On Fri, Jul 10, 2020 at 12:54 AM Will Deacon <will@xxxxxxxxxx> wrote: > On Thu, Jul 09, 2020 at 08:28:45PM -0700, John Stultz wrote: > > On Thu, Jul 2, 2020 at 7:18 AM Will Deacon <will@xxxxxxxxxx> wrote: > > > On Thu, Jun 25, 2020 at 12:10:39AM +0000, 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 > > > > select IOMMU_API > > > > select IOMMU_IO_PGTABLE_LPAE > > > > select ARM_DMA_USE_IOMMU if ARM > > > > > > This looks like a giant hack. Is there another way to handle this? > > > > Sorry for the slow response here. > > > > So, I agree the syntax looks strange (requiring a comment obviously > > isn't a good sign), but it's a fairly common way to ensure drivers > > don't get built in if they optionally depend on another driver that > > can be built as a module. > > See "RFKILL || !RFKILL", "EXTCON || !EXTCON", or "USB_GADGET || > > !USB_GADGET" in various Kconfig files. > > > > I'm open to using a different method, and in a different thread you > > suggested using something like symbol_get(). I need to look into it > > more, but that approach looks even more messy and prone to runtime > > failures. Blocking the unwanted case at build time seems a bit cleaner > > to me, even if the syntax is odd. > > Maybe just split it out then, so that the ARM_SMMU entry doesn't have this, > as that driver _really_ doesn't care about SoC details like this. In other > words, add a new entry along the lines of: > > config ARM_SMMU_QCOM_IMPL > default y > #if QCOM_SCM=m this can't be =y > depends on ARM_SMMU & (QCOM_SCM || !QCOM_SCM) > > and then have arm-smmu.h provide a static inline qcom_smmu_impl_init() > which returns -ENODEV if CONFIG_ARM_SMMU_QCOM_IMPL=n and hack the Makefile > so that we don't bother to compile arm-smmu-qcom.o in that case. > > Would that work? I think this proposal still has problems with the directionality of the call. The arm-smmu-impl.o calls to arm-smmu-qcom.o which calls qcom_scm.o So if qcom_scm.o is part of a module, the calling code in arm-smmu-qcom.o also needs to be a module, which means CONFIG_ARM_SMMU needs to be a module. I know you said the arm-smmu driver doesn't care about SoC details, but the trouble is that currently the arm-smmu driver does directly call the qcom-scm code. So it is a real dependency. However, if QCOM_SCM is not configured, it calls stubs and that's ok. In that way, the "depends on QCOM_SCM || !QCOM_SCM" line actually makes sense. It looks terrible because we're used to boolean logic, but it's ternary. Maybe can have the ARM_SMMU_QCOM_IMPL approach you suggest above, but that just holds the issue out at arms length, because we're still going to need to have: depends on ARM_SMMU_QCOM_IMPL || !ARM_SMMU_QCOM_IMPL in the ARM_SMMU definition, which I suspect you're wanting to avoid. Otherwise the only thing I can think of is a deeper reworking of the arm-smmu-impl code so that the arm-smmu-qcom code probes itself and registers its hooks with the arm-smmu core. That way the arm-smmu driver would not directly call any SoC specific code (and thus have no dependencies outward). But it's probably a fair amount of churn vs the extra depends string. thanks -john
