[PATCH v2 2/2] clk: tests: Add tests for fractional divisor approximation

[Stephen Boyd]

Quoting Frank Oltmanns (2023-06-13 01:36:26)
> 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, implement tests for the edge
> cases of this clock type.
> 
> Signed-off-by: Frank Oltmanns <frank at oltmanns.dev>
> Link: https://lore.kernel.org/lkml/20230529133433.56215-1-frank@oltmanns.dev

What is the link for?

> ---
>  drivers/clk/clk_test.c | 69 +++++++++++++++++++++++++++++++++++++++++-

Please make a new file, drivers/clk/clk-fractional-divider_test.c
instead.

>  1 file changed, 68 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/clk/clk_test.c b/drivers/clk/clk_test.c
> index f9a5c2964c65..b247ba841cbd 100644
> --- a/drivers/clk/clk_test.c
> +++ b/drivers/clk/clk_test.c
> @@ -8,6 +8,9 @@
>  /* 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>
>  
>  #define DUMMY_CLOCK_INIT_RATE  (42 * 1000 * 1000)
> @@ -2394,6 +2397,69 @@ static struct kunit_suite clk_mux_notifier_test_suite = {
>         .test_cases = clk_mux_notifier_test_cases,
>  };
>  
> +
> +/*
> + * Test that clk_fractional_divider_general_approximation will work with the
> + * highest available numerator and denominator.
> + */
> +static void clk_fd_test_round_rate_max_mn(struct kunit *test)
> +{
> +       struct clk_fractional_divider *fd;
> +       struct clk_hw *hw;
> +       unsigned long rate, parent_rate, m, n;
> +
> +       fd = kunit_kzalloc(test, sizeof(*fd), GFP_KERNEL);
> +       KUNIT_ASSERT_NOT_NULL(test, fd);
> +
> +       fd->mwidth = 3;
> +       fd->nwidth = 3;
> +
> +       hw = &fd->hw;
> +
> +       rate = DUMMY_CLOCK_RATE_1;
> +
> +       // Highest denominator, no flags

Use /* this for comments */

> +       parent_rate = 10 * DUMMY_CLOCK_RATE_1;

Just write out the actual frequency. Don't use DUMMY_CLOCK_RATE_1 at all
in the test.

> +       clk_fractional_divider_general_approximation(hw, rate, &parent_rate, &m, &n);
> +       KUNIT_EXPECT_EQ(test, m, 1);
> +       KUNIT_EXPECT_EQ(test, n, 7);

This is a different test case.

> +
> +       // Highest numerator, no flags
> +       parent_rate = DUMMY_CLOCK_RATE_1 / 10;
> +       clk_fractional_divider_general_approximation(hw, rate, &parent_rate, &m, &n);
> +       KUNIT_EXPECT_EQ(test, m, 7);

Is 7 related to mwidth? Maybe this should be clk_div_mask(fd->mwidth)
instead of 7.

> +       KUNIT_EXPECT_EQ(test, n, 1);

This is a different test case.

> +
> +       // Highest denominator, zero based
> +       parent_rate = 10 * DUMMY_CLOCK_RATE_1;
> +       fd->flags = CLK_FRAC_DIVIDER_ZERO_BASED;
> +       clk_fractional_divider_general_approximation(hw, rate, &parent_rate, &m, &n);
> +       KUNIT_EXPECT_EQ(test, m, 1);
> +       KUNIT_EXPECT_EQ(test, n, 8);

This is a different test case.

> +
> +       // Highest numerator, zero based
> +       parent_rate = DUMMY_CLOCK_RATE_1 / 10;
> +       clk_fractional_divider_general_approximation(hw, rate, &parent_rate, &m, &n);
> +       KUNIT_EXPECT_EQ(test, m, 8);
> +       KUNIT_EXPECT_EQ(test, n, 1);

This is a different test case. If it has a meaningful name it will be
easier to understand as well.