Re: [PATCH v6 7/7] clk: test: introduce additional test case showing v2 rate change + LCM parent

[Brian Masney]

On Thu, Mar 19, 2026 at 5:43 AM Maxime Ripard <mripard@xxxxxxxxxx> wrote:
> On Fri, Mar 13, 2026 at 12:43:14PM -0400, Brian Masney wrote:
> > Add a test case that uses the clk divider with the v2 rate negotiation
> > logic, plus the Lowest Common Multiple (LCM) to calculate the optimal
> > parent rate. The test ensures that the parent clk rate is set to a rate
> > that's acceptable to both children, and the sibling clock is not
> > affected.
> >
> > The test in this commit use the following simplified clk tree with
> > the initial state:
> >
> >                      parent
> >                      24 MHz
> >                     /      \
> >               child1        child2
> >               24 MHz        24 MHz
> >
> > child1 and child2 both divider-only clocks that have CLK_SET_RATE_PARENT
> > set, and the parent is capable of achieving any rate.
> >
> > child1 requests 32 MHz, and the tree ends up with the correct state:
> >
> >                      parent
> >                      96 MHz
> >                     /      \
> >               child1        child2
> >               32 MHz        24 MHz
> >               div=3          div=4
> >
> > Additionally, add a note about why clk_dummy_div_lcm_ops + friends are
> > still needed.
> >
> > Link: https://lore.kernel.org/linux-clk/aUSWU7UymULCXOeF@xxxxxxxxxx/
> > Link: https://lpc.events/event/19/contributions/2152/
> > Signed-off-by: Brian Masney <bmasney@xxxxxxxxxx>
> > ---
> >  drivers/clk/clk_test.c | 49 +++++++++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 49 insertions(+)
> >
> > diff --git a/drivers/clk/clk_test.c b/drivers/clk/clk_test.c
> > index 40bc01a0259d8d49ca4c1983b6c10a3684a95f0b..00511afe5faa8b2631633ab796ece1bfe6944fb5 100644
> > --- a/drivers/clk/clk_test.c
> > +++ b/drivers/clk/clk_test.c
> > @@ -181,6 +181,14 @@ static const struct clk_ops clk_dummy_div_ops = {
> >       .set_rate = clk_dummy_div_set_rate,
> >  };
> >
> > +/*
> > + * drivers/clk/clk-divider.c has support for v2 rate negotiation, and setting
> > + * the parent based on the LCM, however we need to be able to test just setting
> > + * the parent rate based on the LCM, and not set the v2 rate negotiation flag.
> > + * This is to demonstrate existing functionality in the clk core, and ensure it
> > + * stays the same. That's why we need to keep clk_dummy_div_lcm_ops, and can't
> > + * just use clk_dummy_div_ops.
> > + */
> >  static int clk_dummy_div_lcm_determine_rate(struct clk_hw *hw,
> >                                           struct clk_rate_request *req)
> >  {
> > @@ -709,6 +717,18 @@ clk_rate_change_sibling_div_div_test_lcm_ops_v1_params[] = {
> >  KUNIT_ARRAY_PARAM_DESC(clk_rate_change_sibling_div_div_test_lcm_ops_v1,
> >                      clk_rate_change_sibling_div_div_test_lcm_ops_v1_params, desc)
> >
> > +static const struct clk_rate_change_sibling_div_div_test_param
> > +clk_rate_change_sibling_div_div_test_regular_ops_v2_params[] = {
> > +     {
> > +             .desc = "regular_ops_v2",
> > +             .ops = &clk_dummy_div_ops,
> > +             .extra_child_flags = CLK_V2_RATE_NEGOTIATION,
> > +     },
> > +};
> > +
> > +KUNIT_ARRAY_PARAM_DESC(clk_rate_change_sibling_div_div_test_regular_ops_v2,
> > +                    clk_rate_change_sibling_div_div_test_regular_ops_v2_params, desc)
> > +
> >  static int clk_rate_change_sibling_div_div_test_init(struct kunit *test)
> >  {
> >       const struct clk_rate_change_sibling_div_div_test_param *param = test->param_value;
> > @@ -836,6 +856,31 @@ static void clk_test_rate_change_sibling_div_div_3_v1(struct kunit *test)
> >       KUNIT_EXPECT_EQ(test, ctx->child2.div, 1);
> >  }
> >
> > +/*
> > + * Test that, for a parent with two divider-only children with CLK_SET_RATE_PARENT
> > + * set and one requests a rate incompatible with the existing parent rate, the
> > + * sibling rate is not affected, and maintains it's rate.
> > + */
>
> I assume that's only true if the v2 negociation is enabled?

Correct.

> > +static void clk_test_rate_change_sibling_div_div_4_v2(struct kunit *test)
> > +{
> > +     struct clk_rate_change_sibling_div_div_context *ctx = test->priv;
> > +     int ret;
> > +
> > +     ret = clk_set_rate(ctx->child1_clk, 32 * HZ_PER_MHZ);
> > +     KUNIT_ASSERT_EQ(test, ret, 0);
>
> If so, we should have an assertion here

OK, I'll add that in the next version, and update the description.
I'll also add a similar assertion to the other tests.

Brian