 << fd->nwidth;
+	} else {
+		max_m = GENMASK(fd->mwidth - 1, 0);
+		max_n = GENMASK(fd->nwidth - 1, 0);
+	}
+	rational_best_approximation(rate, parent_rate, max_m, max_n, &m, &n);
 
 	if (fd->flags & CLK_FRAC_DIVIDER_ZERO_BASED) {
 		m--;
-- 
2.41.0


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[PATCH v4 2/2] clk: fractional-divider: tests: Add test suite for edge cases

[Frank Oltmanns]

In light of the recent discovery that the fractional divisor
approximation does not utilize the full available range for clocks that
are flagged CLK_FRAC_DIVIDER_ZERO_BASED [1], implement tests for the
edge cases of this clock type.

Signed-off-by: Frank Oltmanns <frank@oltmanns.dev>
Link: https://lore.kernel.org/lkml/20230529133433.56215-1-frank@oltmanns.dev [1]
---
Please note: I get two checkpatch warnings for this patch:
 - Concerning the help text in Kconfig.
 - Regarding the file being added, asking if MAINTAINERS needs updating.

Both the help text as well as the MAINTAINERS file seem fine to me.

As expected, when the tests are run *without* PATCH 1, the two "zero
based" test cases fail:

================= clk-fd-test (4 subtests) =================
[PASSED] clk_fd_test_approximation_max_denominator
[PASSED] clk_fd_test_approximation_max_numerator
# clk_fd_test_approximation_max_denominator_zero_based: EXPECTATION FAILED at drivers/clk/clk-fractional-divider_test.c:107
Expected n == max_n, but
    n == 7 (0x7)
    max_n == 8 (0x8)
[FAILED] clk_fd_test_approximation_max_denominator_zero_based
# clk_fd_test_approximation_max_numerator_zero_based: EXPECTATION FAILED at drivers/clk/clk-fractional-divider_test.c:138
Expected m == max_m, but
    m == 7 (0x7)
    max_m == 8 (0x8)
[FAILED] clk_fd_test_approximation_max_numerator_zero_based
# clk-fd-test: pass:2 fail:2 skip:0 total:4
# Totals: pass:2 fail:2 skip:0 total:4
=================== [FAILED] clk-fd-test ===================

Best regards,
  Frank

 drivers/clk/.kunitconfig                  |   1 +
 drivers/clk/Kconfig                       |   7 +
 drivers/clk/Makefile                      |   1 +
 drivers/clk/clk-fractional-divider_test.c | 161 ++++++++++++++++++++++
 4 files changed, 170 insertions(+)
 create mode 100644 drivers/clk/clk-fractional-divider_test.c

diff --git a/drivers/clk/Kconfig b/drivers/clk/Kconfig
index 016814e15536..3fbb40cb5551 100644
--- a/drivers/clk/Kconfig
+++ b/drivers/clk/Kconfig
@@ -513,4 +513,11 @@ config CLK_GATE_KUNIT_TEST
 	help
 	  Kunit test for the basic clk gate type.
 
+config CLK_FD_KUNIT_TEST
+	tristate "Basic fractional divider type Kunit test" if !KUNIT_ALL_TESTS
+	depends on KUNIT
+	default KUNIT_ALL_TESTS
+	help
+	  Kunit test for the clk-fractional-divider type.
+
 endif
diff --git a/drivers/clk/Makefile b/drivers/clk/Makefile
index 0aebef17edc6..9d2337c12dd1 100644
--- a/drivers/clk/Makefile
+++ b/drivers/clk/Makefile
@@ -12,6 +12,7 @@ obj-$(CONFIG_COMMON_CLK)	+= clk-multiplier.o
 obj-$(CONFIG_COMMON_CLK)	+= clk-mux.o
 obj-$(CONFIG_COMMON_CLK)	+= clk-composite.o
 obj-$(CONFIG_COMMON_CLK)	+= clk-fractional-divider.o
+obj-$(CONFIG_CLK_FD_KUNIT_TEST) += clk-fractional-divider_test.o
 obj-$(CONFIG_COMMON_CLK)	+= clk-gpio.o
 ifeq ($(CONFIG_OF), y)
 obj-$(CONFIG_COMMON_CLK)	+= clk-conf.o
diff --git a/drivers/clk/clk-fractional-divider_test.c b/drivers/clk/clk-fractional-divider_test.c
new file mode 100644
index 000000000000..30a776cf33c0
--- /dev/null
+++ b/drivers/clk/clk-fractional-divider_test.c
@@ -0,0 +1,161 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Kunit test for clock fractional divider
+ */
+#include <linux/clk.h>
+#include <linux/clk-provider.h>
+
+/* Needed for clk_hw_get_clk() */
+#include "clk.h"
+
+/* Needed for clk_fractional_divider_general_approximation */
+#include "clk-fractional-divider.h"
+
+#include <kunit/test.h>
+
+/*
+ * Test the maximum denominator case for fd clock without flags.
+ *
+ * Expect the highest possible denominator to be used in order to get as close as possible to the
+ * requested rate.
+ */
+static void clk_fd_test_approximation_max_denominator(struct kunit *test)
+{
+	struct clk_fractional_divider *fd;
+	struct clk_hw *hw;
+	unsigned long rate, parent_rate, m, n, max_m, max_n;
+
+	fd = kunit_kzalloc(test, sizeof(*fd), GFP_KERNEL);
+	KUNIT_ASSERT_NOT_NULL(test, fd);
+
+	fd->mwidth = 3;
+	max_m = 7;
+	fd->nwidth = 3;
+	max_n = 7;
+
+	hw = &fd->hw;
+
+	rate = 240000000;
+	parent_rate = (max_n + 1) * rate; /* so that it exceeds the maximum divisor */
+
+	clk_fractional_divider_general_approximation(hw, rate, &parent_rate, &m, &n);
+	KUNIT_EXPECT_EQ(test, parent_rate, (max_n + 1) * rate); /* parent remains unchanged */
+	KUNIT_EXPECT_EQ(test, m, 1);
+	KUNIT_EXPECT_EQ(test, n, max_n);
+}
+
+/*
+ * Test the maximum numerator case for fd clock without flags.
+ *
+ * Expect the highest possible numerator to be used in order to get as close as possible to the
+ * requested rate.
+ */
+static void clk_fd_test_approximation_max_numerator(struct kunit *test)
+{
+	struct clk_fractional_divider *fd;
+	struct clk_hw *hw;
+	unsigned long rate, parent_rate, m, n, max_m, max_n;
+
+	fd = kunit_kzalloc(test, sizeof(*fd), GFP_KERNEL);
+	KUNIT_ASSERT_NOT_NULL(test, fd);
+
+	fd->mwidth = 3;
+	max_m = 7;
+	fd->nwidth = 3;
+	max_n = 7;
+
+	hw = &fd->hw;
+
+	rate = 240000000;
+	parent_rate = rate / (max_m + 1); /* so that it exceeds the maximum numerator */
+
+	clk_fractional_divider_general_approximation(hw, rate, &parent_rate, &m, &n);
+	KUNIT_EXPECT_EQ(test, parent_rate, rate / (max_n + 1)); /* parent remains unchanged */
+	KUNIT_EXPECT_EQ(test, m, max_m);
+	KUNIT_EXPECT_EQ(test, n, 1);
+}
+
+/*
+ * Test the maximum denominator case for zero based fd clock.
+ *
+ * Expect the highest possible denominator to be used in order to get as close as possible to the
+ * requested rate.
+ */
+static void clk_fd_test_approximation_max_denominator_zero_based(struct kunit *test)
+{
+	struct clk_fractional_divider *fd;
+	struct clk_hw *hw;
+	unsigned long rate, parent_rate, m, n, max_m, max_n;
+
+	fd = kunit_kzalloc(test, sizeof(*fd), GFP_KERNEL);
+	KUNIT_ASSERT_NOT_NULL(test, fd);
+
+	fd->flags = CLK_FRAC_DIVIDER_ZERO_BASED;
+	fd->mwidth = 3;
+	max_m = 8;
+	fd->nwidth = 3;
+	max_n = 8;
+
+	hw = &fd->hw;
+
+	rate = 240000000;
+	parent_rate = (max_n + 1) * rate; /* so that it exceeds the maximum divisor */
+
+	clk_fractional_divider_general_approximation(hw, rate, &parent_rate, &m, &n);
+	KUNIT_EXPECT_EQ(test, parent_rate, (max_n + 1) * rate); /* parent remains unchanged */
+	KUNIT_EXPECT_EQ(test, m, 1);
+	KUNIT_EXPECT_EQ(test, n, max_n);
+}
+
+/*
+ * Test the maximum numerator case for zero based fd clock.
+ *
+ * Expect the highest possible numerator to be used in order to get as close as possible to the
+ * requested rate.
+ */
+static void clk_fd_test_approximation_max_numerator_zero_based(struct kunit *test)
+{
+	struct clk_fractional_divider *fd;
+	struct clk_hw *hw;
+	unsigned long rate, parent_rate, m, n, max_m, max_n;
+
+	fd = kunit_kzalloc(test, sizeof(*fd), GFP_KERNEL);
+	KUNIT_ASSERT_NOT_NULL(test, fd);
+
+	fd->flags = CLK_FRAC_DIVIDER_ZERO_BASED;
+	fd->mwidth = 3;
+	max_m = 8;
+	fd->nwidth = 3;
+	max_n = 8;
+
+	hw = &fd->hw;
+
+	rate = 240000000;
+	parent_rate = rate / (max_m + 1); /* so that it exceeds the maximum numerator */
+
+	clk_fractional_divider_general_approximation(hw, rate, &parent_rate, &m, &n);
+	KUNIT_EXPECT_EQ(test, parent_rate, rate / (max_n + 1)); /* parent remains unchanged */
+	KUNIT_EXPECT_EQ(test, m, max_m);
+	KUNIT_EXPECT_EQ(test, n, 1);
+}
+
+static struct kunit_case clk_fd_test_cases[] = {
+	KUNIT_CASE(clk_fd_test_approximation_max_denominator),
+	KUNIT_CASE(clk_fd_test_approximation_max_numerator),
+	KUNIT_CASE(clk_fd_test_approximation_max_denominator_zero_based),
+	KUNIT_CASE(clk_fd_test_approximation_max_numerator_zero_based),
+	{}
+};
+
+/*
+ * Test suite for a fractional divider clock.
+ */
+static struct kunit_suite clk_fd_test_suite = {
+	.name = "clk-fd-test",
+	.test_cases = clk_fd_test_cases,
+};
+
+kunit_test_suites(
+	&clk_fd_test_suite
+);
+MODULE_LICENSE("GPL");
-- 
2.41.0


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Re: [PATCH v4 2/2] clk: fractional-divider: tests: Add test suite for edge cases

[kernel test robot]

Hi Frank,

kernel test robot noticed the following build warnings:

[auto build test WARNING on clk/clk-next]
[also build test WARNING on linus/master v6.4-rc6 next-20230616]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Frank-Oltmanns/clk-fractional-divider-Improve-approximation-when-zero-based-and-export/20230617-183118
base:   https://git.kernel.org/pub/scm/linux/kernel/git/clk/linux.git clk-next
patch link:    https://lore.kernel.org/r/20230617102919.27564-3-frank%40oltmanns.dev
patch subject: [PATCH v4 2/2] clk: fractional-divider: tests: Add test suite for edge cases
config: arm-randconfig-r046-20230617 (https://download.01.org/0day-ci/archive/20230617/202306171912.PqJBpGMg-lkp@intel.com/config)
compiler: arm-linux-gnueabi-gcc (GCC) 12.3.0
reproduce: (https://download.01.org/0day-ci/archive/20230617/202306171912.PqJBpGMg-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202306171912.PqJBpGMg-lkp@intel.com/

All warnings (new ones prefixed by >>):

   drivers/clk/clk-fractional-divider_test.c: In function 'clk_fd_test_approximation_max_denominator':
>> drivers/clk/clk-fractional-divider_test.c:26:48: warning: variable 'max_m' set but not used [-Wunused-but-set-variable]
      26 |         unsigned long rate, parent_rate, m, n, max_m, max_n;
         |                                                ^~~~~
   drivers/clk/clk-fractional-divider_test.c: In function 'clk_fd_test_approximation_max_denominator_zero_based':
   drivers/clk/clk-fractional-divider_test.c:88:48: warning: variable 'max_m' set but not used [-Wunused-but-set-variable]
      88 |         unsigned long rate, parent_rate, m, n, max_m, max_n;
         |                                                ^~~~~


vim +/max_m +26 drivers/clk/clk-fractional-divider_test.c

    15	
    16	/*
    17	 * Test the maximum denominator case for fd clock without flags.
    18	 *
    19	 * Expect the highest possible denominator to be used in order to get as close as possible to the
    20	 * requested rate.
    21	 */
    22	static void clk_fd_test_approximation_max_denominator(struct kunit *test)
    23	{
    24		struct clk_fractional_divider *fd;
    25		struct clk_hw *hw;
  > 26		unsigned long rate, parent_rate, m, n, max_m, max_n;
    27	
    28		fd = kunit_kzalloc(test, sizeof(*fd), GFP_KERNEL);
    29		KUNIT_ASSERT_NOT_NULL(test, fd);
    30	
    31		fd->mwidth = 3;
    32		max_m = 7;
    33		fd->nwidth = 3;
    34		max_n = 7;
    35	
    36		hw = &fd->hw;
    37	
    38		rate = 240000000;
    39		parent_rate = (max_n + 1) * rate; /* so that it exceeds the maximum divisor */
    40	
    41		clk_fractional_divider_general_approximation(hw, rate, &parent_rate, &m, &n);
    42		KUNIT_EXPECT_EQ(test, parent_rate, (max_n + 1) * rate); /* parent remains unchanged */
    43		KUNIT_EXPECT_EQ(test, m, 1);
    44		KUNIT_EXPECT_EQ(test, n, max_n);
    45	}
    46	

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Re: [PATCH v4 2/2] clk: fractional-divider: tests: Add test suite for edge cases

[kernel test robot]

Hi Frank,

kernel test robot noticed the following build warnings:

[auto build test WARNING on clk/clk-next]
[also build test WARNING on linus/master v6.4-rc6 next-20230616]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Frank-Oltmanns/clk-fractional-divider-Improve-approximation-when-zero-based-and-export/20230617-183118
base:   https://git.kernel.org/pub/scm/linux/kernel/git/clk/linux.git clk-next
patch link:    https://lore.kernel.org/r/20230617102919.27564-3-frank%40oltmanns.dev
patch subject: [PATCH v4 2/2] clk: fractional-divider: tests: Add test suite for edge cases
config: hexagon-randconfig-r035-20230617 (https://download.01.org/0day-ci/archive/20230617/202306172036.EevtaVp6-lkp@intel.com/config)
compiler: clang version 17.0.0 (https://github.com/llvm/llvm-project.git 4a5ac14ee968ff0ad5d2cc1ffa0299048db4c88a)
reproduce: (https://download.01.org/0day-ci/archive/20230617/202306172036.EevtaVp6-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202306172036.EevtaVp6-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> drivers/clk/clk-fractional-divider_test.c:26:41: warning: variable 'max_m' set but not used [-Wunused-but-set-variable]
      26 |         unsigned long rate, parent_rate, m, n, max_m, max_n;
         |                                                ^
   drivers/clk/clk-fractional-divider_test.c:88:41: warning: variable 'max_m' set but not used [-Wunused-but-set-variable]
      88 |         unsigned long rate, parent_rate, m, n, max_m, max_n;
         |                                                ^
   2 warnings generated.


vim +/max_m +26 drivers/clk/clk-fractional-divider_test.c

    15	
    16	/*
    17	 * Test the maximum denominator case for fd clock without flags.
    18	 *
    19	 * Expect the highest possible denominator to be used in order to get as close as possible to the
    20	 * requested rate.
    21	 */
    22	static void clk_fd_test_approximation_max_denominator(struct kunit *test)
    23	{
    24		struct clk_fractional_divider *fd;
    25		struct clk_hw *hw;
  > 26		unsigned long rate, parent_rate, m, n, max_m, max_n;
    27	
    28		fd = kunit_kzalloc(test, sizeof(*fd), GFP_KERNEL);
    29		KUNIT_ASSERT_NOT_NULL(test, fd);
    30	
    31		fd->mwidth = 3;
    32		max_m = 7;
    33		fd->nwidth = 3;
    34		max_n = 7;
    35	
    36		hw = &fd->hw;
    37	
    38		rate = 240000000;
    39		parent_rate = (max_n + 1) * rate; /* so that it exceeds the maximum divisor */
    40	
    41		clk_fractional_divider_general_approximation(hw, rate, &parent_rate, &m, &n);
    42		KUNIT_EXPECT_EQ(test, parent_rate, (max_n + 1) * rate); /* parent remains unchanged */
    43		KUNIT_EXPECT_EQ(test, m, 1);
    44		KUNIT_EXPECT_EQ(test, n, max_n);
    45	}
    46	

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Re: [PATCH v4 2/2] clk: fractional-divider: tests: Add test suite for edge cases

[Frank Oltmanns]

On 2023-06-17 at 20:15:20 +0800, kernel test robot <lkp@intel.com> wrote:
> Hi Frank,
>
> kernel test robot noticed the following build warnings:
>
> [auto build test WARNING on clk/clk-next]
> [also build test WARNING on linus/master v6.4-rc6 next-20230616]
> [If your patch is applied to the wrong git tree, kindly drop us a note.
> And when submitting patch, we suggest to use '--base' as documented in
> https://git-scm.com/docs/git-format-patch#_base_tree_information]
>
> url:    https://github.com/intel-lab-lkp/linux/commits/Frank-Oltmanns/clk-fractional-divider-Improve-approximation-when-zero-based-and-export/20230617-183118
> base:   https://git.kernel.org/pub/scm/linux/kernel/git/clk/linux.git clk-next
> patch link:    https://lore.kernel.org/r/20230617102919.27564-3-frank%40oltmanns.dev
> patch subject: [PATCH v4 2/2] clk: fractional-divider: tests: Add test suite for edge cases
> config: hexagon-randconfig-r035-20230617 (https://download.01.org/0day-ci/archive/20230617/202306172036.EevtaVp6-lkp@intel.com/config)
> compiler: clang version 17.0.0 (https://github.com/llvm/llvm-project.git 4a5ac14ee968ff0ad5d2cc1ffa0299048db4c88a)
> reproduce: (https://download.01.org/0day-ci/archive/20230617/202306172036.EevtaVp6-lkp@intel.com/reproduce)
>
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@intel.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202306172036.EevtaVp6-lkp@intel.com/
>
> All warnings (new ones prefixed by >>):
>
>>> drivers/clk/clk-fractional-divider_test.c:26:41: warning: variable 'max_m' set but not used [-Wunused-but-set-variable]
>       26 |         unsigned long rate, parent_rate, m, n, max_m, max_n;
>          |                                                ^
>    drivers/clk/clk-fractional-divider_test.c:88:41: warning: variable 'max_m' set but not used [-Wunused-but-set-variable]
>       88 |         unsigned long rate, parent_rate, m, n, max_m, max_n;
>          |                                                ^
>    2 warnings generated.

Clang compiler warnings are fixed in version 5:
https://lore.kernel.org/all/20230617131041.18313-1-frank@oltmanns.dev/

>
>
> vim +/max_m +26 drivers/clk/clk-fractional-divider_test.c
>
>     15
>     16	/*
>     17	 * Test the maximum denominator case for fd clock without flags.
>     18	 *
>     19	 * Expect the highest possible denominator to be used in order to get as close as possible to the
>     20	 * requested rate.
>     21	 */
>     22	static void clk_fd_test_approximation_max_denominator(struct kunit *test)
>     23	{
>     24		struct clk_fractional_divider *fd;
>     25		struct clk_hw *hw;
>   > 26		unsigned long rate, parent_rate, m, n, max_m, max_n;
>     27
>     28		fd = kunit_kzalloc(test, sizeof(*fd), GFP_KERNEL);
>     29		KUNIT_ASSERT_NOT_NULL(test, fd);
>     30
>     31		fd->mwidth = 3;
>     32		max_m = 7;
>     33		fd->nwidth = 3;
>     34		max_n = 7;
>     35
>     36		hw = &fd->hw;
>     37
>     38		rate = 240000000;
>     39		parent_rate = (max_n + 1) * rate; /* so that it exceeds the maximum divisor */
>     40
>     41		clk_fractional_divider_general_approximation(hw, rate, &parent_rate, &m, &n);
>     42		KUNIT_EXPECT_EQ(test, parent_rate, (max_n + 1) * rate); /* parent remains unchanged */
>     43		KUNIT_EXPECT_EQ(test, m, 1);
>     44		KUNIT_EXPECT_EQ(test, n, max_n);
>     45	}
>     46

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