Re: [PATCH 1/2] clk: Drive clk_leaf_mux_set_rate_parent test from clk_ops

Stephen Boyd
2023-10-10T03:23:11Z

Quoting Stephen Boyd (2023-09-12 10:55:30)
> Running this kunit test with lockdep enabled leads to warning splats
> about calling clk provider APIs without the clk_prepare lock held. I
> proposed adding a wrapper around these APIs to grab the prepare lock so
> we can call them from anywhere, and Maxime implemented that approach[1],
> but it didn't look great. That's because we had to make more kunit
> testing APIs just to call code from a place that isn't a clk provider
> when the prepare lock isn't held.
>
> Instead of doing that, let's implement a determine_rate clk_op for a new
> leaf clk that is the child of the existing leaf clk. We can call
> __clk_determine_rate() on the existing leaf clk from there, and stash
> away the clk_rate_request struct to check once the clk_op returns. Drive
> that clk_op by calling clk_round_rate() to keep things similar to how it
> was before (i.e. nothing actually changes rate, just the new rate is
> determined). This silences the warning by driving the test from a
> clk_op where we know the prepare lock is held.
>
> While looking at this in more detail, it was determined that the code we
> intended to test in commit 262ca38f4b6e ("clk: Stop forwarding
> clk_rate_requests to the parent") wasn't actually tested. The call to
> __clk_determine_rate() wasn't actually getting to the newly introduced
> code under the CLK_SET_RATE_PARENT if condition in
> clk_core_round_rate_nolock() because the parent clk (the mux) could
> round rates. We introduce a new leaf and make sure the parent of that
> clk has no clk_ops so that we can be certain that the
> CLK_SET_RATE_PARENT condition in clk_core_round_rate_nolock() is
> evaluated.
>
> Reported-by: Guenter Roeck <linux@roeck-us.net>
> Closes: https://lore.kernel.org/linux-clk/2b594e50-2bbf-4a2d-88e6-49fc39f3957a@roeck-us.net/
> Reported-by: kernel test robot <yujie.liu@intel.com>
> Closes: https://lore.kernel.org/oe-lkp/202301310919.b9d56ee3-yujie.liu@intel.com
> Cc: Maxime Ripard <mripard@kernel.org>
> Link: https://lore.kernel.org/r/20230721-clk-fix-kunit-lockdep-v1-0-32cdba4c8fc1@kernel.org [1]
> Fixes: 262ca38f4b6e ("clk: Stop forwarding clk_rate_requests to the parent")
> Signed-off-by: Stephen Boyd <sboyd@kernel.org>
> ---

Applied to clk-next