linux-kernel - Re: [RFC][PATCH 5/5] firmware: QCOM_SCM: Allow qcom_scm driver to be loadable as a permenent module

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Date:   Tue, 16 Jun 2020 13:52:32 -0700
From:   John Stultz <john.stultz@...aro.org>
To:     Marc Zyngier <maz@...nel.org>
Cc:     lkml <linux-kernel@...r.kernel.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Linus Walleij <linus.walleij@...aro.org>,
        Lina Iyer <ilina@...eaurora.org>,
        Saravana Kannan <saravanak@...gle.com>,
        Todd Kjos <tkjos@...gle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        iommu@...ts.linux-foundation.org, linux-gpio@...r.kernel.org,
        Will Deacon <will@...nel.org>
Subject: Re: [RFC][PATCH 5/5] firmware: QCOM_SCM: Allow qcom_scm driver to be
 loadable as a permenent module

On Tue, Jun 16, 2020 at 12:55 AM Marc Zyngier <maz@...nel.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?

thanks
-john