Re: [PATCH 0/2] clk: kunit: Fix the lockdep warnings

[Maxime Ripard]

Hi Stephen,

On Wed, Aug 09, 2023 at 06:37:30PM -0700, Stephen Boyd wrote:
> Quoting Stephen Boyd (2023-08-09 16:21:50)
> > +kunit-dev
> > 
> > Quoting Maxime Ripard (2023-07-21 00:09:31)
> > > Hi,
> > > 
> > > Here's a small series to address the lockdep warning we have when
> > > running the clk kunit tests with lockdep enabled.
> > > 
> > > For the record, it can be tested with:
> > > 
> > > $ ./tools/testing/kunit/kunit.py run \
> > >     --kunitconfig=drivers/clk \
> > >     --cross_compile aarch64-linux-gnu- --arch arm64 \
> > >     --kconfig_add CONFIG_DEBUG_KERNEL=y \
> > >     --kconfig_add CONFIG_PROVE_LOCKING=y
> > > 
> > > Let me know what you think,
> > 
> > Thanks for doing this. I want to roll these helpers into the clk_kunit.c
> > file that I had created for some other clk tests[1]. That's mostly
> > because clk.c is already super long and adding kunit code there makes
> > that problem worse. I'll try to take that patch out of the rest of the
> > series and then add this series on top and resend.
> > 
> > I don't know what to do about the case where CONFIG_KUNIT=m though. We
> > have to export clk_prepare_lock/unlock()? I really don't want to do that
> > even if kunit is enabled (see EXPORT_SYMBOL_IF_KUNIT). Maybe if there
> > was a GPL version of that, so proprietary modules can't get at kernel
> > internals on kunit enabled kernels.
> > 
> > But I also like the approach taken here of adding a small stub around
> > the call to make sure a test is running. Maybe I'll make a kunit
> > namespaced exported gpl symbol that bails if a test isn't running and
> > calls the clk_prepare_lock/unlock functions inside clk.c and then move
> > the rest of the code to clk_kunit.c to get something more strict.
> > 
> 
> What if we don't try to do any wrapper or export symbols and test
> __clk_determine_rate() how it is called from the clk framework? The
> downside is the code is not as simple because we have to check things
> from within the clk_ops::determine_rate(), but the upside is that we can
> avoid exporting internal clk APIs or wrap them so certain preconditions
> are met like requiring them to be called from within a clk_op.

The main reason for that test was linked to commit 262ca38f4b6e ("clk:
Stop forwarding clk_rate_requests to the parent"). Prior to it, if a
clock had CLK_SET_RATE_PARENT, we could end up with its parent's parent
hw struct and rate in best_parent_*.

So that test was mostly about making sure that __clk_determine_rate will
properly set the best_parent fields to match the clock's parent.

If we do a proper clock that uses __clk_determine_rate, we lose the
ability to check the content of the clk_rate_request returned by
__clk_determine_rate. It's up to you to tell whether it's a bad thing or
not :)

> I also find it very odd to call clk_mux_determine_rate_closest() from a
> clk that has one parent.

Yeah, the behaviour difference between determine_rate and
determine_rate_closest is weird to me too. We discussed it recently here:
https://lore.kernel.org/linux-clk/mlgxmfim3poke2j45vwh2htkn66hrrjd6ozjebtqhbf4wwljwo@hzi4dyplhdqg/

> Maybe the clk op should call clk_hw_forward_rate_request() followed by
> __clk_determine_rate() on the parent so we can test what the test
> comment says it wants to test.

I guess that would work too :)

Maxime

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