Re: [PATCH v2 5/5] firmware: QCOM_SCM: Allow qcom_scm driver to be loadable as a permenent module

[John Stultz <john.stultz@xxxxxxxxxx>]

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.

thanks
-john