[PATCH] iommu: fix ARM_SMMU vs QCOM_SCM compilation

[Dmitry Baryshkov]

On Mon, 11 Oct 2021 at 09:09, Arnd Bergmann <arnd at arndb.de> wrote:
>
> On Mon, Oct 11, 2021 at 6:11 AM Dmitry Baryshkov
> <dmitry.baryshkov at linaro.org> wrote:
> > On Sun, 10 Oct 2021 at 20:42, Arnd Bergmann <arnd at arndb.de> wrote:
> >
> > The patch seems correct, but it becomes overcomplicated. What about:
> > - restoring QCOM_SCM stubs
>
> The stubs are what has led to the previous bugs in this area to often
> go unnoticed for too long, as illustrated by your suggestion
>
> > - making ARM_SMMU select QCOM_SCM if ARM_SMMU_QCOM
>
> I assume you meant "select QCOM_SCM if ARCH_QCOM",
> after we stop using ARM_SMMU_QCOM?
>
> > This would have almost the same result as with your patch, but without
> > extra ARM_SMMU_QCOM Kconfig symbol.
>
> The "almost" is the problem: consider the case of
>
> CONFIG_ARM=y
> CONFIG_COMPILE_TEST=y
> CONFIG_ARCH_QCOM=n
> CONFIG_ARM_SMMU=y
> CONFIG_DRM_MSM=m
> CONFIG_QCOM_SCM=m (selected by DRM_MSM)
>
> The stubs here lead to ARM_SMMU linking against the QCOM_SCM
> driver from built-in code, which fails because QCOM_SCM itself
> is a loadable module.

I see. The idealist in me wishes to change my suggestion to
'select QCOM_SCM if ARCH_QCOM || COMPILE_TEST'
but I have the subtle feeling that this also might fail somehow.

>
> We can move the "select QCOM_SCM" in the ARM_SMMU_QCOM
> symbol if we make that a tristate though, if you want to separate it
> a little more.

This would complicate things a bit, as we would no longer be able to
use 'arm-smmu-$(CONFIG_ARM_SMMU_QCOM) +=' construct.

-- 
With best wishes
Dmitry