Re: [PATCH 2/8] of: Enable DTB loading on UML for KUnit tests

[Stephen Boyd <sboyd@kernel.org>]

Quoting David Gow (2023-03-02 23:15:04)
> On Thu, 2 Mar 2023 at 09:38, Stephen Boyd <sboyd@kernel.org> wrote:
> >
> > To fully exercise common clk framework code in KUnit we need to
> > associate 'struct device' pointers with 'struct device_node' pointers so
> > that things like clk_get() can parse DT nodes for 'clocks' and so that
> > clk providers can use DT to provide clks; the most common mode of
> > operation for clk providers.
> >
> > Adding support to KUnit so that it loads a DTB is fairly simple after
> > commit b31297f04e86 ("um: Add devicetree support"). We can simply pass a
> > pre-compiled deviectree blob (DTB) on the kunit.py commandline and UML
> > will load it. The problem is that tests won't know that the commandline
> > has been modified, nor that a DTB has been loaded. Take a different
> > approach so that tests can skip if a DTB hasn't been loaded.
> >
> > Reuse the Makefile logic from the OF unittests to build a DTB into the
> > kernel. This DTB will be for the mythical machine "linux,kunit", i.e.
> > the devicetree for the KUnit "board". In practice, it is a dtsi file
> > that will gather includes for kunit tests that rely in part on a
> > devicetree being loaded. The devicetree should only be loaded if
> > CONFIG_OF_KUNIT=y. Make that a choice config parallel to the existing
> > CONFIG_OF_UNITTEST so that only one devicetree can be loaded in the
> > system at a time. Similarly, the kernel commandline option to load a
> > DTB is ignored if CONFIG_OF_KUNIT is enabled so that only one DTB is
> > loaded at a time.
> 
> This feels a little bit like it's just papering over the real problem,
> which is that there's no way tests can skip themselves if no DTB is
> loaded.

Hmm. I think you're suggesting that the unit test data be loaded
whenever CONFIG_OF=y and CONFIG_KUNIT=y. Then tests can check for
CONFIG_OF and skip if it isn't enabled?

> 
> That being said, I do think that there's probably some sense in
> supporting the compiled-in DTB as well (it's definitely simpler than
> patching kunit.py to always pass the extra command-line option in, for
> example).
> But maybe it'd be nice to have the command-line option override the
> built-in one if present.

Got it. I need to test loading another DTB on the commandline still, but
I think this won't be a problem. We'll load the unittest-data DTB even
with KUnit on UML, so assuming that works on UML right now it should be
unchanged by this series once I resend.