KUnit issues - Was: [igt-dev] [PATCH RFC v2 8/8] drm/i915: check if current->mm is not NULL

[Daniel Latypov]

On Mon, Nov 7, 2022 at 10:38 AM Michał Winiarski
<michal.winiarski at intel.com> wrote:
>
> On Thu, Nov 03, 2022 at 04:23:02PM +0100, Mauro Carvalho Chehab wrote:
> > Hi,
> >
> > I'm facing a couple of issues when testing KUnit with the i915 driver.
> >
> > The DRM subsystem and the i915 driver has, for a long time, his own
> > way to do unit tests, which seems to be added before KUnit.
> >
> > I'm now checking if it is worth start using KUnit at i915. So, I wrote
> > a RFC with some patches adding support for the tests we have to be
> > reported using Kernel TAP and KUnit.
> >
> > There are basically 3 groups of tests there:
> >
> > - mock tests - check i915 hardware-independent logic;
> > - live tests - run some hardware-specific tests;
> > - perf tests - check perf support - also hardware-dependent.
> >
> > As they depend on i915 driver, they run only on x86, with PCI
> > stack enabled, but the mock tests run nicely via qemu.
> >
> > The live and perf tests require a real hardware. As we run them
> > together with our CI, which, among other things, test module
> > unload/reload and test loading i915 driver with different
> > modprobe parameters, the KUnit tests should be able to run as
> > a module.
>
> Note that KUnit tests that are doing more of a functional/integration
> testing (on "live" hardware) rather than unit testing (where hardware
> interactions are mocked) are not very common.
> Do we have other KUnit tests like this merged?

I don't think we have other tests like this.

> Some of the "live tests" are not even that, being more of a pure
> hardware tests (e.g. live_workarounds, which is checking whether values
> in MMIO regs stick over various HW state transitions).
>
> I'm wondering, is KUnit the right tool for this job?

The main focus of KUnit is for hw-independent tests.
So in theory: no.

But I can imagine it could be easier to write the validation via
KUNIT_EXPECT_EQ and friends as opposed to writing your own kernel
module w/ its own set of macros, etc.

So my first thought is: "if it works, then you can try using it."
(Might want to take steps like make sure they don't get enabled by
CONFIG_KUNIT_ALL_TESTS=y).

Talking with David, he seems to have echoed my thoughts.
David also suggested that maybe the test could use a fake of the hw by
default, but have an option to run against real hw when available.
I think that sounds like a good chunk of work, so I don't know if you
need to worry about that.

Daniel