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

[Frank Rowand <frowand.list@gmail.com>]

On 3/5/23 03:26, Geert Uytterhoeven wrote:
> 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

Thanks!  That is precisely what I failed to remember.

-Frank

> 
>>> 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
> 


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