On 03-07-20, 13:23, Will Deacon wrote:
> On Tue, Jun 16, 2020 at 01:52:32PM -0700, John Stultz wrote:
> > On Tue, Jun 16, 2020 at 12:55 AM Marc Zyngier <m...@kernel.org> wrote:
> > > On 2020-06-16 07:13, John Stultz wrote:
> > > > diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
> > > > index b510f67dfa49..714893535dd2 100644
> > > > --- a/drivers/iommu/Kconfig
> > > > +++ b/drivers/iommu/Kconfig
> > > > @@ -381,6 +381,7 @@ config SPAPR_TCE_IOMMU
> > > > config ARM_SMMU
> > > > tristate "ARM Ltd. System MMU (SMMU) Support"
> > > > depends on (ARM64 || ARM || (COMPILE_TEST && !GENERIC_ATOMIC64))
> > > > &&
> > > > MMU
> > > > + depends on QCOM_SCM || !QCOM_SCM #if QCOM_SCM=m this can't be =y
> > >
> > > This looks a bit ugly. Could you explain why we need this at the SMMU
> > > level? I'd have expected the dependency to flow the other way around...
> >
> > Yea, so the arm-smmu-qcom.c file calls directly into the qcom-scm code
> > via qcom_scm_qsmmu500_wait_safe_toggle()
> >
> > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/iommu/arm-smmu-qcom.c?h=v5.8-rc1#n44
> >
> > So if ARM_SMMU=y and QCOM_SCM=m we get:
> > drivers/iommu/arm-smmu-qcom.o: In function `qcom_smmu500_reset':
> > arm-smmu-qcom.c:(.text+0xb4): undefined reference to
> > `qcom_scm_qsmmu500_wait_safe_toggle'
> >
> > Do you have a suggestion for an alternative approach?
>
> Can you use symbol_get() or something like that? How are module dependencies
> handled by other drivers?
So drivers deal with this by making rules in Kconfig which will prohibit
this case. QCOM_SCM depends on ARM_SMMU with the caveat that if ARM_SMMU
is a module, QCOM_SCM cant be inbuilt.
This can be done by adding below line in Kconfig for QCOM_SCM:
depends on ARM_SMMU || !ARM_SMMU
This is quite prevalent is drivers to ensure dependency like this
Thanks
--
~Vinod
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