linux-kernel - Re: [PATCH] clk: explicitly disable CONFIG_UML_PCI_OVER

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Date:   Mon, 11 Jul 2022 16:03:08 -0700
From:   Daniel Latypov <dlatypov@...gle.com>
To:     Stephen Boyd <sboyd@...nel.org>
Cc:     brendanhiggins@...gle.com, davidgow@...gle.com,
        linux-kernel@...r.kernel.org, kunit-dev@...glegroups.com,
        linux-kselftest@...r.kernel.org, skhan@...uxfoundation.org,
        linux-clk@...r.kernel.org, Maxime Ripard <maxime@...no.tech>
Subject: Re: [PATCH] clk: explicitly disable CONFIG_UML_PCI_OVER_VIRTIO in .kunitconfig

On Mon, Jul 11, 2022 at 1:49 PM Stephen Boyd <sboyd@...nel.org> wrote:
>
> Quoting Daniel Latypov (2022-07-11 09:27:13)
> > CONFIG_UML_PCI_OVER_VIRTIO=y is needed to enable CONFIG_PCI=y on UML.
> > However, this causes test failures when running the clk tests, i.e.
> > $ ./tools/testing/kunit/kunit.py run --kunitconfig=drivers/clk
> >
> > A snippet of the particular error is:
> > >     ok 1 - clk_gate_test_parent_rate
> > > ------------[ cut here ]------------
> > > WARNING: CPU: 0 PID: 45 at lib/logic_iomem.c:141 __raw_readl+0x9f/0xd0
> >
> > This is triggered by this cast in the test:
> >    143          ctx->fake_mem = (void __force __iomem *)&ctx->fake_reg;
> > this seems to work except when logic iomem is enabled, i.e.
> > CONFIG_INDIRECT_IOMEM=y.
> >
> > As a short-term fix, explicitly disable CONFIG_UML_PCI_OVER_VIRTIO in
> > drivers/clk/.kunitconfig so we can enable it for everyone else by
> > default in kunit.py.
> >
> > The long-term fix probably requires something more complicated, like
> >   #ifdef CONFIG_INDIRECT_IOMEM
> >     logic_iomem_add_region(...);
> >   #endif
>
> If this is how platform IO is mocked then yes we'll have to implement
> that.

It's not clear that it will be, but it's likely.
Until it's more clear, I figured we'd go with this simple bandaid fix for now.

There was initially some talk of using function-level
"stubbing"/"mocking" [1] to do the same, but Brendan started playing
around with logic iomem more. He and David can comment on it more
cogently than I can.

[1] https://lore.kernel.org/linux-kselftest/20220318021314.3225240-3-davidgow@google.com/

Daniel