Re: [PATCH 0/8] clk: Add kunit tests for fixed rate and parent data

[Geert Uytterhoeven <geert@linux-m68k.org>]

Hi Frank,

On Sun, Mar 5, 2023 at 4:33 AM Frank Rowand <frowand.list@gmail.com> wrote:
> On 3/2/23 13:47, Geert Uytterhoeven wrote:
> > On Thu, Mar 2, 2023 at 8:28 PM Stephen Boyd <sboyd@kernel.org> wrote:
> >> Quoting Rob Herring (2023-03-02 09:32:09)
> >>> On Thu, Mar 2, 2023 at 2:14 AM David Gow <davidgow@google.com> wrote:
> >>>> On Thu, 2 Mar 2023 at 09:38, Stephen Boyd <sboyd@kernel.org> wrote:
> >>>>> This patch series adds unit tests for the clk fixed rate basic type and
> >>>>> the clk registration functions that use struct clk_parent_data. To get
> >>>>> there, we add support for loading a DTB into the UML kernel that's
> >>>>> running the unit tests along with probing platform drivers to bind to
> >>>>> device nodes specified in DT.
> >>>>>
> >>>>> With this series, we're able to exercise some of the code in the common
> >>>>> clk framework that uses devicetree lookups to find parents and the fixed
> >>>>> rate clk code that scans devicetree directly and creates clks. Please
> >>>>> review.
> >>>>>
> >>>>
> >>>> Thanks Stephen -- this is really neat!
> >>>>
> >>>> This works well here, and I love all of the tests for the
> >>>> KUnit/device-tree integration as well.
> >>>>
> >>>> I'm still looking through the details of it (alas, I've mostly lived
> >>>> in x86-land, so my device-tree knowledge is, uh, spotty to say the
> >>>> least), but apart from possibly renaming some things or similarly
> >>>> minor tweaks, I've not got any real suggestions thus far.
> >>>>
> >>>> I do wonder whether we'll want, on the KUnit side, to have some way of
> >>>> supporting KUnit device trees on non-UML architecctures (e.g., if we
> >>>> need to test something architecture-specific, or on a big-endian
> >>>> platform, etc), but I think that's a question for the future, rather
> >>>> than something that affects this series.
> >>>
> >>> I'll say that's a requirement. We should be able to structure the
> >>> tests to not interfere with the running system's DT. The DT unittest
> >>> does that.
> >>
> >> That could be another choice in the unit test choice menu.
> >> CONFIG_OF_KUNIT_NOT_UML that injects some built-in DTB overlay on an
> >> architecture that wants to run tests.
> >
> > As long as you use compatible values that don't exist elsewhere,
> > and don't overwrite anything, you can load your kunit test overlays
> > on any running system that has DT support.
> >
> >>> As a side topic, Is anyone looking at getting UML to work on arm64?
> >>> It's surprising how much x86 stuff there is which is I guess one
> >>> reason it hasn't happened.
> >>
> >> I've no idea but it would be nice indeed.
> >
> > I believe that's non-trivial. At least for arm32 (I didn't have any arm64
> > systems last time I asked the experts).
> >
> >>>> Similarly, I wonder if there's something we could do with device tree
> >>>> overlays, in order to make it possible for tests to swap nodes in and
> >>>> out for testing.
> >>>
> >>> Yes, that's how the DT unittest works. But it is pretty much one big
> >>> overlay (ignoring the overlay tests). It could probably be more
> >>> modular where it is apply overlay, test, remove overlay, repeat.
> >>
> >> I didn't want to rely on the overlay code to inject DT nodes. Having
> >> tests written for the fake KUnit machine is simple. It closely matches
> >> how clk code probes the DTB and how nodes are created and populated on
> >> the platform bus as devices. CLK_OF_DECLARE() would need the overlay to
> >> be applied early too, which doesn't happen otherwise as far as I know.
> >
> > Don't all generic clock drivers also create a platform driver?
> > At least drivers/clk/clk-fixed-factor.c does.
> >
> >> But perhaps this design is too much of an end-to-end test and not a unit
> >> test? In the spirit of unit testing we shouldn't care about how the node
> >> is added to the live devicetree, just that there is a devicetree at all.
> >>
> >> Supporting overlays to more easily test combinations sounds like a good
> >> idea. Probably some kunit_*() prefixed functions could be used to
> >> apply a test managed overlay and automatically remove it when the test
> >> is over would work. The clk registration tests could use this API to
> >> inject an overlay and then manually call the of_platform_populate()
> >> function to create the platform device(s). The overlay could be built in
> >> drivers/clk/ too and then probably some macroish function can find the
> >> blob and apply it.
> >
> > No need to manually call of_platform_populate() to create the
> > platform devices. That is taken care of automatically when applying
> > an overlay.
> >
> >> Is there some way to delete the platform devices that we populate from
> >> the overlay? I'd like the tests to be hermetic.
>
> > Removing the overlay will delete the platform devices.
>
> I _think_ that is incorrect.  Do you have a pointer to the overlay code that
> deletes the device?  (If I remember correctly, the overlay remove code does not
> even check whether the device exists and whether a driver is bound to it -- but
> this is on my todo list to look into.)

https://elixir.bootlin.com/linux/latest/source/drivers/of/platform.c#L769

> > All of that works if you have your own code to apply a DT overlay.
> > The recent fw_devlinks patches did cause some regressions, cfr.
> > https://lore.kernel.org/all/CAMuHMdXEnSD4rRJ-o90x4OprUacN_rJgyo8x6=9F9rZ+-KzjOg@mail.gmail.com

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

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